[PATCH] D75824: [InstSimplify] Don't simplify musttail calls

[Nikita Popov via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG829d377a98fd: [InstSimplify] Don't simplify musttail calls (authored by nikic).
Herald added a subscriber: hiraditya.

Changed prior to commit:
  https://reviews.llvm.org/D75824?vs=248994&id=249162#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D75824/new/

https://reviews.llvm.org/D75824

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/test/Transforms/InstSimplify/call.ll


Index: llvm/test/Transforms/InstSimplify/call.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/call.ll
+++ llvm/test/Transforms/InstSimplify/call.ll
@@ -1007,3 +1007,30 @@
   %x = call i32 @passthru_i32(i32 %arg)
   ret i32 %x
 }
+
+define i32 @returned_const_int_arg_musttail(i32 %arg) {
+; CHECK-LABEL: @returned_const_int_arg_musttail(
+; CHECK-NEXT:    [[X:%.*]] = musttail call i32 @passthru_i32(i32 42)
+; CHECK-NEXT:    ret i32 [[X]]
+;
+  %x = musttail call i32 @passthru_i32(i32 42)
+  ret i32 %x
+}
+
+define i32 @returned_var_arg_musttail(i32 %arg) {
+; CHECK-LABEL: @returned_var_arg_musttail(
+; CHECK-NEXT:    [[X:%.*]] = musttail call i32 @passthru_i32(i32 [[ARG:%.*]])
+; CHECK-NEXT:    ret i32 [[X]]
+;
+  %x = musttail call i32 @passthru_i32(i32 %arg)
+  ret i32 %x
+}
+
+define i32 @call_undef_musttail() {
+; CHECK-LABEL: @call_undef_musttail(
+; CHECK-NEXT:    [[X:%.*]] = musttail call i32 undef()
+; CHECK-NEXT:    ret i32 [[X]]
+;
+  %x = musttail call i32 undef()
+  ret i32 %x
+}
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5330,6 +5330,11 @@
 Value *llvm::SimplifyCall(CallBase *Call, const SimplifyQuery &Q) {
   Value *Callee = Call->getCalledValue();
 
+  // musttail calls can only be simplified if they are also DCEd.
+  // As we can't guarantee this here, don't simplify them.
+  if (Call->isMustTailCall())
+    return nullptr;
+
   // call undef -> undef
   // call null -> undef
   if (isa<UndefValue>(Callee) || isa<ConstantPointerNull>(Callee))
@@ -5512,6 +5517,9 @@
     break;
   case Instruction::Call: {
     Result = SimplifyCall(cast<CallInst>(I), Q);
+    // Don't perform known bits simplification below for musttail calls.
+    if (cast<CallInst>(I)->isMustTailCall())
+      return Result;
     break;
   }
   case Instruction::Freeze:


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