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ScalarEvolution: HowFarToZero was wrongly using signed division

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HowFarToZero was supposed to use unsigned division in order to calculate
the backedge taken count.  However, SCEVDivision::divide performs signed
division.  Unless I am mistaken, no users of SCEVDivision actually want
signed arithmetic: switch to udiv and urem.

This fixes PR21578.

llvm-svn: 222093
This commit is contained in:
David Majnemer 2014-11-16 07:30:35 +00:00
parent 12827e608f
commit 7e29d637c6
2 changed files with 12 additions and 12 deletions
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20
lib/Analysis/ScalarEvolution.cpp
View File

@ -675,32 +675,32 @@ static void GroupByComplexity(SmallVectorImpl<const SCEV *> &Ops,
}
}
static const APInt srem(const SCEVConstant *C1, const SCEVConstant *C2) {
static const APInt urem(const SCEVConstant *C1, const SCEVConstant *C2) {
APInt A = C1->getValue()->getValue();
APInt B = C2->getValue()->getValue();
uint32_t ABW = A.getBitWidth();
uint32_t BBW = B.getBitWidth();
if (ABW > BBW)
B = B.sext(ABW);
B = B.zext(ABW);
else if (ABW < BBW)
A = A.sext(BBW);
A = A.zext(BBW);
return APIntOps::srem(A, B);
return APIntOps::urem(A, B);
}
static const APInt sdiv(const SCEVConstant *C1, const SCEVConstant *C2) {
static const APInt udiv(const SCEVConstant *C1, const SCEVConstant *C2) {
APInt A = C1->getValue()->getValue();
APInt B = C2->getValue()->getValue();
uint32_t ABW = A.getBitWidth();
uint32_t BBW = B.getBitWidth();
if (ABW > BBW)
B = B.sext(ABW);
B = B.zext(ABW);
else if (ABW < BBW)
A = A.sext(BBW);
A = A.zext(BBW);
return APIntOps::sdiv(A, B);
return APIntOps::udiv(A, B);
}
namespace {
@ -803,8 +803,8 @@ public:
void visitConstant(const SCEVConstant *Numerator) {
if (const SCEVConstant *D = dyn_cast<SCEVConstant>(Denominator)) {
Quotient = SE.getConstant(sdiv(Numerator, D));
Remainder = SE.getConstant(srem(Numerator, D));
Quotient = SE.getConstant(udiv(Numerator, D));
Remainder = SE.getConstant(urem(Numerator, D));
return;
}
}

4
test/Analysis/ScalarEvolution/trip-count-pow2.ll
View File

@ -48,6 +48,6 @@ exit:
ret void
; CHECK-LABEL: @test3
; CHECK: Loop %loop: backedge-taken count is ((-96 + (96 * %n)) /u 96)
; CHECK: Loop %loop: max backedge-taken count is ((-96 + (96 * %n)) /u 96)
; CHECK: Loop %loop: Unpredictable backedge-taken count.
; CHECK: Loop %loop: Unpredictable max backedge-taken count.
}