From 10aa7ea951e22dbd7f2ebdeb6410cfbc8a251eb1 Mon Sep 17 00:00:00 2001 From: Juneyoung Lee Date: Sun, 15 Mar 2020 01:34:33 +0900 Subject: [CodeGenPrepare] Freeze condition when transforming select to br Summary: This is a simple fix for CodeGenPrepare that freezes branch condition when transforming select to branch. If it is not freezed, instsimplify or the later pipeline can potentially exploit undefined behavior. The diff shows optimized form becase D75859 and D76048 already made a few changes to CodeGenPrepare for optimizing freeze(cmp). Reviewers: jdoerfert, spatel, lebedev.ri, efriedma Reviewed By: lebedev.ri Subscribers: hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D76179 --- llvm/lib/CodeGen/CodeGenPrepare.cpp | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) (limited to 'llvm/lib/CodeGen/CodeGenPrepare.cpp') diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp index 373064d..fd55ef2 100644 --- a/llvm/lib/CodeGen/CodeGenPrepare.cpp +++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp @@ -6131,7 +6131,8 @@ bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) { // Into: // start: // %cmp = cmp uge i32 %a, %b - // br i1 %cmp, label %select.true, label %select.false + // %cmp.frozen = freeze %cmp + // br i1 %cmp.frozen, label %select.true, label %select.false // select.true: // br label %select.end // select.false: @@ -6139,6 +6140,7 @@ bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) { // select.end: // %sel = phi i32 [ %c, %select.true ], [ %d, %select.false ] // + // %cmp should be freezed, otherwise it may introduce undefined behavior. // In addition, we may sink instructions that produce %c or %d from // the entry block into the destination(s) of the new branch. // If the true or false blocks do not contain a sunken instruction, that @@ -6217,7 +6219,9 @@ bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) { TT = TrueBlock; FT = FalseBlock; } - IRBuilder<>(SI).CreateCondBr(SI->getCondition(), TT, FT, SI); + IRBuilder<> IB(SI); + auto CondFr = IB.CreateFreeze(SI->getCondition(), SI->getName() + ".frozen"); + IB.CreateCondBr(CondFr, TT, FT, SI); SmallPtrSet INS; INS.insert(ASI.begin(), ASI.end()); -- cgit v1.1