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[ConstraintElim] Support decrementing inductions with step -1. #68644

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Merged
merged 2 commits into from
Oct 10, 2023
Merged

[ConstraintElim] Support decrementing inductions with step -1. #68644

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a737357
[ConstraintElim] Support decrementing inductions with step -1.
fhahn Aug 23, 2023
331ceb3
Remove stray character
fhahn Oct 10, 2023
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20 changes: 20 additions & 0 deletions llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -889,6 +889,26 @@ void State::addInfoForInductions(BasicBlock &BB) {
else
return;

// Handle negative steps.
if (StepOffset.isNegative()) {
// TODO: Extend to allow steps > -1.
if (!(-StepOffset).isOne())
return;

// AR may wrap.
// Add StartValue >= PN conditional on B <= StartValue which guarantees that
// the loop exits before wrapping with a step of -1.
WorkList.push_back(FactOrCheck::getConditionFact(
DTN, CmpInst::ICMP_UGE, StartValue, PN,
ConditionTy(CmpInst::ICMP_ULE, B, StartValue)));
// Add PN > B conditional on B <= StartValue which guarantees that the loop
// exits when reaching B with a step of -1.
WorkList.push_back(FactOrCheck::getConditionFact(
DTN, CmpInst::ICMP_UGT, PN, B,
ConditionTy(CmpInst::ICMP_ULE, B, StartValue)));
return;
}

// Make sure AR either steps by 1 or that the value we compare against is a
// GEP based on the same start value and all offsets are a multiple of the
// step size, to guarantee that the induction will reach the value.
Expand Down
6 changes: 2 additions & 4 deletions llvm/test/Transforms/ConstraintElimination/monotonic-int-phis-decrement.ll
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Expand Up @@ -14,8 +14,7 @@ define void @add_rec_decreasing_cond_true_constant(i8 noundef %len) {
; CHECK-NEXT: [[CMP2_NOT:%.*]] = icmp eq i8 [[K_0]], 0
; CHECK-NEXT: br i1 [[CMP2_NOT]], label [[EXIT:%.*]], label [[LOOP_LATCH]]
; CHECK: loop.latch:
; CHECK-NEXT: [[CMP_NOT_I:%.*]] = icmp ult i8 [[K_0]], 5
; CHECK-NEXT: call void @use(i1 [[CMP_NOT_I]])
; CHECK-NEXT: call void @use(i1 true)
; CHECK-NEXT: [[K_DEC]] = add i8 [[K_0]], -1
; CHECK-NEXT: br label [[LOOP_HEADER]]
; CHECK: exit:
Expand Down Expand Up @@ -87,8 +86,7 @@ define void @add_rec_decreasing_cond_true_start_signed_positive(i8 noundef %star
; CHECK-NEXT: [[CMP2_NOT:%.*]] = icmp eq i8 [[K_0]], 0
; CHECK-NEXT: br i1 [[CMP2_NOT]], label [[EXIT:%.*]], label [[LOOP_LATCH]]
; CHECK: loop.latch:
; CHECK-NEXT: [[CMP_NOT_I:%.*]] = icmp ult i8 [[K_0]], [[START]]
; CHECK-NEXT: call void @use(i1 [[CMP_NOT_I]])
; CHECK-NEXT: call void @use(i1 true)
; CHECK-NEXT: [[K_DEC]] = add i8 [[K_0]], -1
; CHECK-NEXT: br label [[LOOP_HEADER]]
; CHECK: exit:
Expand Down
3 changes: 1 addition & 2 deletions llvm/test/Transforms/ConstraintElimination/monotonic-int-phis-nested-loops.ll
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Expand Up @@ -117,8 +117,7 @@ define void @inner_add_rec_decreasing(i32 noundef %len) {
; CHECK-NEXT: [[CMP2_NOT:%.*]] = icmp eq i32 [[K_0]], 0
; CHECK-NEXT: br i1 [[CMP2_NOT]], label [[OUTER_LATCH]], label [[INNER_LATCH]]
; CHECK: inner.latch:
; CHECK-NEXT: [[CMP_NOT_I:%.*]] = icmp ult i32 [[K_0]], [[LEN]]
; CHECK-NEXT: call void @use(i1 [[CMP_NOT_I]])
; CHECK-NEXT: call void @use(i1 true)
; CHECK-NEXT: [[K_DEC]] = add i32 [[K_0]], -1
; CHECK-NEXT: br label [[INNER_HEADER]]
; CHECK: outer.latch:
Expand Down
10 changes: 2 additions & 8 deletions llvm/test/Transforms/PhaseOrdering/loop-access-checks.ll
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Expand Up @@ -270,7 +270,7 @@ declare void @abort()

define void @monkey(ptr noundef %arr, i32 noundef %len) {
; CHECK-LABEL: define void @monkey
; CHECK-SAME: (ptr nocapture noundef [[ARR:%.*]], i32 noundef [[LEN:%.*]]) local_unnamed_addr {
; CHECK-SAME: (ptr nocapture noundef [[ARR:%.*]], i32 noundef [[LEN:%.*]]) local_unnamed_addr #[[ATTR1:[0-9]+]] {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP8:%.*]] = icmp ugt i32 [[LEN]], 1
; CHECK-NEXT: br i1 [[CMP8]], label [[FOR_BODY4_PREHEADER:%.*]], label [[FOR_COND_CLEANUP:%.*]]
Expand All @@ -284,13 +284,7 @@ define void @monkey(ptr noundef %arr, i32 noundef %len) {
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[INC]], [[LEN]]
; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY4_PREHEADER]], label [[FOR_COND_CLEANUP]]
; CHECK: for.body4:
; CHECK-NEXT: [[K_07:%.*]] = phi i32 [ [[DEC:%.*]], [[AT_EXIT:%.*]] ], [ [[I_09]], [[FOR_BODY4_PREHEADER]] ]
; CHECK-NEXT: [[CMP_NOT_I:%.*]] = icmp ult i32 [[K_07]], [[LEN]]
; CHECK-NEXT: br i1 [[CMP_NOT_I]], label [[AT_EXIT]], label [[IF_THEN_I:%.*]]
; CHECK: if.then.i:
; CHECK-NEXT: tail call void @abort()
; CHECK-NEXT: unreachable
; CHECK: at.exit:
; CHECK-NEXT: [[K_07:%.*]] = phi i32 [ [[DEC:%.*]], [[FOR_BODY4]] ], [ [[I_09]], [[FOR_BODY4_PREHEADER]] ]
; CHECK-NEXT: [[IDX_EXT_I:%.*]] = zext i32 [[K_07]] to i64
; CHECK-NEXT: [[ADD_PTR_I:%.*]] = getelementptr inbounds i32, ptr [[ARR]], i64 [[IDX_EXT_I]]
; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[ADD_PTR_I]], align 4
Expand Down