[Inline][Cloning] Drop incompatible attributes from NewFunc before instSimplify

Author: antoniofrighetto

llvm/lib/Transforms/Utils/CloneFunction.cpp

@@ -18,6 +18,7 @@
 #include "llvm/Analysis/DomTreeUpdater.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/IR/AttributeMask.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DebugInfo.h"
@@ -696,6 +697,16 @@ void llvm::CloneAndPruneIntoFromInst(Function *NewFunc, const Function *OldFunc,
     }
   }
 
+  // Drop all incompatible return attributes that cannot be applied to NewFunc
+  // during cloning, so as to allow instruction simplification later to reason
+  // on the old state of the function. The original attributes are restored
+  // before returning.
+  AttributeMask IncompatibleAttrs =
+      AttributeFuncs::typeIncompatible(OldFunc->getReturnType());
+  AttrBuilder RetAttrs(NewFunc->getContext(),
+                       NewFunc->getAttributes().getRetAttrs());
+  NewFunc->removeRetAttrs(IncompatibleAttrs);
+
   // Clone the entry block, and anything recursively reachable from it.
   std::vector<const BasicBlock *> CloneWorklist;
   PFC.CloneBlock(StartingBB, StartingInst->getIterator(), CloneWorklist);
@@ -849,6 +860,9 @@ void llvm::CloneAndPruneIntoFromInst(Function *NewFunc, const Function *OldFunc,
     }
   }
 
+  // Restore attributes.
+  NewFunc->addRetAttrs(RetAttrs);
+
   // Remap debug intrinsic operands now that all values have been mapped.
   // Doing this now (late) preserves use-before-defs in debug intrinsics. If
   // we didn't do this, ValueAsMetadata(use-before-def) operands would be

llvm/test/Transforms/Inline/inline-drop-attributes.ll

@@ -0,0 +1,32 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt < %s -passes=inline -S | FileCheck %s
+; RUN: opt < %s -passes='cgscc(inline)' -S | FileCheck %s
+
+define void @callee() {
+; CHECK-LABEL: define void @callee() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[VAL_PTR:%.*]] = load ptr, ptr null, align 8
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq ptr [[VAL_PTR]], null
+; CHECK-NEXT:    [[VAL:%.*]] = load i64, ptr null, align 8
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i64 undef, i64 [[VAL]]
+; CHECK-NEXT:    ret void
+;
+entry:
+  %val_ptr = load ptr, ptr null, align 8
+  %cmp = icmp eq ptr %val_ptr, null
+  %val = load i64, ptr null, align 8
+  %sel = select i1 %cmp, i64 undef, i64 %val
+  ret void
+}
+
+define noundef i1 @caller() {
+; CHECK-LABEL: define noundef i1 @caller() {
+; CHECK-NEXT:    [[VAL_PTR_I:%.*]] = load ptr, ptr null, align 8
+; CHECK-NEXT:    [[CMP_I:%.*]] = icmp eq ptr [[VAL_PTR_I]], null
+; CHECK-NEXT:    [[VAL_I:%.*]] = load i64, ptr null, align 8
+; CHECK-NEXT:    [[SEL_I:%.*]] = select i1 [[CMP_I]], i64 undef, i64 [[VAL_I]]
+; CHECK-NEXT:    ret i1 false
+;
+  call void @callee()
+  ret i1 false
+}