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Stay rational; don't assert trying to take the square root of a negative value.

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If it's negative, the loop is already proven to be infinite. Fixes PR13489!

llvm-svn: 161107
This commit is contained in:
Nick Lewycky 2012-08-01 09:14:36 +00:00
parent 892c043c64
commit e84df7229f
2 changed files with 27 additions and 0 deletions
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6
lib/Analysis/ScalarEvolution.cpp
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@ -5370,6 +5370,12 @@ SolveQuadraticEquation(const SCEVAddRecExpr *AddRec, ScalarEvolution &SE) {
SqrtTerm *= B;
SqrtTerm -= Four * (A * C);
if (SqrtTerm.isNegative()) {
// The loop is provably infinite.
const SCEV *CNC = SE.getCouldNotCompute();
return std::make_pair(CNC, CNC);
}
// Compute sqrt(B^2-4ac). This is guaranteed to be the nearest
// integer value or else APInt::sqrt() will assert.
APInt SqrtVal(SqrtTerm.sqrt());

21
test/Analysis/ScalarEvolution/SolveQuadraticEquation.ll
View File

@ -80,3 +80,24 @@ for.cond539.preheader:
unreachable
}
; CHECK: Determining loop execution counts for: @test3
; PR13489
; We used to crash on this too.
define void @test4() {
entry:
br label %for.body
for.body: ; preds = %for.body, %entry
%v2.02 = phi i64 [ 2, %entry ], [ %phitmp, %for.body ]
%v1.01 = phi i64 [ -2, %entry ], [ %sub1, %for.body ]
%sub1 = sub i64 %v1.01, %v2.02
%phitmp = add i64 %v2.02, 2
%tobool = icmp eq i64 %sub1, %phitmp
br i1 %tobool, label %for.end, label %for.body
for.end: ; preds = %for.body
ret void
}
; CHECK: Determining loop execution counts for: @test4