[PATCH] D56486: [CodeGen] Ignore return sext/zext attributes of unused results for tail calls
Francis Visoiu Mistrih via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Wed Jan 9 11:51:43 PST 2019
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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