[PATCH] D77977: [InstCombine] Simplify calls with casted "returned" attribute

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert created this revision.
jdoerfert added reviewers: nikic, spatel, lebedev.ri, nickdesaulniers.
Herald added subscribers: uenoku, bollu, hiraditya.
Herald added a reviewer: sstefan1.
Herald added a reviewer: uenoku.
Herald added a project: LLVM.

The handling of the `returned` attribute in D75815 <https://reviews.llvm.org/D75815> did miss the case
where the argument is (bit)casted to a different type. This is
explicitly allowed by the language reference and exposed by the
Attributor.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D77977

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
  llvm/test/Transforms/InstCombine/call-returned.ll


Index: llvm/test/Transforms/InstCombine/call-returned.ll
===================================================================
--- llvm/test/Transforms/InstCombine/call-returned.ll
+++ llvm/test/Transforms/InstCombine/call-returned.ll
@@ -3,6 +3,7 @@
 
 declare i32 @passthru_i32(i32 returned)
 declare i8* @passthru_p8(i8* returned)
+declare i8* @passthru_p8fromi32(i32* returned)
 
 define i32 @returned_const_int_arg() {
 ; CHECK-LABEL: @returned_const_int_arg(
@@ -22,6 +23,25 @@
   ret i8* %x
 }
 
+define i8* @returned_const_ptr_arg_casted() {
+; CHECK-LABEL: @returned_const_ptr_arg_casted(
+; CHECK-NEXT:    [[X:%.*]] = call i8* @passthru_p8fromi32(i32* null)
+; CHECK-NEXT:    ret i8* null
+;
+  %x = call i8* @passthru_p8fromi32(i32* null)
+  ret i8* %x
+}
+
+define i8* @returned_ptr_arg_casted(i32* %a) {
+; CHECK-LABEL: @returned_ptr_arg_casted(
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i32* [[A:%.*]] to i8*
+; CHECK-NEXT:    [[X:%.*]] = call i8* @passthru_p8fromi32(i32* [[A]])
+; CHECK-NEXT:    ret i8* [[TMP1]]
+;
+  %x = call i8* @passthru_p8fromi32(i32* %a)
+  ret i8* %x
+}
+
 define i32 @returned_var_arg(i32 %arg) {
 ; CHECK-LABEL: @returned_var_arg(
 ; CHECK-NEXT:    [[X:%.*]] = call i32 @passthru_i32(i32 [[ARG:%.*]])
@@ -48,3 +68,4 @@
   %x = musttail call i32 @passthru_i32(i32 %arg)
   ret i32 %x
 }
+
Index: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -4654,8 +4654,15 @@
   }
 
   if (!Call.use_empty() && !Call.isMustTailCall())
-    if (Value *ReturnedArg = Call.getReturnedArgOperand())
-      return replaceInstUsesWith(Call, ReturnedArg);
+    if (Value *ReturnedArg = Call.getReturnedArgOperand()) {
+      Type *CallTy = Call.getType();
+      Type *RetArgTy = ReturnedArg->getType();
+      if (RetArgTy == CallTy)
+        return replaceInstUsesWith(Call, ReturnedArg);
+      if (CallTy->isPointerTy() && RetArgTy->isPointerTy())
+        return replaceInstUsesWith(
+            Call, Builder.CreatePointerCast(ReturnedArg, CallTy));
+    }
 
   if (isAllocLikeFn(&Call, &TLI))
     return visitAllocSite(Call);


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