AArch64 : Implement GHC calling convention.

[erikd]

Summary

Original patch authored by Luke Iannini. Minor improvements and test
added by Erik de Castro Lopo.

[erikd]

This patch was previously discussed here: http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20141103/243180.html .

WIth this patch applied to llvm-3.5 I can cross-compile simple haskell programs (haven't tried anything complicated) from x86_64-linux to aarch64-linux and generate binaries that execute correctly.

I can't use llvm-3.6 or git HEAD because the current GHC LLVM backend doesn't support those versions yet. When GHC is updated it is extremely unlikely that any changes would be required for this AArch64 GHC calling convention code.

If possible, I'd like to see this patch land in the llvm 3.6 release.

[erikd]

Fix author email address.

[garious]

Erik, thanks for doing this work. I'd love to see GHC AArch64 support make it into 3.6. I'd be more comfortable with this patch if there was a bit more information about the .td file changes and if the test had coverage similar to the X86_64 one (see: test/CodeGen/X86/ghc-cc64.ll).

lib/Target/AArch64/AArch64CallingConvention.td

208

Is there a document you can reference here?

213

I'm having trouble groking this. It looks like a combination of the X86 GHC version and CC_AArch64_AAPCS (perhaps an old version?). I wonder, is it possible to inherit from CC_AArch64_AAPCS and tweak the derived version for GHC?

test/CodeGen/AArch64/ghc-tcreturn-lowered.ll

14

Does this case add coverage? Compared to the one above, seems like it would only affect the bitcode just before the tail call.

[erikd]

• Added comments documenting the GHC calling convention with references to GHC Wiki and the GHC source code.
• Significant improvements to the ghccc tests (borrowing heavily from the x86-64 ghccc test).

[garious]

Thanks Erik. Good test and looks consistent with the X86_64 implementation. I'll try to find one more person to review. Hopefully we can land this one soon.

[erikd]

Ping? I know its only been up a week or so, but I was hoping to get this into the 3.6 release.

The chances of this commit breaking anything other the the GHC calling convention on AArch64 is rather small and without this patch, the GHC calling convention for AArch64 doesn't work at all.

[rengolin]

Hi Erik,

The changes look harmless to me, but I'd like to see slightly better tests before this goes in.

cheers,
--renato

test/CodeGen/AArch64/ghc-cc.ll

28 ↗

(On Diff #18071)

If you're checking for the absence of prologue, I'd recommend you used CHECK-NOT, instead of CHECK-NEXT with some instruction, because:

1. It tells us what the test is about, and
2. It's less fragile to codegen changes.

46 ↗

(On Diff #18071)

The more CHECK-NEXT you use, the more fragile the test will be to codegen changes. Though, in these cases, CHECK-DAG will not be as efficient/correct.

Maybe what you should do, since there are no prologues and no stack (I'm assuming), you should create multiple functions, one for each type of parameter, and test it with CHECK-NEXT in an atomic way (for each example, a pair of CHECK + CHECK-NEXT *after* the CHECK-LABEL).

[erikd]

• Simplify tests to reduce chance of false failure.

[rengolin]

Apart from the typo, LGTM. Please, commit with the change.

cheers,
--renato

test/CodeGen/AArch64/ghc-cc.ll

38 ↗

(On Diff #18373)

typo :)

[erikd]

• Fix typoes.

[rengolin]

test/CodeGen/AArch64/ghc-cc.ll

37 ↗

(On Diff #18375)

Would be good to have a CHECK-LABEL here, too.

[garious]

Committed in r226473. Renato, I added the CHECK-LABEL you mentioned.

Thanks Erik!

[rengolin]

Thanks!

lib/Target/AArch64/AArch64CallingConvention.td

def RetCC_AArch64_WebKit_JS : CallingConv<[
   CCIfType<[i64], CCAssignToRegWithShadow<[X0, X1, X2, X3, X4, X5, X6, X7],
                                           [W0, W1, W2, W3, W4, W5, W6, W7]>>,
   CCIfType<[f32], CCAssignToRegWithShadow<[S0, S1, S2, S3, S4, S5, S6, S7],
                                           [Q0, Q1, Q2, Q3, Q4, Q5, Q6, Q7]>>,
   CCIfType<[f64], CCAssignToRegWithShadow<[D0, D1, D2, D3, D4, D5, D6, D7],
                                           [Q0, Q1, Q2, Q3, Q4, Q5, Q6, Q7]>>
 ]>;
 
+//===----------------------------------------------------------------------===//
+// ARM64 Calling Convention for GHC
+//===----------------------------------------------------------------------===//
+
+def CC_AArch64_GHC : CallingConv<[
+  // Handle all vector types as either f64 or v2f64.
+  CCIfType<[v1i64, v2i32, v4i16, v8i8, v2f32], CCBitConvertToType<f64>>,
+  CCIfType<[v2i64, v4i32, v8i16, v16i8, v4f32, f128], CCBitConvertToType<v2f64>>,
+
+  CCIfType<[v2f64], CCAssignToReg<[Q4, Q5]>>,
+  CCIfType<[f32], CCAssignToReg<[S8, S9, S10, S11]>>,
+  CCIfType<[f64], CCAssignToReg<[D12, D13, D14, D15]>>,
+
+  // Promote i8/i16/i32 arguments to i64.
+  CCIfType<[i8, i16, i32], CCPromoteToType<i64>>,
+
+  // Pass in STG registers: Base, Sp, Hp, R1, R2, R3, R4, R5, R6, SpLim
+  CCIfType<[i64], CCAssignToReg<[X19, X20, X21, X22, X23, X24, X25, X26, X27, X28]>>
+]>;
+
 // FIXME: LR is only callee-saved in the sense that *we* preserve it and are
 // presumably a callee to someone. External functions may not do so, but this
 // is currently safe since BL has LR as an implicit-def and what happens after a
 // tail call doesn't matter.
 //
 // It would be better to model its preservation semantics properly (create a
 // vreg on entry, use it in RET & tail call generation; make that vreg def if we
 // end up saving LR as part of a call frame). Watch this space...

 
 def CSR_AArch64_AllRegs
     : CalleeSavedRegs<(add (sequence "W%u", 0, 30), WSP,
                            (sequence "X%u", 0, 28), FP, LR, SP,
                            (sequence "B%u", 0, 31), (sequence "H%u", 0, 31),
                            (sequence "S%u", 0, 31), (sequence "D%u", 0, 31),
                            (sequence "Q%u", 0, 31))>;
 
+def CSR_AArch64_NoRegs : CalleeSavedRegs<(add)>;
 No newline at end of file

lib/Target/AArch64/AArch64FastISel.cpp

static unsigned getImplicitScaleFactor(MVT VT) {
   case MVT::f64:
     return 8;
   }
 }
 
 CCAssignFn *AArch64FastISel::CCAssignFnForCall(CallingConv::ID CC) const {
   if (CC == CallingConv::WebKit_JS)
     return CC_AArch64_WebKit_JS;
+  if (CC == CallingConv::GHC)
+    return CC_AArch64_GHC;
   return Subtarget->isTargetDarwin() ? CC_AArch64_DarwinPCS : CC_AArch64_AAPCS;
 }
 
 unsigned AArch64FastISel::fastMaterializeAlloca(const AllocaInst *AI) {
   assert(TLI.getValueType(AI->getType(), true) == MVT::i64 &&
          "Alloca should always return a pointer.");
 
   // Don't handle dynamic allocas.

lib/Target/AArch64/AArch64FrameLowering.cpp

const AArch64RegisterInfo *RegInfo = static_cast<const AArch64RegisterInfo *>(
       MF.getSubtarget().getRegisterInfo());
   const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
   MachineModuleInfo &MMI = MF.getMMI();
   AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
   bool needsFrameMoves = MMI.hasDebugInfo() || Fn->needsUnwindTableEntry();
   bool HasFP = hasFP(MF);
   DebugLoc DL = MBB.findDebugLoc(MBBI);
 
+  // All calls are tail calls in GHC calling conv, and functions have no
+  // prologue/epilogue.
+  if (MF.getFunction()->getCallingConv() == CallingConv::GHC)
+    return;
+
   int NumBytes = (int)MFI->getStackSize();
   if (!AFI->hasStackFrame()) {
     assert(!HasFP && "unexpected function without stack frame but with FP");
 
     // All of the stack allocation is for locals.
     AFI->setLocalStackSize(NumBytes);
 
     // Label used to tie together the PROLOG_LABEL and the MachineMoves.
void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
   const AArch64RegisterInfo *RegInfo = static_cast<const AArch64RegisterInfo *>(
       MF.getSubtarget().getRegisterInfo());
   DebugLoc DL = MBBI->getDebugLoc();
   unsigned RetOpcode = MBBI->getOpcode();
 
   int NumBytes = MFI->getStackSize();
   const AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
 
+  // All calls are tail calls in GHC calling conv, and functions have no
+  // prologue/epilogue.
+  if (MF.getFunction()->getCallingConv() == CallingConv::GHC)
+    return;
+
   // Initial and residual are named for consitency with the prologue. Note that
   // in the epilogue, the residual adjustment is executed first.
   uint64_t ArgumentPopSize = 0;
   if (RetOpcode == AArch64::TCRETURNdi || RetOpcode == AArch64::TCRETURNri) {
     MachineOperand &StackAdjust = MBBI->getOperand(1);
 
     // For a tail-call in a callee-pops-arguments environment, some or all of
     // the stack may actually be in use for the call's arguments, this is

lib/Target/AArch64/AArch64ISelLowering.cpp

 /// Selects the correct CCAssignFn for a given CallingConvention value.
 CCAssignFn *AArch64TargetLowering::CCAssignFnForCall(CallingConv::ID CC,
                                                      bool IsVarArg) const {
   switch (CC) {
   default:
     llvm_unreachable("Unsupported calling convention.");
   case CallingConv::WebKit_JS:
     return CC_AArch64_WebKit_JS;
+  case CallingConv::GHC:
+    return CC_AArch64_GHC;
   case CallingConv::C:
   case CallingConv::Fast:
     if (!Subtarget->isTargetDarwin())
       return CC_AArch64_AAPCS;
     return IsVarArg ? CC_AArch64_DarwinPCS_VarArg : CC_AArch64_DarwinPCS;
   }
 }
 

lib/Target/AArch64/AArch64RegisterInfo.cpp

 
 AArch64RegisterInfo::AArch64RegisterInfo(const AArch64InstrInfo *tii,
                                          const AArch64Subtarget *sti)
     : AArch64GenRegisterInfo(AArch64::LR), TII(tii), STI(sti) {}
 
 const MCPhysReg *
 AArch64RegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
   assert(MF && "Invalid MachineFunction pointer.");
+  if (MF->getFunction()->getCallingConv() == CallingConv::GHC)
+    // GHC set of callee saved regs is empty as all those regs are
+    // used for passing STG regs around
+    return CSR_AArch64_NoRegs_SaveList;
   if (MF->getFunction()->getCallingConv() == CallingConv::AnyReg)
     return CSR_AArch64_AllRegs_SaveList;
   else
     return CSR_AArch64_AAPCS_SaveList;
 }
 
 const uint32_t *
 AArch64RegisterInfo::getCallPreservedMask(CallingConv::ID CC) const {
+  if (CC == CallingConv::GHC)
+    // This is academic becase all GHC calls are (supposed to be) tail calls
+    return CSR_AArch64_NoRegs_RegMask;
   if (CC == CallingConv::AnyReg)
     return CSR_AArch64_AllRegs_RegMask;
   else
     return CSR_AArch64_AAPCS_RegMask;
 }
 
 const uint32_t *AArch64RegisterInfo::getTLSCallPreservedMask() const {
   if (STI->isTargetDarwin())
     return CSR_AArch64_TLS_Darwin_RegMask;
 
   assert(STI->isTargetELF() && "only expect Darwin or ELF TLS");
   return CSR_AArch64_TLS_ELF_RegMask;
 }
 
 const uint32_t *
-AArch64RegisterInfo::getThisReturnPreservedMask(CallingConv::ID) const {
+AArch64RegisterInfo::getThisReturnPreservedMask(CallingConv::ID CC) const {
   // This should return a register mask that is the same as that returned by
   // getCallPreservedMask but that additionally preserves the register used for
   // the first i64 argument (which must also be the register used to return a
   // single i64 return value)
   //
   // In case that the calling convention does not use the same register for
   // both, the function should return NULL (does not currently apply)
+  assert(CC != CallingConv::GHC && "should not be GHC calling convention.");
   return CSR_AArch64_AAPCS_ThisReturn_RegMask;
 }
 
 BitVector
 AArch64RegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
 
   // FIXME: avoid re-calculating this every time.

test/CodeGen/AArch64/ghc-tcreturn-lowered.ll

+; RUN: llc -mtriple=aarch64-unknown-linux-gnu -o - %s | FileCheck %s
+
+declare cc10 void @gfunc()
+
+define cc10 void @test_direct_tail() {
+; CHECK-LABEL: test_direct_tail:
+; CHECK: bl gfunc
+  tail call cc10 void @gfunc()
+  ret void
+}
+
+@ind_func = global void()* zeroinitializer
+
+define cc10 void @test_indirect_tail() {
+; CHECK-LABEL: test_indirect_tail:
+; CHECK: adrp {{x[0-9]+}}, ind_func
+; CHECK-NEXT: ldr {{x[0-9]+}}, [{{x[0-9]+}}, :lo12:ind_func]
+; CHECK-NEXT: blr {{x[0-9]+}}
+  %func = load void()** @ind_func
+  tail call cc10 void()* %func()
+  ret void
+}