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[SCEV] Improve Scalar Evolution's use of no {un,}signed wrap flags

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In a case where we have a no {un,}signed wrap flag on the increment, if
RHS - Start is constant then we can avoid inserting a max operation bewteen
the two, since we can statically determine which is greater.

This allows us to unroll loops such as:

 void testcase3(int v) {
   for (int i=v; i<=v+1; ++i)
     f(i);
 }


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220960 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bradley Smith
2014-10-31 11:40:32 +00:00
parent 8a9c531e9a
commit 8cff277de2
3 changed files with 79 additions and 8 deletions
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lib/Analysis/ScalarEvolution.cpp
+26 -6
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@@ -6964,9 +6964,19 @@ ScalarEvolution::HowManyLessThans(const SCEV *LHS, const SCEV *RHS,
: ICmpInst::ICMP_ULT;
const SCEV *Start = IV->getStart();
const SCEV *End = RHS;
if (!isLoopEntryGuardedByCond(L, Cond, getMinusSCEV(Start, Stride), RHS))
End = IsSigned ? getSMaxExpr(RHS, Start)
: getUMaxExpr(RHS, Start);
if (!isLoopEntryGuardedByCond(L, Cond, getMinusSCEV(Start, Stride), RHS)) {
const SCEV *Diff = getMinusSCEV(RHS, Start);
// If we have NoWrap set, then we can assume that the increment won't
// overflow, in which case if RHS - Start is a constant, we don't need to
// do a max operation since we can just figure it out statically
if (NoWrap && isa<SCEVConstant>(Diff)) {
APInt D = dyn_cast<const SCEVConstant>(Diff)->getValue()->getValue();
if (D.isNegative())
End = Start;
} else
End = IsSigned ? getSMaxExpr(RHS, Start)
: getUMaxExpr(RHS, Start);
}
const SCEV *BECount = computeBECount(getMinusSCEV(End, Start), Stride, false);
@@ -7035,9 +7045,19 @@ ScalarEvolution::HowManyGreaterThans(const SCEV *LHS, const SCEV *RHS,
const SCEV *Start = IV->getStart();
const SCEV *End = RHS;
if (!isLoopEntryGuardedByCond(L, Cond, getAddExpr(Start, Stride), RHS))
End = IsSigned ? getSMinExpr(RHS, Start)
: getUMinExpr(RHS, Start);
if (!isLoopEntryGuardedByCond(L, Cond, getAddExpr(Start, Stride), RHS)) {
const SCEV *Diff = getMinusSCEV(RHS, Start);
// If we have NoWrap set, then we can assume that the increment won't
// overflow, in which case if RHS - Start is a constant, we don't need to
// do a max operation since we can just figure it out statically
if (NoWrap && isa<SCEVConstant>(Diff)) {
APInt D = dyn_cast<const SCEVConstant>(Diff)->getValue()->getValue();
if (!D.isNegative())
End = Start;
} else
End = IsSigned ? getSMinExpr(RHS, Start)
: getUMinExpr(RHS, Start);
}
const SCEV *BECount = computeBECount(getMinusSCEV(Start, End), Stride, false);