From 611d645a08d154b46d9748bab73d5cc5180a6e68 Mon Sep 17 00:00:00 2001 From: Max Kazantsev Date: Wed, 22 Aug 2018 02:40:49 +0000 Subject: [PATCH] [GuardWidening] Ignore guards with trivial conditions Guard widening should not spend efforts on dealing with guards with trivial true/false conditions. Such guards can easily be eliminated by any further cleanup pass like instcombine. However we should not unconditionally delete them because it may be profitable to widen other conditions into such guards. Differential Revision: https://reviews.llvm.org/D50247 Reviewed By: fedor.sergeev llvm-svn: 340381 --- llvm/lib/Transforms/Scalar/GuardWidening.cpp | 6 ++++++ llvm/test/Transforms/GuardWidening/basic.ll | 26 ++++++++++++++++++++++++++ 2 files changed, 32 insertions(+) diff --git a/llvm/lib/Transforms/Scalar/GuardWidening.cpp b/llvm/lib/Transforms/Scalar/GuardWidening.cpp index 9467e5e..68be46e 100644 --- a/llvm/lib/Transforms/Scalar/GuardWidening.cpp +++ b/llvm/lib/Transforms/Scalar/GuardWidening.cpp @@ -347,6 +347,12 @@ bool GuardWideningImpl::eliminateGuardViaWidening( Instruction *GuardInst, const df_iterator &DFSI, const DenseMap> & GuardsInBlock, bool InvertCondition) { + // Ignore trivial true or false conditions. These instructions will be + // trivially eliminated by any cleanup pass. Do not erase them because other + // guards can possibly be widened into them. + if (isa(getCondition(GuardInst))) + return false; + Instruction *BestSoFar = nullptr; auto BestScoreSoFar = WS_IllegalOrNegative; auto *GuardInstLoop = LI.getLoopFor(GuardInst->getParent()); diff --git a/llvm/test/Transforms/GuardWidening/basic.ll b/llvm/test/Transforms/GuardWidening/basic.ll index 5b746a5..ab18ed7 100644 --- a/llvm/test/Transforms/GuardWidening/basic.ll +++ b/llvm/test/Transforms/GuardWidening/basic.ll @@ -379,3 +379,29 @@ left: right: ret void } + +; Make sure we do not widen guard by trivial true conditions into something. +define void @f_15(i1 %cond_0, i1 %cond_1) { +; CHECK-LABEL: @f_15( +entry: +; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %cond_0) [ "deopt"() ] +; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ] +; CHECK: ret void + + call void(i1, ...) @llvm.experimental.guard(i1 %cond_0) [ "deopt"() ] + call void(i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ] + ret void +} + +; Make sure we do not widen guard by trivial false conditions into something. +define void @f_16(i1 %cond_0, i1 %cond_1) { +; CHECK-LABEL: @f_16( +entry: +; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %cond_0) [ "deopt"() ] +; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 false) [ "deopt"() ] +; CHECK: ret void + + call void(i1, ...) @llvm.experimental.guard(i1 %cond_0) [ "deopt"() ] + call void(i1, ...) @llvm.experimental.guard(i1 false) [ "deopt"() ] + ret void +} -- 2.7.4