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[LICM][MustExec] Make must-exec logic for IV condition commutative #93150

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[LICM][MustExec] Make must-exec logic for IV condition commutative #93150

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17 changes: 11 additions & 6 deletions llvm/lib/Analysis/MustExecute.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -135,16 +135,21 @@ static bool CanProveNotTakenFirstIteration(const BasicBlock *ExitBlock,
// todo: this would be a lot more powerful if we used scev, but all the
// plumbing is currently missing to pass a pointer in from the pass
// Check for cmp (phi [x, preheader] ...), y where (pred x, y is known
ICmpInst::Predicate Pred = Cond->getPredicate();
auto *LHS = dyn_cast<PHINode>(Cond->getOperand(0));
auto *RHS = Cond->getOperand(1);
if (!LHS || LHS->getParent() != CurLoop->getHeader())
return false;
if (!LHS || LHS->getParent() != CurLoop->getHeader()) {
Pred = Cond->getSwappedPredicate();
LHS = dyn_cast<PHINode>(Cond->getOperand(1));
RHS = Cond->getOperand(0);
if (!LHS || LHS->getParent() != CurLoop->getHeader())
return false;
}

auto DL = ExitBlock->getModule()->getDataLayout();
auto *IVStart = LHS->getIncomingValueForBlock(CurLoop->getLoopPreheader());
auto *SimpleValOrNull = simplifyCmpInst(Cond->getPredicate(),
IVStart, RHS,
{DL, /*TLI*/ nullptr,
DT, /*AC*/ nullptr, BI});
auto *SimpleValOrNull = simplifyCmpInst(
Pred, IVStart, RHS, {DL, /*TLI*/ nullptr, DT, /*AC*/ nullptr, BI});
auto *SimpleCst = dyn_cast_or_null<Constant>(SimpleValOrNull);
if (!SimpleCst)
return false;
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3 changes: 1 addition & 2 deletions llvm/test/Transforms/LICM/hoist-mustexec.ll
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Expand Up @@ -218,7 +218,6 @@ fail:
}

; Same as previous case, with commuted icmp.
; FIXME: The load should get hoisted here as well.
define i32 @test3_commuted(ptr noalias nocapture readonly %a) nounwind uwtable {
; CHECK-LABEL: define i32 @test3_commuted(
; CHECK-SAME: ptr noalias nocapture readonly [[A:%.*]]) #[[ATTR1]] {
Expand All @@ -227,14 +226,14 @@ define i32 @test3_commuted(ptr noalias nocapture readonly %a) nounwind uwtable {
; CHECK-NEXT: [[IS_ZERO:%.*]] = icmp eq i32 [[LEN]], 0
; CHECK-NEXT: br i1 [[IS_ZERO]], label [[FAIL:%.*]], label [[PREHEADER:%.*]]
; CHECK: preheader:
; CHECK-NEXT: [[I1:%.*]] = load i32, ptr [[A]], align 4
; CHECK-NEXT: br label [[FOR_BODY:%.*]]
; CHECK: for.body:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 0, [[PREHEADER]] ], [ [[INC:%.*]], [[CONTINUE:%.*]] ]
; CHECK-NEXT: [[ACC:%.*]] = phi i32 [ 0, [[PREHEADER]] ], [ [[ADD:%.*]], [[CONTINUE]] ]
; CHECK-NEXT: [[R_CHK:%.*]] = icmp uge i32 [[LEN]], [[IV]]
; CHECK-NEXT: br i1 [[R_CHK]], label [[CONTINUE]], label [[FAIL_LOOPEXIT:%.*]]
; CHECK: continue:
; CHECK-NEXT: [[I1:%.*]] = load i32, ptr [[A]], align 4
; CHECK-NEXT: [[ADD]] = add nsw i32 [[I1]], [[ACC]]
; CHECK-NEXT: [[INC]] = add nuw nsw i32 [[IV]], 1
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp eq i32 [[INC]], 1000
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