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[SCEV] Apply guards to max with non-unitary steps.

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We already apply loop-guards when computing the maximum with unitary
steps. This extends the code to also do so when dealing with non-unitary
steps.

This allows us to infer a tighter maximum in some cases.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D102267
This commit is contained in:
Florian Hahn 2021-05-13 09:32:41 +01:00
parent 01960a7ab2
commit 8bc2e95e00
2 changed files with 12 additions and 7 deletions
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13
lib/Analysis/ScalarEvolution.cpp
View File

@ -9262,10 +9262,15 @@ ScalarEvolution::howFarToZero(const SCEV *V, const Loop *L, bool ControlsExit,
loopHasNoAbnormalExits(AddRec->getLoop())) {
const SCEV *Exact =
getUDivExpr(Distance, CountDown ? getNegativeSCEV(Step) : Step);
const SCEV *Max =
Exact == getCouldNotCompute()
? Exact
: getConstant(getUnsignedRangeMax(Exact));
const SCEV *Max = getCouldNotCompute();
if (Exact != getCouldNotCompute()) {
APInt MaxInt = getUnsignedRangeMax(applyLoopGuards(Exact, L));
APInt BaseMaxInt = getUnsignedRangeMax(Exact);
if (BaseMaxInt.ult(MaxInt))
Max = getConstant(BaseMaxInt);
else
Max = getConstant(MaxInt);
}
return ExitLimit(Exact, Max, false, Predicates);
}

6
test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
View File

@ -200,14 +200,14 @@ define void @test_guard_ule_12_step2(i32* nocapture %a, i64 %N) {
; CHECK-LABEL: 'test_guard_ule_12_step2'
; CHECK-NEXT: Classifying expressions for: @test_guard_ule_12_step2
; CHECK-NEXT: %iv = phi i64 [ %iv.next, %loop ], [ 0, %entry ]
; CHECK-NEXT: --> {0,+,2}<nuw><nsw><%loop> U: [0,-9223372036854775808) S: [0,9223372036854775807) Exits: (2 * (%N /u 2))<nuw> LoopDispositions: { %loop: Computable }
; CHECK-NEXT: --> {0,+,2}<nuw><nsw><%loop> U: [0,13) S: [0,13) Exits: (2 * (%N /u 2))<nuw> LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %idx = getelementptr inbounds i32, i32* %a, i64 %iv
; CHECK-NEXT: --> {%a,+,8}<nuw><%loop> U: full-set S: full-set Exits: ((8 * (%N /u 2)) + %a) LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.next = add nuw nsw i64 %iv, 2
; CHECK-NEXT: --> {2,+,2}<nuw><%loop> U: [2,-1) S: [-9223372036854775808,9223372036854775807) Exits: (2 + (2 * (%N /u 2))<nuw>) LoopDispositions: { %loop: Computable }
; CHECK-NEXT: --> {2,+,2}<nuw><nsw><%loop> U: [2,15) S: [2,15) Exits: (2 + (2 * (%N /u 2))<nuw>) LoopDispositions: { %loop: Computable }
; CHECK-NEXT: Determining loop execution counts for: @test_guard_ule_12_step2
; CHECK-NEXT: Loop %loop: backedge-taken count is (%N /u 2)
; CHECK-NEXT: Loop %loop: max backedge-taken count is 9223372036854775807
; CHECK-NEXT: Loop %loop: max backedge-taken count is 6
; CHECK-NEXT: Loop %loop: Predicated backedge-taken count is (%N /u 2)
; CHECK-NEXT: Predicates:
; CHECK: Loop %loop: Trip multiple is 1