[PATCH] D56486: [CodeGen] Ignore return sext/zext attributes of unused results for tail calls

[Francis Visoiu Mistrih via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL350753: [CodeGen] Ignore return sext/zext attributes of unused results for tail calls (authored by thegameg, committed by ).

Changed prior to commit:
  https://reviews.llvm.org/D56486?vs=180815&id=180895#toc

Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D56486/new/

https://reviews.llvm.org/D56486

Files:
  llvm/trunk/lib/CodeGen/Analysis.cpp
  llvm/trunk/test/CodeGen/AArch64/tail-call-unused-zext.ll


Index: llvm/trunk/test/CodeGen/AArch64/tail-call-unused-zext.ll
===================================================================
--- llvm/trunk/test/CodeGen/AArch64/tail-call-unused-zext.ll
+++ llvm/trunk/test/CodeGen/AArch64/tail-call-unused-zext.ll
@@ -0,0 +1,36 @@
+; RUN: llc -mtriple=arm64--- -stop-after=expand-isel-pseudos -o - %s | FileCheck %s
+
+; Check that we ignore the zeroext attribute on the return type of the tail
+; call, since the return value is unused. This happens during CodeGenPrepare in
+; dupRetToEnableTailCallOpts, which calls attributesPermitTailCall to check if
+; the attributes of the caller and the callee match.
+
+declare zeroext i1 @zcallee()
+define void @zcaller() {
+; CHECK-LABEL: name: zcaller
+entry:
+  br i1 undef, label %calllabel, label %retlabel
+calllabel:
+; CHECK: bb.1.calllabel:
+; CHECK-NOT: BL @zcallee
+; CHECK-NEXT: TCRETURNdi @zcallee
+  %unused_result = tail call zeroext i1 @zcallee()
+  br label %retlabel
+retlabel:
+  ret void
+}
+
+declare signext i1 @scallee()
+define void @scaller() {
+; CHECK-LABEL: name: scaller
+entry:
+  br i1 undef, label %calllabel, label %retlabel
+calllabel:
+; CHECK: bb.1.calllabel:
+; CHECK-NOT: BL @scallee
+; CHECK-NEXT: TCRETURNdi @scallee
+  %unused_result = tail call signext i1 @scallee()
+  br label %retlabel
+retlabel:
+  ret void
+}
Index: llvm/trunk/lib/CodeGen/Analysis.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/Analysis.cpp
+++ llvm/trunk/lib/CodeGen/Analysis.cpp
@@ -546,6 +546,21 @@
     CalleeAttrs.removeAttribute(Attribute::SExt);
   }
 
+  // Drop sext and zext return attributes if the result is not used.
+  // This enables tail calls for code like:
+  //
+  // define void @caller() {
+  // entry:
+  //   %unused_result = tail call zeroext i1 @callee()
+  //   br label %retlabel
+  // retlabel:
+  //   ret void
+  // }
+  if (I->use_empty()) {
+    CalleeAttrs.removeAttribute(Attribute::SExt);
+    CalleeAttrs.removeAttribute(Attribute::ZExt);
+  }
+
   // If they're still different, there's some facet we don't understand
   // (currently only "inreg", but in future who knows). It may be OK but the
   // only safe option is to reject the tail call.


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