[OperandBundles] Make function attributes conservatively correct

[sanjoy]

Summary

This makes attribute accessors on CallInst and InvokeInst do the
(conservatively) right thing. This essentially involves, in some
cases, *not* falling back querying the attributes on the called
llvm::Function when operand bundles are present.

Attributes locally present on the CallInst or InvokeInst will still
override operand bundle semantics. The LangRef has been amended to
reflect this. Note: this change does not do anything prevent
-function-attrs from inferring CallSite local attributes after
inspecting the called function -- that will be done as a separate
change.

I've used -adce and -early-cse to test these changes. There is
nothing special about these passes (and they did not require any
changes) except that they seemed be the easiest way to write the tests.

This change does not add deal with argmemonly. That's a later change
because alias analysis requires a related fix before argmemonly can be
tested.

[reames]

LGTM w/minor comments addressed

test/Feature/OperandBundles/adce.ll

5 ↗

(On Diff #38060)

Add a comment about *why* these need not be dead.

test/Feature/OperandBundles/early-cse.ll

5 ↗

(On Diff #38060)

Again, adding comments about what you're testing and why would be helpful.

llvm/trunk/docs/LangRef.rst

 - The bundle operands for an unknown operand bundle escape in unknown
   ways before control is transferred to the callee or invokee.
 - Calls and invokes with operand bundles have unknown read / write
   effect on the heap on entry and exit (even if the call target is
   ``readnone`` or ``readonly``).
 - An operand bundle at a call site cannot change the implementation
   of the called function.  Inter-procedural optimizations work as
   usual as long as they take into account the first two properties.
+- The bundle operands for an unknown operand bundle escape in unknown
+  ways before control is transferred to the callee or invokee.
+- Calls and invokes with operand bundles have unknown read / write
+  effect on the heap on entry and exit (even if the call target is
+  ``readnone`` or ``readonly``), unless they're overriden with
+  callsite specific attributes.
+- An operand bundle at a call site cannot change the implementation
+  of the called function.  Inter-procedural optimizations work as
+  usual as long as they take into account the first two properties.
 
 .. _moduleasm:
 
 Module-Level Inline Assembly
 ----------------------------
 
 Modules may contain "module-level inline asm" blocks, which corresponds
 to the GCC "file scope inline asm" blocks. These blocks are internally

llvm/trunk/include/llvm/IR/InstrTypes.h

 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_IR_INSTRTYPES_H
 #define LLVM_IR_INSTRTYPES_H
 
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/IR/Attributes.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/OperandTraits.h"
 
 namespace llvm {
 
 class LLVMContext;
 
for (unsigned i = 0, e = getNumOperandBundles(); i != e; ++i) {
       OperandBundleUse U = getOperandBundle(i);
       if (U.Tag == Name)
         return U;
     }
 
     return None;
   }
 
+  /// \brief Return true if this operand bundle user has operand bundles that
+  /// may read from the heap.
+  bool hasReadingOperandBundles() const {
+    // Implementation note: this is a conservative implementation of operand
+    // bundle semantics, where *any* operand bundle forces a callsite to be at
+    // least readonly.
+    return hasOperandBundles();
+  }
+
+  /// \brief Return true if this operand bundle user has operand bundles that
+  /// may write to the heap.
+  bool hasClobberingOperandBundles() const {
+    // Implementation note: this is a conservative implementation of operand
+    // bundle semantics, where *any* operand bundle forces a callsite to be
+    // read-write.
+    return hasOperandBundles();
+  }
 
 protected:
+  /// \brief Is the function attribute S disallowed by some operand bundle on
+  /// this operand bundle user?
+  bool isFnAttrDisallowedByOpBundle(StringRef S) const {
+    // Operand bundles only possibly disallow readnone and readonly attributes.
+    // All String attributes are fine.
+    return false;
+  }
+
+  /// \brief Is the function attribute A disallowed by some operand bundle on
+  /// this operand bundle user?
+  bool isFnAttrDisallowedByOpBundle(Attribute::AttrKind A) const {
+    switch (A) {
+    default:
+      return false;
+
+    case Attribute::ReadNone:
+      return hasReadingOperandBundles();
+
+    case Attribute::ReadOnly:
+      return hasClobberingOperandBundles();
+    }
+
+    llvm_unreachable("switch has a default case!");
+  }
+
   /// \brief Used to keep track of an operand bundle.  See the main comment on
   /// OperandBundleUser above.
   struct BundleOpInfo {
     /// \brief The operand bundle tag, interned by
     /// LLVMContextImpl::getOrInsertBundleTag.
     StringMapEntry<uint32_t> *Tag;
 
     /// \brief The index in the Use& vector where operands for this operand

llvm/trunk/include/llvm/IR/Instructions.h

public:
   static inline bool classof(const Value *V) {
     return isa<Instruction>(V) && classof(cast<Instruction>(V));
   }
 
 private:
   template <typename AttrKind> bool hasFnAttrImpl(AttrKind A) const {
     if (AttributeList.hasAttribute(AttributeSet::FunctionIndex, A))
       return true;
+
+    // Operand bundles override attributes on the called function, but don't
+    // override attributes directly present on the call instruction.
+    if (isFnAttrDisallowedByOpBundle(A))
+      return false;
+
     if (const Function *F = getCalledFunction())
       return F->getAttributes().hasAttribute(AttributeSet::FunctionIndex, A);
     return false;
   }
 
   // Shadow Instruction::setInstructionSubclassData with a private forwarding
   // method so that subclasses cannot accidentally use it.
   void setInstructionSubclassData(unsigned short D) {

llvm/trunk/lib/IR/Instructions.cpp

 }
 void InvokeInst::setSuccessorV(unsigned idx, BasicBlock *B) {
   return setSuccessor(idx, B);
 }
 
 bool InvokeInst::hasFnAttrImpl(Attribute::AttrKind A) const {
   if (AttributeList.hasAttribute(AttributeSet::FunctionIndex, A))
     return true;
+
+  // Operand bundles override attributes on the called function, but don't
+  // override attributes directly present on the invoke instruction.
+  if (isFnAttrDisallowedByOpBundle(A))
+    return false;
+
   if (const Function *F = getCalledFunction())
     return F->getAttributes().hasAttribute(AttributeSet::FunctionIndex, A);
   return false;
 }
 
 bool InvokeInst::paramHasAttr(unsigned i, Attribute::AttrKind A) const {
   if (AttributeList.hasAttribute(i, A))
     return true;

llvm/trunk/test/Feature/OperandBundles/adce.ll

+; RUN: opt -S -adce < %s | FileCheck %s
+
+; While it is normally okay to DCE out calls to @readonly_function and
+; @readnone_function, we cannot do that if they're carrying operand
+; bundles since the presence of unknown operand bundles implies
+; arbitrary memory effects.
+
+declare void @readonly_function() readonly nounwind
+declare void @readnone_function() readnone nounwind
+
+define void @test0() {
+; CHECK-LABEL: @test0(
+ entry:
+  call void @readonly_function() [ "tag"() ]
+; CHECK: call void @readonly_function
+  ret void
+}
+
+define void @test1() {
+; CHECK-LABEL: @test1(
+ entry:
+  call void @readnone_function() [ "tag"() ]
+; CHECK: call void @readnone_function
+  ret void
+}
+
+define void @test2() {
+; CHECK-LABEL: @test2(
+ entry:
+; CHECK-NOT: @readonly_function(
+  call void @readonly_function() readonly [ "tag"() ]
+  ret void
+}
+
+define void @test3() {
+; CHECK-LABEL: @test3(
+ entry:
+; CHECK-NOT: @readnone_function(
+  call void @readnone_function() readnone [ "tag"() ]
+  ret void
+}

llvm/trunk/test/Feature/OperandBundles/early-cse.ll

+; RUN: opt -S -early-cse < %s | FileCheck %s
+
+; While it is normally okay to do memory optimizations over calls to
+; @readonly_function and @readnone_function, we cannot do that if
+; they're carrying operand bundles since the presence of unknown
+; operand bundles implies arbitrary memory effects.
+
+declare void @readonly_function() readonly nounwind
+declare void @readnone_function() readnone nounwind
+
+define i32 @test0(i32* %x) {
+; CHECK-LABEL: @test0(
+ entry:
+  store i32 100, i32* %x
+; CHECK: store i32 100, i32* %x
+  call void @readonly_function() [ "tag"() ]
+; CHECK: call void @readonly_function()
+
+  %v = load i32, i32* %x
+; CHECK: %v = load i32, i32* %x
+; CHECK: ret i32 %v
+  ret i32 %v
+}
+
+define i32 @test1(i32* %x) {
+; CHECK: @test1(
+ entry:
+  store i32 100, i32* %x
+; CHECK: store i32 100, i32* %x
+  call void @readonly_function() readonly [ "tag"() ]
+; CHECK-NOT: call void @readonly_function
+  %v = load i32, i32* %x
+  ret i32 %v
+; CHECK: ret i32 100
+}
+
+define i32 @test3(i32* %x) {
+; CHECK-LABEL: @test3(
+ entry:
+  store i32 100, i32* %x
+; CHECK: store i32 100, i32* %x
+  call void @readonly_function()
+; CHECK-NOT: call void @readonly_function
+  %v = load i32, i32* %x
+  ret i32 %v
+; CHECK: ret i32 100
+}
+
+define void @test4(i32* %x) {
+; CHECK-LABEL: @test4(
+ entry:
+  store i32 100, i32* %x
+; CHECK: store i32 100, i32* %x
+  call void @readnone_function() [ "tag"() ]
+; CHECK: call void @readnone_function
+  store i32 200, i32* %x
+; CHECK: store i32 200, i32* %x
+  ret void
+}
+
+define void @test5(i32* %x) {
+; CHECK-LABEL: @test5(
+ entry:
+  store i32 100, i32* %x
+; CHECK-NOT: store i32 100, i32* %x
+; CHECK-NOT: call void @readnone_function
+  call void @readnone_function() readnone [ "tag"() ]
+  store i32 200, i32* %x
+; CHECK: store i32 200, i32* %x
+  ret void
+}