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If the step value is a constant zero, the loop isn't going to terminate. Fixes

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the assert reported in PR13228!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159393 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2012-06-28 23:44:57 +00:00
parent 917f97c580
commit 4d3bba5be4
2 changed files with 28 additions and 1 deletions
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2
lib/Analysis/ScalarEvolution.cpp
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@ -5484,7 +5484,7 @@ ScalarEvolution::HowFarToZero(const SCEV *V, const Loop *L) {
// to 0, it must be counting down to equal 0. Consequently, N = Start / -Step.
// We have not yet seen any such cases.
const SCEVConstant *StepC = dyn_cast<SCEVConstant>(Step);
if (StepC == 0)
if (StepC == 0 || StepC->getValue()->equalsInt(0))
return getCouldNotCompute();
// For positive steps (counting up until unsigned overflow):

27
test/Analysis/ScalarEvolution/how-far-to-zero.ll Normal file
View File

@ -0,0 +1,27 @@
; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
; PR13228
define void @f() nounwind uwtable readnone {
entry:
br label %for.cond
for.cond: ; preds = %for.cond, %entry
%c.0 = phi i8 [ 1, %entry ], [ 0, %for.cond ]
%i.0 = phi i8 [ 0, %entry ], [ %inc, %for.cond ]
%lnot = icmp eq i8 %i.0, 0
%inc = add i8 %i.0, 1
br i1 %lnot, label %for.cond, label %while.cond
while.cond: ; preds = %while.body, %for.cond
%b.2 = phi i8 [ %add, %while.body ], [ 0, %for.cond ]
br i1 undef, label %while.end, label %while.body
while.body: ; preds = %while.cond
%add = add i8 %b.2, %c.0
%tobool7 = icmp eq i8 %add, 0
br i1 %tobool7, label %while.end, label %while.cond
while.end: ; preds = %while.body, %while.cond
ret void
}
;CHECK: Loop %while.cond: <multiple exits> Unpredictable backedge-taken count.