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[DA] getBackedgeTakenCount in isKnownLessThan can return CouldNotCompute #162495

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[DA] getBackedgeTakenCount in isKnownLessThan can return CouldNotCompute #162495

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2 changes: 2 additions & 0 deletions llvm/lib/Analysis/DependenceAnalysis.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1184,6 +1184,8 @@ bool DependenceInfo::isKnownLessThan(const SCEV *S, const SCEV *Size) const {
if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(S))
if (AddRec->isAffine() && AddRec->hasNoSignedWrap()) {
const SCEV *BECount = SE->getBackedgeTakenCount(AddRec->getLoop());
if (isa<SCEVCouldNotCompute>(BECount))
return false;
const SCEV *Start = AddRec->getStart();
const SCEV *Step = AddRec->getStepRecurrence(*SE);
const SCEV *End = AddRec->evaluateAtIteration(BECount, *SE);
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25 changes: 25 additions & 0 deletions llvm/test/Analysis/DependenceAnalysis/becount-couldnotcompute.ll
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@@ -0,0 +1,25 @@
; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 6
; RUN: opt < %s -disable-output "-passes=print<da>" -aa-pipeline=basic-aa 2>&1 | FileCheck %s

target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32"
target triple = "aarch64-unknown-linux-gnu"

; Test for function isKnownLessThan that calculates a back-edge taken count,
; which can return a CouldNotCompute SCEV.

define void @test(i64 %conv, ptr %a) {
; CHECK-LABEL: 'test'
; CHECK-NEXT: Src: %.pre.pre.pre = load i32, ptr %arrayidx12, align 4 --> Dst: %.pre.pre.pre = load i32, ptr %arrayidx12, align 4
; CHECK-NEXT: da analyze - none!
;
entry:
%sub = add i64 %conv, 1
br label %for.cond

for.cond:
%i.0 = phi i64 [ %add26, %for.cond ], [ 0, %entry ]
%arrayidx12 = getelementptr i32, ptr %a, i64 %i.0
%.pre.pre.pre = load i32, ptr %arrayidx12, align 4
%add26 = add nsw i64 %sub, %i.0
br label %for.cond
}