Index: lib/Transforms/Scalar/NewGVN.cpp =================================================================== --- lib/Transforms/Scalar/NewGVN.cpp +++ lib/Transforms/Scalar/NewGVN.cpp @@ -4094,10 +4094,13 @@ // It's about to be alive again. if (LeaderUseCount == 0 && isa(DominatingLeader)) ProbablyDead.erase(cast(DominatingLeader)); - // Copy instructions, however, are still dead because we use their - // operand as the leader. - if (LeaderUseCount == 0 && isSSACopy) - ProbablyDead.insert(II); + // For copy instructions, we use their operand as a leader, + // which means we remove a user of the copy and it may become dead. + if (isSSACopy) { + unsigned &IIUseCount = UseCounts[II]; + if (--IIUseCount == 0) + ProbablyDead.insert(II); + } ++LeaderUseCount; AnythingReplaced = true; } Index: test/Transforms/NewGVN/eliminate-ssacopy.ll =================================================================== --- /dev/null +++ test/Transforms/NewGVN/eliminate-ssacopy.ll @@ -0,0 +1,50 @@ +; RUN: opt -newgvn -S < %s | FileCheck %s + +; Make sure the created ssa copies are cleaned up. + +; CHECK-NOT: ssa_copy + +@b = external dso_local local_unnamed_addr global i32, align 4 +@a = external dso_local local_unnamed_addr global i8, align 1 +@f = external dso_local local_unnamed_addr global i16, align 2 + +define void @g() { +entry: + %tobool = icmp eq i32 undef, 0 + br i1 %tobool, label %for.cond1thread-pre-split, label %for.cond.preheader + +for.cond.preheader: ; preds = %entry + unreachable + +for.cond1thread-pre-split: ; preds = %entry + br label %for.end4.split + +for.end4.split: ; preds = %for.cond1thread-pre-split + br i1 %tobool, label %for.cond6.preheader, label %if.end11 + +for.cond6.preheader: ; preds = %for.end4.split + br i1 undef, label %for.cond6.preheader3, label %if.end11.loopexit + +for.cond6.preheader3: ; preds = %for.cond6.preheader + br label %if.end11.loopexit + +if.end11.loopexit: ; preds = %for.cond6.preheader3, %for.cond6.preheader + %storemerge.lcssa = phi i32 [ 0, %for.cond6.preheader ], [ 1, %for.cond6.preheader3 ] + store i32 %storemerge.lcssa, i32* @b, align 4 + br label %if.end11 + +if.end11: ; preds = %if.end11.loopexit, %for.end4.split + %0 = load i32, i32* @b, align 4 + %1 = load i8, i8* @a, align 1 + %conv = sext i8 %1 to i32 + %cmp12 = icmp eq i32 %0, %conv + br i1 %cmp12, label %if.then14, label %if.end16 + +if.then14: ; preds = %if.end11 + %conv15 = trunc i32 %0 to i16 + store i16 %conv15, i16* @f, align 2 + unreachable + +if.end16: ; preds = %if.end11 + ret void +}