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GVN: tolerate an instruction being replaced without existing in the leaderboard 

Sometimes an incidentally created instruction can duplicate a Value used
elsewhere. It then often doesn't end up in the leader table. If it's later
removed, we attempt to remove it from the leader table and segfault.

Instead we should just ignore the removal request, which won't cause any
problems. The reverse situation, where the original instruction is replaced by
the new one (which you might think could leave the leader table empty) cannot
occur, because the incidental instruction will never be found in the first
place.

llvm-svn: 242199
This commit is contained in:
Tim Northover 2015-07-14 21:03:18 +00:00
parent d30e2eefc3
commit d5fdef016d
2 changed files with 33 additions and 1 deletions
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5
llvm/lib/Transforms/Scalar/GVN.cpp
View File

@ -656,11 +656,14 @@ namespace {
LeaderTableEntry* Prev = nullptr;
LeaderTableEntry* Curr = &LeaderTable[N];
while (Curr->Val != I || Curr->BB != BB) {
while (Curr && (Curr->Val != I || Curr->BB != BB)) {
Prev = Curr;
Curr = Curr->Next;
}
if (!Curr)
return;
if (Prev) {
Prev->Next = Curr->Next;
} else {

29
llvm/test/Transforms/GVN/pre-new-inst.ll Normal file
View File

@ -0,0 +1,29 @@
; RUN: opt -basicaa -gvn -S %s | FileCheck %s
%MyStruct = type { i32, i32 }
define i8 @foo(i64 %in, i8* %arr) {
%addr = alloca %MyStruct
%dead = trunc i64 %in to i32
br i1 undef, label %next, label %tmp
tmp:
call void @bar()
br label %next
next:
%addr64 = bitcast %MyStruct* %addr to i64*
store i64 %in, i64* %addr64
br label %final
final:
%addr32 = getelementptr %MyStruct, %MyStruct* %addr, i32 0, i32 0
%idx32 = load i32, i32* %addr32
; CHECK: %resptr = getelementptr i8, i8* %arr, i32 %dead
%resptr = getelementptr i8, i8* %arr, i32 %idx32
%res = load i8, i8* %resptr
ret i8 %res
}
declare void @bar()