From ac6454a7f6cca0c8703b4f8c9eac125879d80409 Mon Sep 17 00:00:00 2001 From: Francis Visoiu Mistrih Date: Wed, 9 Jan 2019 19:46:15 +0000 Subject: [CodeGen] Ignore return sext/zext attributes of unused results for tail calls If the caller's return type does not have a zeroext attribute but the callee does a tail call zeroext, we won't consider the tail call during CodeGenPrepare because the attributes don't match. However, if the result of the tail call has no uses, it makes sense to drop the sext/zext attributes. Differential Revision: https://reviews.llvm.org/D56486 llvm-svn: 350753 --- llvm/lib/CodeGen/Analysis.cpp | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'llvm/lib/CodeGen/Analysis.cpp') diff --git a/llvm/lib/CodeGen/Analysis.cpp b/llvm/lib/CodeGen/Analysis.cpp index 27dce7fd7b7..797f05ee5cf 100644 --- a/llvm/lib/CodeGen/Analysis.cpp +++ b/llvm/lib/CodeGen/Analysis.cpp @@ -546,6 +546,21 @@ bool llvm::attributesPermitTailCall(const Function *F, const Instruction *I, 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. -- cgit v1.2.3