[globalisel][tablegen] Compute available feature bits correctly.

[dsanders]

Summary

Predicate<> now has a field to indicate how often it must be recomputed.
Currently, there are two frequencies, per-module (RecomputePerFunction==0)
and per-function (RecomputePerFunction==1). Per-function predicates are
currently recomputed more frequently than necessary since the only predicate
in this category is cheap to test. Per-module predicates are now computed in
getSubtargetImpl() while per-function predicates are computed in selectImpl().

Tablegen now manages the PredicateBitset internally. It should only be
necessary to add the required includes.

Also fixed a problem revealed by the test case where
constrainSelectedInstRegOperands() would attempt to tie operands that
BuildMI had already tied.

[rovka]

So, we have a new GISelAccessor with a new InstructionSelector for each unique subtarget (module + function attributes, as hashed in getSubtargetImpl). Why do we need to have module features and function features in each InstructionSelector? Isn't there a different InstructionSelector for each kind of function, and don't we magically get the right one when processing each function? What am I missing? It seems to me that we could get away with a single set of availableFeatures per InstructionSelector.

In any case, I think you need a more complex test with several different functions with different attributes to make sure you're computing the correct features for each function and you don't have any stale info lingering between them (something like what I do with function attributes in arm-instruction-select.mir, although that's just for convenience and not for this exact purpose).

include/llvm/Target/Target.td

538

This looks very easy to forget to set when adding a new predicate. Would it make sense to have 2 subclasses of Predicate (ModulePredicate and FunctionPredicate) and define all the predicates based on them? Naturally, it would be a pretty big mechanical change to update all the targets, so it should be a separate patch, but I think it would make things easier to maintain in the long run. What do you think?

lib/Target/AArch64/AArch64InstructionSelector.cpp

53

This doesn't look like it would scale very well if we needed to add more function-level predicates. Is there any significant disadvantage to threading the MachineFunction all the way down here? Then we'd only have to update the constructor, without createXInstructionSelector etc.

lib/Target/AArch64/AArch64TargetMachine.cpp

266

Nit: I guess it doesn't matter much, since this is only used for hashing, but it would be nice to keep the convention used for the target features etc (",+forcodesize").

[dsanders]

In D32491#737781, @rovka wrote:

So, we have a new GISelAccessor with a new InstructionSelector for each unique subtarget (module + function attributes, as hashed in getSubtargetImpl). Why do we need to have module features and function features in each InstructionSelector? Isn't there a different InstructionSelector for each kind of function, and don't we magically get the right one when processing each function? What am I missing? It seems to me that we could get away with a single set of availableFeatures per InstructionSelector.

getSubtargetImp() only has access to the Function* but NotWin64WithoutFP needs the MachineFunction* to evaluate Subtarget->getFrameLowering()->hasFP(*MF). It's possible to go from MachineFunction* to Function* but not the other way. Also, the value of hasFP() changes from pass to pass as the stack layout becomes more concrete.

In any case, I think you need a more complex test with several different functions with different attributes to make sure you're computing the correct features for each function and you don't have any stale info lingering between them (something like what I do with function attributes in arm-instruction-select.mir, although that's just for convenience and not for this exact purpose).

Ok.

include/llvm/Target/Target.td

538

If your predicate references MF you'll get a compile error since MF isn't declared in computeAvailableModuleFeatures. Things implemented via class members (e.g. ForCodeSize but that one is ok because of the cache) will silently do the wrong thing. Even without that, I think renaming to ModulePredicate/FunctionPredicate would be a good change to make since it's clearer.

If we're going to rename Predicate, we should probably take the opportunity to add ISel/CG/CodeGen or similar to the name too.

One thing that's a bit weird here is that predicates using ForCodeSize and similar would be ModulePredicate's because of the cache in getSubtargetImpl() even though they're logically per-function predicates.

lib/Target/AArch64/AArch64InstructionSelector.cpp

53

The caller doesn't have access to MachineFunction so I assume you meant Function. I'm not sure about threading that down since it moves the predicate testing away from the cache key generator. It would be easy to add a predicate in the instruction selector and forget to update the key generator. I agree we need to do something here though. I'll have a think about it.

lib/Target/AArch64/AArch64TargetMachine.cpp

266

Ok. And presumably we'd have "-forcodesize" instead of "" if we're matching that convention.

[rovka]

Thanks for all the explanations!
LGTM with that extra test, we can keep discussing the remaining points but I think it's ok to iterate in-tree. I'd really, really like to see the default change from 0 to 1 on RecomputePerFunction, it seems safer that way.

include/llvm/Target/Target.td

538

Hmm, actually, in light of your more detailed explanations, I'm not so sure Module vs Function is the right abstraction here. The matter of whether or not a predicate is safe to cache doesn't seem to correlate as well as I was hoping with whether or not it's a function predicate. Maybe we should have something like CacheablePredicate (or StablePredicate? or ConstantPredicate?), and use that everywhere except where it's not safe to cache? That would force people to either decide that something is safe to cache or fall back to the slow-but-correct path of recomputing it every time.

Also, +1 for finding a better name for these predicates in general, I hate having to explain to people that this isn't about flag registers and condition codes every time :)

lib/Target/AArch64/AArch64InstructionSelector.cpp

53

That's a good point.

lib/Target/AArch64/AArch64TargetMachine.cpp

266

Yup.

[dsanders]

I'm having trouble improving the test case since the function-level predicates don't show up in any importable rules yet. I'll see if I can uncover one

include/llvm/Target/Target.td

538

SubtargetPredicate and FunctionPredicate might be a better fit. SubtargetPredicate would cover both module-level predicates and function-level predicates that are part of the subtarget key.

One thing that's a bit weird here is that predicates using ForCodeSize and similar would be
ModulePredicate's because of the cache in getSubtargetImpl() even though they're logically
per-function predicates.

Following on from the same line of thought, I think I've fixed this weirdness. It turns out that all of these can be moved to subtarget accessors without breaking SelectionDAG. This solves the scalability issue you mention on the AArch64InstructionSelector constructor. I've updated this patch with this change.

For naming RecomputePerFunction: How about RequiresMachineFunction? It dodges the issue of caching function-level information in the subtarget and it's a bit more obvious that it's how you get access to MF.

lib/Target/AArch64/AArch64InstructionSelector.cpp

53

I've found it's possible to avoid passing the flags down (see above). I've updated the patch.

[dsanders]

Moved ForCodeSize and similar to the Subtarget.

[rovka]

In D32491#739333, @dsanders wrote:

I'm having trouble improving the test case since the function-level predicates don't show up in any importable rules yet. I'll see if I can uncover one

Ok, if that's impossible to do now, you should commit as-is and open a PR in bugzilla to add a test for this when we import more rules (otherwise we'll almost surely forget).

include/llvm/Target/Target.td

538

RequiresMachineFunction is not bad, but is the way we access the MF really the issue here? I'm not convinced that the distinction between Function and MachineFunction is that important. Suppose we had the same caching system for MachineFunction as we do for Function - those predicates would still need to be recomputed since, as you explained, they could change by the time we reach our pass.

For pretty much the same reason, I don't think SubtargetPredicate is explicit enough. Predicates that change are very rare, so people will be tempted to just use SubtargetPredicate everywhere without giving it a second thought. We need something that will draw attention to the fact that the predicate may be cached, or at least something that sounds strange enough that it would make people check the comments to see what the big deal is.

Anyway, sorry about bikeshedding this so much :)

lib/Target/AArch64/AArch64InstructionSelector.cpp

53

Cool.

[dsanders]

Add support for patterns consisting solely of an IntInit* and use this to add a
test case to the rule predicate support... almost.

The new test case is currently XFAIL'ed since X86's GlobalISel gives precedence
to the C++ over the tablegenerated code. If you comment out the 'if (selectConstant(...))'
from X86InstructionSelect::select(), it passes the optsize functions but fails the
non-optsize functions (because the support is commented out). Conversely,
leaving it in causes the opposite behaviour. The optsize functions pick the
wrong insn (because C++ beats tablegen) but the non-optsize functions pass.

@rovka: If this updated patch looks good to you then I can commit it and file a
PR about the XFAIL. Otherwise I can commit the previous version and file a PR
about the missing test. Which do you think is best?

[dsanders]

include/llvm/Target/Target.td

538

RequiresMachineFunction is not bad, but is the way we access the MF really
the issue here? I'm not convinced that the distinction between Function and
MachineFunction is that important. Suppose we had the same caching system
for MachineFunction as we do for Function - those predicates would still need
to be recomputed since, as you explained, they could change by the time we
reach our pass.

I was thinking it could be about whether MF is declared or not but this doesn't make sense now that I've realized my mistake below.

For pretty much the same reason, I don't think SubtargetPredicate is explicit
enough. Predicates that change are very rare, so people will be tempted to
just use SubtargetPredicate everywhere without giving it a second thought.
We need something that will draw attention to the fact that the predicate may
be cached, or at least something that sounds strange enough that it would
make people check the comments to see what the big deal is.

I see your point. For some reason I was thinking "as long as a predicate is accessing values from the Subtarget it's not important whether it's a cached value from the function" but that's obviously not true if we don't call computeAvailableModuleFeatures() again after swapping out a Subtarget.

Anyway, sorry about bikeshedding this so much :)

No worries. If we don't pick a good enough name then we'll be doomed to explain it every time it confuses someone so I'd prefer to get it right.

[rovka]

I think this patch is already doing a lot of things, I'd prefer committing the support for immediates separately and opening a PR for the test (and you can attach the X86 test to it so we can discuss with Igor). I need to double check this, but I think if I enable this for ARM (which I intend to do after this goes in) the existing ARM tests will already exercise this (for G_SDIV).

[dsanders]

In that case I'll commit the previous version of this patch tomorrow and post the immediate support for a separate review. The PR can then come out of that review. Thanks

[rovka]

I just checked and the existing ARM tests fail without this patch because the available features aren't reset when entering the functions. They work with this patch + enabling the TableGen selector for ARM, so we'll have tests then :)

[dsanders]

In D32491#740829, @rovka wrote:

I just checked and the existing ARM tests fail without this patch because the available features aren't reset when entering the functions. They work with this patch + enabling the TableGen selector for ARM, so we'll have tests then :)

Thanks.

Before this patch the available features weren't computed at all (the code was never called) so just to double check. Are you checking tests that only need module-level predicates or do they include predicates that vary between functions? The former is covered by select-inc.mir, but the latter doesn't have a working test yet.

include/llvm/CodeGen/GlobalISel/InstructionSelector.h

public:
   }
 };
 
 /// Provides the logic to select generic machine instructions.
 class InstructionSelector {
 public:
   virtual ~InstructionSelector() {}
 
-  /// This is executed before selecting a function.
-  virtual void beginFunction(const MachineFunction &MF) {}
-
   /// Select the (possibly generic) instruction \p I to only use target-specific
   /// opcodes. It is OK to insert multiple instructions, but they cannot be
   /// generic pre-isel instructions.
   ///
   /// \returns whether selection succeeded.
   /// \pre  I.getParent() && I.getParent()->getParent()
   /// \post
   ///   if returns true:

include/llvm/Target/Target.td

class Predicate<string cond> {
   /// It can also list multiple features separated by ",".
   /// e.g. "ModeThumb,FeatureThumb2" is translated to
   ///      "(Bits & ModeThumb) != 0 && (Bits & FeatureThumb2) != 0".
   string AssemblerCondString = "";
 
   /// PredicateName - User-level name to use for the predicate. Mainly for use
   /// in diagnostics such as missing feature errors in the asm matcher.
   string PredicateName = "";
+
+  /// Setting this to '1' indicates that the predicate must be recomputed on
+  /// every function change. Most predicates can leave this at '0'.
+  ///
+  /// Ignored by SelectionDAG, it always recomputes the predicate on every use.
+  bit RecomputePerFunction = 0;
 }
 
 /// NoHonorSignDependentRounding - This predicate is true if support for
 /// sign-dependent-rounding is not enabled.
 def NoHonorSignDependentRounding
  : Predicate<"!TM.Options.HonorSignDependentRoundingFPMath()">;
 
 class Requires<list<Predicate> preds> {

lib/CodeGen/GlobalISel/InstructionSelector.cpp

if (Reg == 0)
       continue;
 
     // If the operand is a vreg, we should constrain its regclass, and only
     // insert COPYs if that's impossible.
     // constrainOperandRegClass does that for us.
     MO.setReg(constrainOperandRegClass(MF, TRI, MRI, TII, RBI, I, I.getDesc(),
                                        Reg, OpI));
 
-    // Tie uses to defs as indicated in MCInstrDesc.
+    // Tie uses to defs as indicated in MCInstrDesc if this hasn't already been
+    // done.
     if (MO.isUse()) {
       int DefIdx = I.getDesc().getOperandConstraint(OpI, MCOI::TIED_TO);
-      if (DefIdx != -1)
+      if (DefIdx != -1 && !I.isRegTiedToUseOperand(DefIdx))
         I.tieOperands(DefIdx, OpI);
     }
   }
   return true;
 }
 
 bool InstructionSelector::isOperandImmEqual(
     const MachineOperand &MO, int64_t Value,

lib/Target/AArch64/AArch64InstrInfo.td

 
 //===----------------------------------------------------------------------===//
 
 //===----------------------------------------------------------------------===//
 
 // AArch64 Instruction Predicate Definitions.
 def IsDarwin  : Predicate<"Subtarget->isTargetDarwin()">;
 def IsNotDarwin: Predicate<"!Subtarget->isTargetDarwin()">;
-def ForCodeSize   : Predicate<"ForCodeSize">;
-def NotForCodeSize   : Predicate<"!ForCodeSize">;
+def ForCodeSize   : Predicate<"Subtarget->getForCodeSize()">;
+def NotForCodeSize   : Predicate<"!Subtarget->getForCodeSize()">;
 
 include "AArch64InstrFormats.td"
 
 //===----------------------------------------------------------------------===//
 
 //===----------------------------------------------------------------------===//
 // Miscellaneous instructions.
 //===----------------------------------------------------------------------===//

lib/Target/AArch64/AArch64InstructionSelector.cpp

 #include "AArch64GenGlobalISel.inc"
 #undef GET_GLOBALISEL_PREDICATE_BITSET
 
 class AArch64InstructionSelector : public InstructionSelector {
 public:
   AArch64InstructionSelector(const AArch64TargetMachine &TM,
                              const AArch64Subtarget &STI,
                              const AArch64RegisterBankInfo &RBI);
 
-  void beginFunction(const MachineFunction &MF) override;
   bool select(MachineInstr &I) const override;
 
 private:
   /// tblgen-erated 'select' implementation, used as the initial selector for
   /// the patterns that don't require complex C++.
   bool selectImpl(MachineInstr &I) const;
 
   bool selectVaStartAAPCS(MachineInstr &I, MachineFunction &MF,
                           MachineRegisterInfo &MRI) const;
   bool selectVaStartDarwin(MachineInstr &I, MachineFunction &MF,
                            MachineRegisterInfo &MRI) const;
 
   bool selectCompareBranch(MachineInstr &I, MachineFunction &MF,
                            MachineRegisterInfo &MRI) const;
 
   ComplexRendererFn selectArithImmed(MachineOperand &Root) const;
 
   const AArch64TargetMachine &TM;
   const AArch64Subtarget &STI;
   const AArch64InstrInfo &TII;
   const AArch64RegisterInfo &TRI;
   const AArch64RegisterBankInfo &RBI;
-  bool ForCodeSize;
 
-  PredicateBitset AvailableFeatures;
-  PredicateBitset
-  computeAvailableFeatures(const MachineFunction *MF,
-                           const AArch64Subtarget *Subtarget) const;
+#define GET_GLOBALISEL_PREDICATES_DECL
+#include "AArch64GenGlobalISel.inc"
+#undef GET_GLOBALISEL_PREDICATES_DECL
 
 // We declare the temporaries used by selectImpl() in the class to minimize the
 // cost of constructing placeholder values.
 #define GET_GLOBALISEL_TEMPORARIES_DECL
 #include "AArch64GenGlobalISel.inc"
 #undef GET_GLOBALISEL_TEMPORARIES_DECL
 };
 
 } // end anonymous namespace
 
 #define GET_GLOBALISEL_IMPL
 #include "AArch64GenGlobalISel.inc"
 #undef GET_GLOBALISEL_IMPL
 
 AArch64InstructionSelector::AArch64InstructionSelector(
     const AArch64TargetMachine &TM, const AArch64Subtarget &STI,
     const AArch64RegisterBankInfo &RBI)
     : InstructionSelector(), TM(TM), STI(STI), TII(*STI.getInstrInfo()),
-      TRI(*STI.getRegisterInfo()), RBI(RBI), ForCodeSize(), AvailableFeatures()
+      TRI(*STI.getRegisterInfo()), RBI(RBI),
+#define GET_GLOBALISEL_PREDICATES_INIT
+#include "AArch64GenGlobalISel.inc"
+#undef GET_GLOBALISEL_PREDICATES_INIT
 #define GET_GLOBALISEL_TEMPORARIES_INIT
 #include "AArch64GenGlobalISel.inc"
 #undef GET_GLOBALISEL_TEMPORARIES_INIT
 {
 }
 
 // FIXME: This should be target-independent, inferred from the types declared
 // for each class in the bank.
MIB = BuildMI(*I.getParent(), I, I.getDebugLoc(), TII.get(AArch64::STRXui))
             .addImm(0)
             .addMemOperand(*I.memoperands_begin());
 
   constrainSelectedInstRegOperands(*MIB, TII, TRI, RBI);
   I.eraseFromParent();
   return true;
 }
 
-void AArch64InstructionSelector::beginFunction(
-    const MachineFunction &MF) {
-  ForCodeSize = MF.getFunction()->optForSize();
-  AvailableFeatures = computeAvailableFeatures(&MF, &STI);
-}
-
 bool AArch64InstructionSelector::select(MachineInstr &I) const {
   assert(I.getParent() && "Instruction should be in a basic block!");
   assert(I.getParent()->getParent() && "Instruction should be in a function!");
 
   MachineBasicBlock &MBB = *I.getParent();
   MachineFunction &MF = *MBB.getParent();
   MachineRegisterInfo &MRI = MF.getRegInfo();
 

lib/Target/AArch64/AArch64Subtarget.h

protected:
   AArch64InstrInfo InstrInfo;
   AArch64SelectionDAGInfo TSInfo;
   AArch64TargetLowering TLInfo;
   /// Gather the accessor points to GlobalISel-related APIs.
   /// This is used to avoid ifndefs spreading around while GISel is
   /// an optional library.
   std::unique_ptr<GISelAccessor> GISel;
 
+  bool ForCodeSize;
+
 private:
   /// initializeSubtargetDependencies - Initializes using CPUString and the
   /// passed in feature string so that we can use initializer lists for
   /// subtarget initialization.
   AArch64Subtarget &initializeSubtargetDependencies(StringRef FS,
                                                     StringRef CPUString);
 
   /// Initialize properties based on the selected processor family.
   void initializeProperties();
 
 public:
   /// This constructor initializes the data members to match that
   /// of the specified triple.
   AArch64Subtarget(const Triple &TT, const std::string &CPU,
                    const std::string &FS, const TargetMachine &TM,
-                   bool LittleEndian);
+                   bool LittleEndian, bool ForCodeSize);
 
   /// This object will take onwership of \p GISelAccessor.
   void setGISelAccessor(GISelAccessor &GISel) {
     this->GISel.reset(&GISel);
   }
 
   const AArch64SelectionDAGInfo *getSelectionDAGInfo() const override {
     return &TSInfo;
switch (TLInfo.getTargetMachine().getCodeModel()) {
         // where it is the same as Small for almost all purposes.
       case CodeModel::Small:
         return true;
       default:
         return false;
     }
   }
 
+  bool getForCodeSize() const { return ForCodeSize; }
+
   /// ParseSubtargetFeatures - Parses features string setting specified
   /// subtarget options.  Definition of function is auto generated by tblgen.
   void ParseSubtargetFeatures(StringRef CPU, StringRef FS);
 
   /// ClassifyGlobalReference - Find the target operand flags that describe
   /// how a global value should be referenced for the current subtarget.
   unsigned char ClassifyGlobalReference(const GlobalValue *GV,
                                         const TargetMachine &TM) const;

lib/Target/AArch64/AArch64Subtarget.cpp

void AArch64Subtarget::initializeProperties() {
   case CortexA72: break;
   case CortexA73: break;
   case Others: break;
   }
 }
 
 AArch64Subtarget::AArch64Subtarget(const Triple &TT, const std::string &CPU,
                                    const std::string &FS,
-                                   const TargetMachine &TM, bool LittleEndian)
+                                   const TargetMachine &TM, bool LittleEndian,
+                                   bool ForCodeSize)
     : AArch64GenSubtargetInfo(TT, CPU, FS), ReserveX18(TT.isOSDarwin()),
       IsLittle(LittleEndian), TargetTriple(TT), FrameLowering(),
       InstrInfo(initializeSubtargetDependencies(FS, CPU)), TSInfo(),
-      TLInfo(TM, *this), GISel() {}
+      TLInfo(TM, *this), GISel(), ForCodeSize(ForCodeSize) {}
 
 const CallLowering *AArch64Subtarget::getCallLowering() const {
   assert(GISel && "Access to GlobalISel APIs not set");
   return GISel->getCallLowering();
 }
 
 const InstructionSelector *AArch64Subtarget::getInstructionSelector() const {
   assert(GISel && "Access to GlobalISel APIs not set");

lib/Target/AArch64/AArch64TargetMachine.cpp

 
 } // end anonymous namespace
 #endif
 
 const AArch64Subtarget *
 AArch64TargetMachine::getSubtargetImpl(const Function &F) const {
   Attribute CPUAttr = F.getFnAttribute("target-cpu");
   Attribute FSAttr = F.getFnAttribute("target-features");
+  bool ForCodeSize = F.optForSize();
 
   std::string CPU = !CPUAttr.hasAttribute(Attribute::None)
                         ? CPUAttr.getValueAsString().str()
                         : TargetCPU;
   std::string FS = !FSAttr.hasAttribute(Attribute::None)
                        ? FSAttr.getValueAsString().str()
                        : TargetFS;
+  std::string ForCodeSizeStr =
+      std::string(ForCodeSize ? "+" : "-") + "forcodesize";
 
-  auto &I = SubtargetMap[CPU + FS];
+  auto &I = SubtargetMap[CPU + FS + ForCodeSizeStr];
   if (!I) {
     // This needs to be done before we create a new subtarget since any
     // creation will depend on the TM and the code generation flags on the
     // function that reside in TargetOptions.
     resetTargetOptions(F);
     I = llvm::make_unique<AArch64Subtarget>(TargetTriple, CPU, FS, *this,
-                                            isLittle);
+                                            isLittle, ForCodeSize);
 #ifndef LLVM_BUILD_GLOBAL_ISEL
     GISelAccessor *GISel = new GISelAccessor();
 #else
     AArch64GISelActualAccessor *GISel =
         new AArch64GISelActualAccessor();
     GISel->CallLoweringInfo.reset(
         new AArch64CallLowering(*I->getTargetLowering()));
     GISel->Legalizer.reset(new AArch64LegalizerInfo());

lib/Target/X86/X86InstrInfo.td

def In16BitMode  : Predicate<"Subtarget->is16Bit()">,
                              AssemblerPredicate<"Mode16Bit", "16-bit mode">;
 def Not16BitMode : Predicate<"!Subtarget->is16Bit()">,
                              AssemblerPredicate<"!Mode16Bit", "Not 16-bit mode">;
 def In32BitMode  : Predicate<"Subtarget->is32Bit()">,
                              AssemblerPredicate<"Mode32Bit", "32-bit mode">;
 def IsWin64      : Predicate<"Subtarget->isTargetWin64()">;
 def NotWin64     : Predicate<"!Subtarget->isTargetWin64()">;
 def NotWin64WithoutFP : Predicate<"!Subtarget->isTargetWin64() ||"
-                                  "Subtarget->getFrameLowering()->hasFP(*MF)">;
+                                  "Subtarget->getFrameLowering()->hasFP(*MF)"> {
+  let RecomputePerFunction = 1;
+}
 def IsPS4        : Predicate<"Subtarget->isTargetPS4()">;
 def NotPS4       : Predicate<"!Subtarget->isTargetPS4()">;
 def IsNaCl       : Predicate<"Subtarget->isTargetNaCl()">;
 def NotNaCl      : Predicate<"!Subtarget->isTargetNaCl()">;
 def SmallCode    : Predicate<"TM.getCodeModel() == CodeModel::Small">;
 def KernelCode   : Predicate<"TM.getCodeModel() == CodeModel::Kernel">;
 def NearData     : Predicate<"TM.getCodeModel() == CodeModel::Small ||"
                              "TM.getCodeModel() == CodeModel::Kernel">;
 def IsNotPIC     : Predicate<"!TM.isPositionIndependent()">;
-def OptForSize   : Predicate<"OptForSize">;
-def OptForMinSize : Predicate<"OptForMinSize">;
-def OptForSpeed  : Predicate<"!OptForSize">;
+def OptForSize   : Predicate<"Subtarget->getOptForSize()">;
+def OptForMinSize : Predicate<"Subtarget->getOptForMinSize()">;
+def OptForSpeed  : Predicate<"!Subtarget->getOptForSize()">;
 def FastBTMem    : Predicate<"!Subtarget->isBTMemSlow()">;
 def CallImmAddr  : Predicate<"Subtarget->isLegalToCallImmediateAddr()">;
 def FavorMemIndirectCall  : Predicate<"!Subtarget->callRegIndirect()">;
 def NotSlowIncDec : Predicate<"!Subtarget->slowIncDec()">;
 def HasFastMem32 : Predicate<"!Subtarget->isUnalignedMem32Slow()">;
 def HasFastLZCNT : Predicate<"Subtarget->hasFastLZCNT()">;
 def HasFastSHLDRotate : Predicate<"Subtarget->hasFastSHLDRotate()">;
 def HasERMSB : Predicate<"Subtarget->hasERMSB()">;

lib/Target/X86/X86InstructionSelector.cpp

 #include "X86GenGlobalISel.inc"
 #undef GET_GLOBALISEL_PREDICATE_BITSET
 
 class X86InstructionSelector : public InstructionSelector {
 public:
   X86InstructionSelector(const X86TargetMachine &TM, const X86Subtarget &STI,
                          const X86RegisterBankInfo &RBI);
 
-  void beginFunction(const MachineFunction &MF) override;
   bool select(MachineInstr &I) const override;
 
 private:
   /// tblgen-erated 'select' implementation, used as the initial selector for
   /// the patterns that don't require complex C++.
   bool selectImpl(MachineInstr &I) const;
 
   // TODO: remove after selectImpl support pattern with a predicate.
private:
   bool selectTrunc(MachineInstr &I, MachineRegisterInfo &MRI,
                    MachineFunction &MF) const;
 
   const X86TargetMachine &TM;
   const X86Subtarget &STI;
   const X86InstrInfo &TII;
   const X86RegisterInfo &TRI;
   const X86RegisterBankInfo &RBI;
-  bool OptForSize;
-  bool OptForMinSize;
 
-  PredicateBitset AvailableFeatures;
-  PredicateBitset computeAvailableFeatures(const MachineFunction *MF,
-                                           const X86Subtarget *Subtarget) const;
+#define GET_GLOBALISEL_PREDICATES_DECL
+#include "X86GenGlobalISel.inc"
+#undef GET_GLOBALISEL_PREDICATES_DECL
 
 #define GET_GLOBALISEL_TEMPORARIES_DECL
 #include "X86GenGlobalISel.inc"
 #undef GET_GLOBALISEL_TEMPORARIES_DECL
 };
 
 } // end anonymous namespace
 
 #define GET_GLOBALISEL_IMPL
 #include "X86GenGlobalISel.inc"
 #undef GET_GLOBALISEL_IMPL
 
 X86InstructionSelector::X86InstructionSelector(const X86TargetMachine &TM,
                                                const X86Subtarget &STI,
                                                const X86RegisterBankInfo &RBI)
     : InstructionSelector(), TM(TM), STI(STI), TII(*STI.getInstrInfo()),
-      TRI(*STI.getRegisterInfo()), RBI(RBI), OptForSize(false),
-      OptForMinSize(false), AvailableFeatures()
+      TRI(*STI.getRegisterInfo()), RBI(RBI),
+#define GET_GLOBALISEL_PREDICATES_INIT
+#include "X86GenGlobalISel.inc"
+#undef GET_GLOBALISEL_PREDICATES_INIT
 #define GET_GLOBALISEL_TEMPORARIES_INIT
 #include "X86GenGlobalISel.inc"
 #undef GET_GLOBALISEL_TEMPORARIES_INIT
 {
 }
 
 // FIXME: This should be target-independent, inferred from the types declared
 // for each class in the bank.
if (!RBI.constrainGenericRegister(DstReg, *RC, MRI)) {
                    << " operand\n");
       return false;
     }
   }
   I.setDesc(TII.get(X86::COPY));
   return true;
 }
 
-void X86InstructionSelector::beginFunction(const MachineFunction &MF) {
-  OptForSize = MF.getFunction()->optForSize();
-  OptForMinSize = MF.getFunction()->optForMinSize();
-  AvailableFeatures = computeAvailableFeatures(&MF, &STI);
-}
-
 bool X86InstructionSelector::select(MachineInstr &I) const {
   assert(I.getParent() && "Instruction should be in a basic block!");
   assert(I.getParent()->getParent() && "Instruction should be in a function!");
 
   MachineBasicBlock &MBB = *I.getParent();
   MachineFunction &MF = *MBB.getParent();
   MachineRegisterInfo &MRI = MF.getRegInfo();
 

lib/Target/X86/X86Subtarget.h

private:
 
   X86SelectionDAGInfo TSInfo;
   // Ordering here is important. X86InstrInfo initializes X86RegisterInfo which
   // X86TargetLowering needs.
   X86InstrInfo InstrInfo;
   X86TargetLowering TLInfo;
   X86FrameLowering FrameLowering;
 
+  bool OptForSize;
+  bool OptForMinSize;
+
 public:
   /// This constructor initializes the data members to match that
   /// of the specified triple.
   ///
   X86Subtarget(const Triple &TT, StringRef CPU, StringRef FS,
-               const X86TargetMachine &TM, unsigned StackAlignOverride);
+               const X86TargetMachine &TM, unsigned StackAlignOverride,
+               bool OptForSize, bool OptForMinSize);
 
   /// This object will take onwership of \p GISelAccessor.
   void setGISelAccessor(GISelAccessor &GISel) { this->GISel.reset(&GISel); }
 
   const X86TargetLowering *getTargetLowering() const override {
     return &TLInfo;
   }
 
public:
   bool hasCLFLUSHOPT() const { return HasCLFLUSHOPT; }
 
   bool isXRaySupported() const override { return is64Bit(); }
 
   bool isAtom() const { return X86ProcFamily == IntelAtom; }
   bool isSLM() const { return X86ProcFamily == IntelSLM; }
   bool useSoftFloat() const { return UseSoftFloat; }
 
+  bool getOptForSize() const { return OptForSize; }
+  bool getOptForMinSize() const { return OptForMinSize; }
+
   /// Use mfence if we have SSE2 or we're on x86-64 (even if we asked for
   /// no-sse2). There isn't any reason to disable it if the target processor
   /// supports it.
   bool hasMFence() const { return hasSSE2() || is64Bit(); }
 
   const Triple &getTargetTriple() const { return TargetTriple; }
 
   bool isTargetDarwin() const { return TargetTriple.isOSDarwin(); }

lib/Target/X86/X86Subtarget.cpp

X86Subtarget &X86Subtarget::initializeSubtargetDependencies(StringRef CPU,
                                                             StringRef FS) {
   initializeEnvironment();
   initSubtargetFeatures(CPU, FS);
   return *this;
 }
 
 X86Subtarget::X86Subtarget(const Triple &TT, StringRef CPU, StringRef FS,
                            const X86TargetMachine &TM,
-                           unsigned StackAlignOverride)
+                           unsigned StackAlignOverride, bool OptForSize,
+                           bool OptForMinSize)
     : X86GenSubtargetInfo(TT, CPU, FS), X86ProcFamily(Others),
       PICStyle(PICStyles::None), TM(TM), TargetTriple(TT),
       StackAlignOverride(StackAlignOverride),
       In64BitMode(TargetTriple.getArch() == Triple::x86_64),
       In32BitMode(TargetTriple.getArch() == Triple::x86 &&
                   TargetTriple.getEnvironment() != Triple::CODE16),
       In16BitMode(TargetTriple.getArch() == Triple::x86 &&
                   TargetTriple.getEnvironment() == Triple::CODE16),
-      InstrInfo(initializeSubtargetDependencies(CPU, FS)),
-      TLInfo(TM, *this), FrameLowering(*this, getStackAlignment()) {
+      InstrInfo(initializeSubtargetDependencies(CPU, FS)), TLInfo(TM, *this),
+      FrameLowering(*this, getStackAlignment()), OptForSize(OptForSize),
+      OptForMinSize(OptForMinSize) {
   // Determine the PICStyle based on the target selected.
   if (!isPositionIndependent())
     setPICStyle(PICStyles::None);
   else if (is64Bit())
     setPICStyle(PICStyles::RIPRel);
   else if (isTargetCOFF())
     setPICStyle(PICStyles::None);
   else if (isTargetDarwin())

lib/Target/X86/X86TargetMachine.cpp

bool SoftFloat =
       F.getFnAttribute("use-soft-float").getValueAsString() == "true";
   // If the soft float attribute is set on the function turn on the soft float
   // subtarget feature.
   if (SoftFloat)
     Key += FS.empty() ? "+soft-float" : ",+soft-float";
 
   FS = Key.substr(CPU.size());
 
+  bool OptForSize = F.optForSize();
+  bool OptForMinSize = F.optForMinSize();
+
+  Key += std::string(OptForSize ? "+" : "-") + "optforsize";
+  Key += std::string(OptForMinSize ? "+" : "-") + "optforminsize";
+
   auto &I = SubtargetMap[Key];
   if (!I) {
     // This needs to be done before we create a new subtarget since any
     // creation will depend on the TM and the code generation flags on the
     // function that reside in TargetOptions.
     resetTargetOptions(F);
     I = llvm::make_unique<X86Subtarget>(TargetTriple, CPU, FS, *this,
-                                        Options.StackAlignmentOverride);
+                                        Options.StackAlignmentOverride,
+                                        OptForSize, OptForMinSize);
 #ifndef LLVM_BUILD_GLOBAL_ISEL
     GISelAccessor *GISel = new GISelAccessor();
 #else
     X86GISelActualAccessor *GISel = new X86GISelActualAccessor();
 
     GISel->CallLoweringInfo.reset(new X86CallLowering(*I->getTargetLowering()));
     GISel->Legalizer.reset(new X86LegalizerInfo(*I, *this));
 
     auto *RBI = new X86RegisterBankInfo(*I->getRegisterInfo());
     GISel->RegBankInfo.reset(RBI);
-    GISel->InstSelector.reset(createX86InstructionSelector(*this, *I, *RBI));
+    GISel->InstSelector.reset(createX86InstructionSelector(
+        *this, *I, *RBI));
 #endif
     I->setGISelAccessor(*GISel);
   }
   return I.get();
 }
 
 //===----------------------------------------------------------------------===//
 // Command line options for x86

test/CodeGen/X86/GlobalISel/select-inc.mir

+# RUN: llc -mtriple=x86_64-linux-gnu                     -global-isel -run-pass=instruction-select -verify-machineinstrs %s -o - | FileCheck %s --check-prefixes=ALL,INC
+# RUN: llc -mtriple=x86_64-linux-gnu -mattr=+slow-incdec -global-isel -run-pass=instruction-select -verify-machineinstrs %s -o - | FileCheck %s --check-prefixes=ALL,ADD
+
+--- |
+  define i8 @test_add_i8(i8 %arg1) {
+    %ret = add i8 %arg1, 1
+    ret i8 %ret
+  }
+...
+
+---
+name:            test_add_i8
+legalized:       true
+regBankSelected: true
+# ALL:      registers:
+# ALL-NEXT:  - { id: 0, class: gr8 }
+# INC-NEXT:  - { id: 1, class: gpr }
+# ADD-NEXT:  - { id: 1, class: gr8 }
+# ALL-NEXT:  - { id: 2, class: gr8 }
+registers:
+  - { id: 0, class: gpr }
+  - { id: 1, class: gpr }
+  - { id: 2, class: gpr }
+# ALL:      %0 = COPY %al
+# INC-NEXT: %2 = INC8r %0
+# ADD-NEXT: %1 = MOV8ri 1
+# ADD-NEXT: %2 = ADD8rr %0, %1
+body:             |
+  bb.1 (%ir-block.0):
+    liveins: %al
+
+    %0(s8) = COPY %al
+    %1(s8) = G_CONSTANT i8 1
+    %2(s8) = G_ADD %0, %1
+    %al = COPY %2(s8)
+
+...

test/TableGen/GlobalISelEmitter.td

def gi_complex :
     GIComplexPatternEquiv<complex>;
 
 def m1 : OperandWithDefaultOps <i32, (ops (i32 -1))>;
 def Z : OperandWithDefaultOps <i32, (ops R0)>;
 def m1Z : OperandWithDefaultOps <i32, (ops (i32 -1), R0)>;
 
 def HasA : Predicate<"Subtarget->hasA()">;
 def HasB : Predicate<"Subtarget->hasB()">;
+def HasC : Predicate<"Subtarget->hasC()"> { let RecomputePerFunction = 1; }
 
 //===- Test the function boilerplate. -------------------------------------===//
 
 // CHECK-LABEL: enum SubtargetFeatureBits : uint8_t {
 // CHECK-NEXT:    Feature_HasABit = 0,
 // CHECK-NEXT:    Feature_HasBBit = 1,
+// CHECK-NEXT:    Feature_HasCBit = 2,
 // CHECK-NEXT:  };
 
 // CHECK-LABEL: static const char *SubtargetFeatureNames[] = {
 // CHECK-NEXT:    "Feature_HasA",
 // CHECK-NEXT:    "Feature_HasB",
+// CHECK-NEXT:    "Feature_HasC",
 // CHECK-NEXT:    nullptr
 // CHECK-NEXT:  };
 
 // CHECK-LABEL: PredicateBitset MyTargetInstructionSelector::
-// CHECK-NEXT:  computeAvailableFeatures(const MachineFunction *MF, const MyTargetSubtarget *Subtarget) const {
+// CHECK-NEXT:  computeAvailableModuleFeatures(const MyTargetSubtarget *Subtarget) const {
 // CHECK-NEXT:    PredicateBitset Features;
 // CHECK-NEXT:    if (Subtarget->hasA())
 // CHECK-NEXT:      Features[Feature_HasABit] = 1;
 // CHECK-NEXT:    if (Subtarget->hasB())
 // CHECK-NEXT:      Features[Feature_HasBBit] = 1;
 // CHECK-NEXT:    return Features;
 // CHECK-NEXT:  }
 
+// CHECK-LABEL: PredicateBitset MyTargetInstructionSelector::
+// CHECK-NEXT:  computeAvailableFunctionFeatures(const MyTargetSubtarget *Subtarget, const MachineFunction *MF) const {
+// CHECK-NEXT:    PredicateBitset Features;
+// CHECK-NEXT:    if (Subtarget->hasC())
+// CHECK-NEXT:      Features[Feature_HasCBit] = 1;
+// CHECK-NEXT:    return Features;
+// CHECK-NEXT:  }
+
 // CHECK: bool MyTargetInstructionSelector::selectImpl(MachineInstr &I) const {
 // CHECK: MachineFunction &MF = *I.getParent()->getParent();
 // CHECK: const MachineRegisterInfo &MRI = MF.getRegInfo();
 
 //===- Test a pattern with multiple ComplexPattern operands. --------------===//
 //
 
 // CHECK-LABEL: if ([&]() {

 def MULADD : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2, GPR32:$src3),
                [(set GPR32:$dst,
                      (mul (add GPR32:$src1, GPR32:$src2), GPR32:$src3))]>,
              Requires<[HasA]>;
 
 //===- Test another simple pattern with regclass operands. ----------------===//
 
 // CHECK-LABEL: if ([&]() {
-// CHECK-NEXT:    PredicateBitset ExpectedFeatures = {Feature_HasABit, Feature_HasBBit};
+// CHECK-NEXT:    PredicateBitset ExpectedFeatures = {Feature_HasABit, Feature_HasBBit, Feature_HasCBit};
 // CHECK-NEXT:    if ((AvailableFeatures & ExpectedFeatures) != ExpectedFeatures)
 // CHECK-NEXT:      return false;
 // CHECK-NEXT:    MachineInstr &MI0 = I;
 // CHECK-NEXT:    if (MI0.getNumOperands() < 3)
 // CHECK-NEXT:      return false;
 // CHECK-NEXT:    if ((MI0.getOpcode() == TargetOpcode::G_MUL) &&
 // CHECK-NEXT:        ((/* dst */ (MRI.getType(MI0.getOperand(0).getReg()) == (LLT::scalar(32))) &&
 // CHECK-NEXT:         ((&RBI.getRegBankFromRegClass(MyTarget::GPR32RegClass) == RBI.getRegBank(MI0.getOperand(0).getReg(), MRI, TRI))))) &&

 // CHECK-NEXT:      constrainSelectedInstRegOperands(NewI, TII, TRI, RBI);
 // CHECK-NEXT:      return true;
 // CHECK-NEXT:    }
 // CHECK-NEXT:    return false;
 // CHECK-NEXT:  }()) { return true; }
 
 def MUL : I<(outs GPR32:$dst), (ins GPR32:$src2, GPR32:$src1),
              [(set GPR32:$dst, (mul GPR32:$src1, GPR32:$src2))]>,
-          Requires<[HasA, HasB]>;
+          Requires<[HasA, HasB, HasC]>;
 
 //===- Test a pattern with ComplexPattern operands. -----------------------===//
 //
 
 // CHECK-LABEL: if ([&]() {
 // CHECK-NEXT:    MachineInstr &MI0 = I;
 // CHECK-NEXT:    if (MI0.getNumOperands() < 3)
 // CHECK-NEXT:      return false;

unittests/Target/AArch64/InstSizes.cpp

std::unique_ptr<TargetMachine> createTargetMachine() {
 
   return std::unique_ptr<TargetMachine>(
       TheTarget->createTargetMachine(TT, CPU, FS, TargetOptions(), None,
                                      CodeModel::Default, CodeGenOpt::Default));
 }
 
 std::unique_ptr<AArch64InstrInfo> createInstrInfo(TargetMachine *TM) {
   AArch64Subtarget ST(TM->getTargetTriple(), TM->getTargetCPU(),
-                      TM->getTargetFeatureString(), *TM, /* isLittle */ false);
+                      TM->getTargetFeatureString(), *TM, /* isLittle */ false,
+                      /* ForCodeSize */ false);
   return llvm::make_unique<AArch64InstrInfo>(ST);
 }
 
 /// The \p InputIRSnippet is only needed for things that can't be expressed in
 /// the \p InputMIRSnippet (global variables etc)
 /// TODO: Some of this might be useful for other architectures as well - extract
 ///       the platform-independent parts somewhere they can be reused.
 void runChecks(

utils/TableGen/GlobalISelEmitter.cpp

public:
 
   std::string defineInsnVar(raw_ostream &OS, const InstructionMatcher &Matcher,
                             StringRef Value);
   StringRef getInsnVarName(const InstructionMatcher &InsnMatcher) const;
 
   void emitCxxCapturedInsnList(raw_ostream &OS);
   void emitCxxCaptureStmts(raw_ostream &OS, StringRef Expr);
 
-  void emit(raw_ostream &OS,
-            std::map<Record *, SubtargetFeatureInfo, LessRecordByID>
-                SubtargetFeatures);
+void emit(raw_ostream &OS, SubtargetFeatureInfoMap SubtargetFeatures);
 
-  /// Compare the priority of this object and B.
-  ///
-  /// Returns true if this object is more important than B.
-  bool isHigherPriorityThan(const RuleMatcher &B) const;
 
-  /// Report the maximum number of temporary operands needed by the rule
-  /// matcher.
-  unsigned countRendererFns() const;
 
-  // FIXME: Remove this as soon as possible
-  InstructionMatcher &insnmatcher_front() const { return *Matchers.front(); }
 };
 
 template <class PredicateTy> class PredicateListMatcher {
 private:
   typedef std::vector<std::unique_ptr<PredicateTy>> PredicateVec;
   PredicateVec Predicates;
 
 public:

 class BuildMIAction : public MatchAction {
 private:
   const CodeGenInstruction *I;
   const InstructionMatcher &Matched;
   std::vector<std::unique_ptr<OperandRenderer>> OperandRenderers;
 
   /// True if the instruction can be built solely by mutating the opcode.
   bool canMutate() const {
+    if (OperandRenderers.size() != Matched.getNumOperands())
+      return false;
+
     for (const auto &Renderer : enumerate(OperandRenderers)) {
       if (const auto *Copy = dyn_cast<CopyRenderer>(&*Renderer.value())) {
         const OperandMatcher &OM = Matched.getOperand(Copy->getSymbolicName());
         if (&Matched != &OM.getInstructionMatcher() ||
             OM.getOperandIndex() != Renderer.index())
           return false;
       } else
         return false;

 /// instructions into local variables.
 void RuleMatcher::emitCxxCaptureStmts(raw_ostream &OS, StringRef Expr) {
   assert(Matchers.size() == 1 && "Cannot handle multi-root matchers yet");
   std::string InsnVarName = defineInsnVar(OS, *Matchers.front(), Expr);
   Matchers.front()->emitCxxCaptureStmts(OS, *this, InsnVarName);
 }
 
 void RuleMatcher::emit(raw_ostream &OS,
-                       std::map<Record *, SubtargetFeatureInfo, LessRecordByID>
-                           SubtargetFeatures) {
+                       SubtargetFeatureInfoMap SubtargetFeatures) {
   if (Matchers.empty())
     llvm_unreachable("Unexpected empty matcher!");
 
   // The representation supports rules that require multiple roots such as:
   //    %ptr(p0) = ...
   //    %elt0(s32) = G_LOAD %ptr
   //    %1(p0) = G_ADD %ptr, 4
   //    %elt1(s32) = G_LOAD p0 %1
private:
   DenseMap<Record *, const CodeGenInstruction *> NodeEquivs;
 
   /// Keep track of the equivalence between ComplexPattern's and
   /// GIComplexOperandMatcher. Map entries are specified by subclassing
   /// GIComplexPatternEquiv.
   DenseMap<const Record *, const Record *> ComplexPatternEquivs;
 
   // Map of predicates to their subtarget features.
-  std::map<Record *, SubtargetFeatureInfo, LessRecordByID> SubtargetFeatures;
+  SubtargetFeatureInfoMap SubtargetFeatures;
 
   void gatherNodeEquivs();
   const CodeGenInstruction *findNodeEquiv(Record *N) const;
 
   Error importRulePredicates(RuleMatcher &M, ArrayRef<Init *> Predicates);
   Expected<InstructionMatcher &>
   createAndImportSelDAGMatcher(InstructionMatcher &InsnMatcher,
                                const TreePatternNode *Src) const;
void GlobalISelEmitter::run(raw_ostream &OS) {
   for (unsigned I = 0; I < MaxTemporaries; ++I)
     OS << ", Renderer" << I << "(nullptr)\n";
   OS << "#endif // ifdef GET_GLOBALISEL_TEMPORARIES_INIT\n\n";
 
   OS << "#ifdef GET_GLOBALISEL_IMPL\n";
   SubtargetFeatureInfo::emitSubtargetFeatureBitEnumeration(SubtargetFeatures,
                                                            OS);
   SubtargetFeatureInfo::emitNameTable(SubtargetFeatures, OS);
+
+  // Separate subtarget features by how often they must be recomputed.
+  SubtargetFeatureInfoMap ModuleFeatures;
+  std::copy_if(SubtargetFeatures.begin(), SubtargetFeatures.end(),
+               std::inserter(ModuleFeatures, ModuleFeatures.end()),
+               [](const SubtargetFeatureInfoMap::value_type &X) {
+                 return !X.second.mustRecomputePerFunction();
+               });
+  SubtargetFeatureInfoMap FunctionFeatures;
+  std::copy_if(SubtargetFeatures.begin(), SubtargetFeatures.end(),
+               std::inserter(FunctionFeatures, FunctionFeatures.end()),
+               [](const SubtargetFeatureInfoMap::value_type &X) {
+                 return X.second.mustRecomputePerFunction();
+               });
+
+  SubtargetFeatureInfo::emitComputeAvailableFeatures(
+      Target.getName(), "InstructionSelector", "computeAvailableModuleFeatures",
+      ModuleFeatures, OS);
   SubtargetFeatureInfo::emitComputeAvailableFeatures(
-      Target.getName(), "InstructionSelector", "computeAvailableFeatures",
-      SubtargetFeatures, OS);
+      Target.getName(), "InstructionSelector",
+      "computeAvailableFunctionFeatures", FunctionFeatures, OS,
+      "const MachineFunction *MF");
 
   OS << "bool " << Target.getName()
      << "InstructionSelector::selectImpl(MachineInstr &I) const {\n"
      << "  MachineFunction &MF = *I.getParent()->getParent();\n"
-     << "  const MachineRegisterInfo &MRI = MF.getRegInfo();\n";
+     << "  const MachineRegisterInfo &MRI = MF.getRegInfo();\n"
+     << "  // FIXME: This should be computed on a per-function basis rather than per-insn.\n"
+     << "  AvailableFunctionFeatures = computeAvailableFunctionFeatures(&STI, &MF);\n"
+     << "  const PredicateBitset AvailableFeatures = getAvailableFeatures();\n";
 
   for (auto &Rule : Rules) {
     Rule.emit(OS, SubtargetFeatures);
     ++NumPatternEmitted;
   }
 
   OS << "  return false;\n"
      << "}\n"
      << "#endif // ifdef GET_GLOBALISEL_IMPL\n";
+
+  OS << "#ifdef GET_GLOBALISEL_PREDICATES_DECL\n"
+     << "PredicateBitset AvailableModuleFeatures;\n"
+     << "mutable PredicateBitset AvailableFunctionFeatures;\n"
+     << "PredicateBitset getAvailableFeatures() const {\n"
+     << "  return AvailableModuleFeatures | AvailableFunctionFeatures;\n"
+     << "}\n"
+     << "PredicateBitset\n"
+     << "computeAvailableModuleFeatures(const " << Target.getName()
+     << "Subtarget *Subtarget) const;\n"
+     << "PredicateBitset\n"
+     << "computeAvailableFunctionFeatures(const " << Target.getName()
+     << "Subtarget *Subtarget,\n"
+     << "                                 const MachineFunction *MF) const;\n"
+     << "#endif // ifdef GET_GLOBALISEL_PREDICATES_DECL\n";
+
+  OS << "#ifdef GET_GLOBALISEL_PREDICATES_INIT\n"
+     << "AvailableModuleFeatures(computeAvailableModuleFeatures(&STI)),\n"
+     << "AvailableFunctionFeatures()\n"
+     << "#endif // ifdef GET_GLOBALISEL_PREDICATES_INIT\n";
 }
 
 void GlobalISelEmitter::declareSubtargetFeature(Record *Predicate) {
   if (SubtargetFeatures.count(Predicate) == 0)
     SubtargetFeatures.emplace(
         Predicate, SubtargetFeatureInfo(Predicate, SubtargetFeatures.size()));
 }
 

utils/TableGen/SubtargetFeatureInfo.h

 #include <map>
 #include <string>
 #include <vector>
 
 namespace llvm {
 class Record;
 class RecordKeeper;
 
+struct SubtargetFeatureInfo;
+using SubtargetFeatureInfoMap = std::map<Record *, SubtargetFeatureInfo, LessRecordByID>;
+
 /// Helper class for storing information on a subtarget feature which
 /// participates in instruction matching.
 struct SubtargetFeatureInfo {
   /// \brief The predicate record for this feature.
   Record *TheDef;
 
   /// \brief An unique index assigned to represent this feature.
   uint64_t Index;
 
   SubtargetFeatureInfo(Record *D, uint64_t Idx) : TheDef(D), Index(Idx) {}
 
   /// \brief The name of the enumerated constant identifying this feature.
   std::string getEnumName() const {
     return "Feature_" + TheDef->getName().str();
   }
 
   /// \brief The name of the enumerated constant identifying the bitnumber for
   /// this feature.
   std::string getEnumBitName() const {
     return "Feature_" + TheDef->getName().str() + "Bit";
   }
 
+  bool mustRecomputePerFunction() const {
+    return TheDef->getValueAsBit("RecomputePerFunction");
+  }
+
   void dump() const;
   static std::vector<std::pair<Record *, SubtargetFeatureInfo>>
   getAll(const RecordKeeper &Records);
 
   /// Emit the subtarget feature flag definitions.
   ///
   /// This version emits the bit value for the feature and is therefore limited
   /// to 64 feature bits.
   static void emitSubtargetFeatureFlagEnumeration(
-      std::map<Record *, SubtargetFeatureInfo, LessRecordByID>
-          &SubtargetFeatures,
-      raw_ostream &OS);
+      SubtargetFeatureInfoMap &SubtargetFeatures, raw_ostream &OS);
 
   /// Emit the subtarget feature flag definitions.
   ///
   /// This version emits the bit index for the feature and can therefore support
   /// more than 64 feature bits.
-  static void emitSubtargetFeatureBitEnumeration(
-      std::map<Record *, SubtargetFeatureInfo, LessRecordByID>
-          &SubtargetFeatures,
+  static void
+  emitSubtargetFeatureBitEnumeration(SubtargetFeatureInfoMap &SubtargetFeatures,
                                      raw_ostream &OS);
 
-  static void emitNameTable(std::map<Record *, SubtargetFeatureInfo,
-                                     LessRecordByID> &SubtargetFeatures,
+  static void emitNameTable(SubtargetFeatureInfoMap &SubtargetFeatures,
                             raw_ostream &OS);
 
   /// Emit the function to compute the list of available features given a
   /// subtarget.
   ///
   /// This version is used for subtarget features defined using Predicate<>
   /// and supports more than 64 feature bits.
   ///
   /// \param TargetName The name of the target as used in class prefixes (e.g.
   ///                   <TargetName>Subtarget)
   /// \param ClassName  The name of the class (without the <Target> prefix)
   ///                   that will contain the generated functions.
   /// \param FuncName   The name of the function to emit.
   /// \param SubtargetFeatures A map of TableGen records to the
   ///                          SubtargetFeatureInfo equivalent.
-  static void emitComputeAvailableFeatures(
-      StringRef TargetName, StringRef ClassName, StringRef FuncName,
-      std::map<Record *, SubtargetFeatureInfo, LessRecordByID>
-          &SubtargetFeatures,
-      raw_ostream &OS);
+  /// \param ExtraParams Additional arguments to the generated function.
+  static void
+  emitComputeAvailableFeatures(StringRef TargetName, StringRef ClassName,
+                               StringRef FuncName,
+                               SubtargetFeatureInfoMap &SubtargetFeatures,
+                               raw_ostream &OS, StringRef ExtraParams = "");
 
   /// Emit the function to compute the list of available features given a
   /// subtarget.
   ///
   /// This version is used for subtarget features defined using
   /// AssemblerPredicate<> and supports up to 64 feature bits.
   ///
   /// \param TargetName The name of the target as used in class prefixes (e.g.
   ///                   <TargetName>Subtarget)
   /// \param ClassName  The name of the class (without the <Target> prefix)
   ///                   that will contain the generated functions.
   /// \param FuncName   The name of the function to emit.
   /// \param SubtargetFeatures A map of TableGen records to the
   ///                          SubtargetFeatureInfo equivalent.
   static void emitComputeAssemblerAvailableFeatures(
       StringRef TargetName, StringRef ClassName, StringRef FuncName,
-      std::map<Record *, SubtargetFeatureInfo, LessRecordByID>
-          &SubtargetFeatures,
-      raw_ostream &OS);
+      SubtargetFeatureInfoMap &SubtargetFeatures, raw_ostream &OS);
 };
 } // end namespace llvm
 
 #endif // LLVM_UTIL_TABLEGEN_SUBTARGETFEATUREINFO_H

utils/TableGen/SubtargetFeatureInfo.cpp

for (Record *Pred : AllPredicates) {
 
     SubtargetFeatures.emplace_back(
         Pred, SubtargetFeatureInfo(Pred, SubtargetFeatures.size()));
   }
   return SubtargetFeatures;
 }
 
 void SubtargetFeatureInfo::emitSubtargetFeatureFlagEnumeration(
-    std::map<Record *, SubtargetFeatureInfo, LessRecordByID> &SubtargetFeatures,
-    raw_ostream &OS) {
+    SubtargetFeatureInfoMap &SubtargetFeatures, raw_ostream &OS) {
   OS << "// Flags for subtarget features that participate in "
      << "instruction matching.\n";
   OS << "enum SubtargetFeatureFlag : "
      << getMinimalTypeForEnumBitfield(SubtargetFeatures.size()) << " {\n";
   for (const auto &SF : SubtargetFeatures) {
     const SubtargetFeatureInfo &SFI = SF.second;
     OS << "  " << SFI.getEnumName() << " = (1ULL << " << SFI.Index << "),\n";
   }
   OS << "  Feature_None = 0\n";
   OS << "};\n\n";
 }
 
 void SubtargetFeatureInfo::emitSubtargetFeatureBitEnumeration(
-    std::map<Record *, SubtargetFeatureInfo, LessRecordByID> &SubtargetFeatures,
-    raw_ostream &OS) {
+    SubtargetFeatureInfoMap &SubtargetFeatures, raw_ostream &OS) {
   OS << "// Bits for subtarget features that participate in "
      << "instruction matching.\n";
   OS << "enum SubtargetFeatureBits : "
      << getMinimalTypeForRange(SubtargetFeatures.size()) << " {\n";
   for (const auto &SF : SubtargetFeatures) {
     const SubtargetFeatureInfo &SFI = SF.second;
     OS << "  " << SFI.getEnumBitName() << " = " << SFI.Index << ",\n";
   }
   OS << "};\n\n";
 }
 
 void SubtargetFeatureInfo::emitNameTable(
-    std::map<Record *, SubtargetFeatureInfo, LessRecordByID> &SubtargetFeatures,
-    raw_ostream &OS) {
+    SubtargetFeatureInfoMap &SubtargetFeatures, raw_ostream &OS) {
   // Need to sort the name table so that lookup by the log of the enum value
   // gives the proper name. More specifically, for a feature of value 1<<n,
   // SubtargetFeatureNames[n] should be the name of the feature.
   uint64_t IndexUB = 0;
   for (const auto &SF : SubtargetFeatures)
     if (IndexUB <= SF.second.Index)
       IndexUB = SF.second.Index+1;
 
void SubtargetFeatureInfo::emitNameTable(
   // A small number of targets have no predicates. Null terminate the array to
   // avoid a zero-length array.
   OS << "  nullptr\n"
      << "};\n\n";
 }
 
 void SubtargetFeatureInfo::emitComputeAvailableFeatures(
     StringRef TargetName, StringRef ClassName, StringRef FuncName,
-    std::map<Record *, SubtargetFeatureInfo, LessRecordByID> &SubtargetFeatures,
-    raw_ostream &OS) {
+    SubtargetFeatureInfoMap &SubtargetFeatures, raw_ostream &OS,
+    StringRef ExtraParams) {
   OS << "PredicateBitset " << TargetName << ClassName << "::\n"
-     << FuncName << "(const MachineFunction *MF, const " << TargetName
-     << "Subtarget *Subtarget) const {\n";
+     << FuncName << "(const " << TargetName << "Subtarget *Subtarget";
+  if (!ExtraParams.empty())
+    OS << ", " << ExtraParams;
+  OS << ") const {\n";
   OS << "  PredicateBitset Features;\n";
   for (const auto &SF : SubtargetFeatures) {
     const SubtargetFeatureInfo &SFI = SF.second;
 
     OS << "  if (" << SFI.TheDef->getValueAsString("CondString") << ")\n";
     OS << "    Features[" << SFI.getEnumBitName() << "] = 1;\n";
   }
   OS << "  return Features;\n";
   OS << "}\n\n";
 }
 
 void SubtargetFeatureInfo::emitComputeAssemblerAvailableFeatures(
     StringRef TargetName, StringRef ClassName, StringRef FuncName,
-    std::map<Record *, SubtargetFeatureInfo, LessRecordByID> &SubtargetFeatures,
-    raw_ostream &OS) {
+    SubtargetFeatureInfoMap &SubtargetFeatures, raw_ostream &OS) {
   OS << "uint64_t " << TargetName << ClassName << "::\n"
      << FuncName << "(const FeatureBitset& FB) const {\n";
   OS << "  uint64_t Features = 0;\n";
   for (const auto &SF : SubtargetFeatures) {
     const SubtargetFeatureInfo &SFI = SF.second;
 
     OS << "  if (";
     std::string CondStorage =