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[IndVarSimplify] Don't replace IV user with unsafe loop-invariant (PR45360)

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Summary:
As [[ https://bugs.llvm.org/show_bug.cgi?id=45360 | PR45360 ]] reports,
with new cost-model we can sometimes end up being able to expand `udiv`/`urem` instructions.
And that exposes at least one instance of when we do that
regardless of whether or not it is safe to do.
In this particular case, it's `SimplifyIndvar::replaceIVUserWithLoopInvariant()`.

It seems to me, we simply need to check with `isSafeToExpandAt()` first.

The test isn't great. I'm not sure how to make it only run `-indvars`.

Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=45360 | PR45360 ]].

Reviewers: mkazantsev, reames, helloqirun

Reviewed By: mkazantsev

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D82108
This commit is contained in:
Roman Lebedev 2020-06-23 13:52:21 +03:00
parent 4cc65c325c
commit a84c0f066c
2 changed files with 11 additions and 4 deletions
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9
lib/Transforms/Utils/SimplifyIndVar.cpp
View File

@ -657,7 +657,7 @@ static Instruction *GetLoopInvariantInsertPosition(Loop *L, Instruction *Hint) {
return Hint;
}
/// Replace the UseInst with a constant if possible.
/// Replace the UseInst with a loop invariant expression if it is safe.
bool SimplifyIndvar::replaceIVUserWithLoopInvariant(Instruction *I) {
if (!SE->isSCEVable(I->getType()))
return false;
@ -673,6 +673,13 @@ bool SimplifyIndvar::replaceIVUserWithLoopInvariant(Instruction *I) {
return false;
auto *IP = GetLoopInvariantInsertPosition(L, I);
if (!isSafeToExpandAt(S, IP, *SE)) {
LLVM_DEBUG(dbgs() << "INDVARS: Can not replace IV user: " << *I
<< " with non-speculable loop invariant: " << *S << '\n');
return false;
}
auto *Invariant = Rewriter.expandCodeFor(S, I->getType(), IP);
I->replaceAllUsesWith(Invariant);

6
test/Transforms/IndVarSimplify/X86/pr45360.ll
View File

@ -26,7 +26,6 @@ define dso_local i32 @main() {
; CHECK: bb19:
; CHECK-NEXT: [[I8_LCSSA9:%.*]] = phi i32 [ [[D_PROMOTED8]], [[BB:%.*]] ], [ [[I8:%.*]], [[BB27:%.*]] ]
; CHECK-NEXT: [[I8]] = and i32 [[I8_LCSSA9]], [[I6]]
; CHECK-NEXT: [[TMP0:%.*]] = urem i32 [[I24]], [[I8]]
; CHECK-NEXT: [[I21:%.*]] = icmp eq i32 [[I8]], 0
; CHECK-NEXT: br i1 [[I21]], label [[BB27_THREAD:%.*]], label [[BB27]]
; CHECK: bb27.thread:
@ -35,8 +34,9 @@ define dso_local i32 @main() {
; CHECK-NEXT: store i32 0, i32* @c, align 4
; CHECK-NEXT: br label [[BB32:%.*]]
; CHECK: bb27:
; CHECK-NEXT: store i32 [[TMP0]], i32* @e, align 4
; CHECK-NEXT: [[I30:%.*]] = icmp eq i32 [[TMP0]], 0
; CHECK-NEXT: [[I26:%.*]] = urem i32 [[I24]], [[I8]]
; CHECK-NEXT: store i32 [[I26]], i32* @e, align 4
; CHECK-NEXT: [[I30:%.*]] = icmp eq i32 [[I26]], 0
; CHECK-NEXT: br i1 [[I30]], label [[BB32_LOOPEXIT:%.*]], label [[BB19]]
; CHECK: bb32.loopexit:
; CHECK-NEXT: store i32 -1, i32* @f, align 4