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[ConstraintElim] Use cond from header as upper bound on IV in exit BB. #94610

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Merged
merged 4 commits into from
Jul 9, 2024
Merged

[ConstraintElim] Use cond from header as upper bound on IV in exit BB. #94610

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8310ce6
[ConstraintElim] Use cond from header as upper bound on IV in exit BB.
fhahn Jun 6, 2024
474acb5
!fixup properly handle non-monotonically increasing case.
fhahn Jun 6, 2024
d51a036
!fixup always emit precondition, don't check unique predecessor
fhahn Jun 28, 2024
e1af9a5
Merge branch 'main' into ce-loop-header-exit
fhahn Jul 9, 2024
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14 changes: 14 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 @@ -1032,6 +1032,20 @@ void State::addInfoForInductions(BasicBlock &BB) {
WorkList.push_back(FactOrCheck::getConditionFact(
DTN, CmpInst::ICMP_SLT, PN, B,
ConditionTy(CmpInst::ICMP_SLE, StartValue, B)));

// Try to add condition from header to the exit blocks. When exiting either
// with EQ or NE in the header, we know that the induction value must be u<=
// B, as other exits may only exit earlier.
assert(!StepOffset.isNegative() && "induction must be increasing");
assert((Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_NE) &&
"unsupported predicate");
ConditionTy Precond = {CmpInst::ICMP_ULE, StartValue, B};
SmallVector<BasicBlock *> ExitBBs;
L->getExitBlocks(ExitBBs);
for (BasicBlock *EB : ExitBBs) {
WorkList.emplace_back(FactOrCheck::getConditionFact(
DT.getNode(EB), CmpInst::ICMP_ULE, A, B, Precond));
}
}

void State::addInfoFor(BasicBlock &BB) {
Expand Down
15 changes: 5 additions & 10 deletions llvm/test/Transforms/ConstraintElimination/induction-condition-in-loop-exit.ll
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Expand Up @@ -19,8 +19,7 @@ define i1 @multi_exiting_loop_eq_same_unique_exit_const_compare_known(ptr %s) {
; CHECK-NEXT: [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
; CHECK-NEXT: br i1 [[LATCH_C]], label %[[LOOP_HEADER]], label %[[EXIT]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: [[T:%.*]] = icmp ult i32 [[IV]], 1235
; CHECK-NEXT: ret i1 [[T]]
; CHECK-NEXT: ret i1 true
;
entry:
br label %loop.header
Expand Down Expand Up @@ -99,8 +98,7 @@ define i1 @multi_exiting_loop_eq_same_unique_exit_const_compare_known_due_to_pre
; CHECK-NEXT: [[IV_NEXT]] = add i32 [[IV]], 1
; CHECK-NEXT: br i1 [[LATCH_C]], label %[[LOOP_HEADER]], label %[[EXIT]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: [[T:%.*]] = icmp ult i32 [[IV]], 1235
; CHECK-NEXT: ret i1 [[T]]
; CHECK-NEXT: ret i1 true
;
entry:
%pre.c = icmp ule i32 %start, 1234
Expand Down Expand Up @@ -341,8 +339,7 @@ define i1 @multi_exiting_loop_eq_same_unique_exit_var_compare_known(ptr %s, i32
; CHECK-NEXT: [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
; CHECK-NEXT: br i1 [[LATCH_C]], label %[[LOOP_HEADER]], label %[[EXIT]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: [[T:%.*]] = icmp ule i32 [[IV]], [[N]]
; CHECK-NEXT: ret i1 [[T]]
; CHECK-NEXT: ret i1 true
;
entry:
br label %loop.header
Expand Down Expand Up @@ -419,8 +416,7 @@ define i1 @multi_exiting_loop_ne_same_unique_exit_const_compare_known(ptr %s) {
; CHECK-NEXT: [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
; CHECK-NEXT: br i1 [[LATCH_C]], label %[[LOOP_HEADER]], label %[[EXIT]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: [[T:%.*]] = icmp ult i32 [[IV]], 1235
; CHECK-NEXT: ret i1 [[T]]
; CHECK-NEXT: ret i1 true
;
entry:
br label %loop.header
Expand Down Expand Up @@ -545,8 +541,7 @@ define i1 @multi_exiting_loop_eq_different_exits_2_const_compare_known(ptr %s, i
; CHECK-NEXT: [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
; CHECK-NEXT: br i1 [[LATCH_C]], label %[[LOOP_HEADER]], label %[[EXIT_2]]
; CHECK: [[EXIT_1]]:
; CHECK-NEXT: [[T_1:%.*]] = icmp ult i32 [[IV]], 1235
; CHECK-NEXT: ret i1 [[T_1]]
; CHECK-NEXT: ret i1 true
; CHECK: [[EXIT_2]]:
; CHECK-NEXT: ret i1 true
;
Expand Down