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Teach ScalarEvolution to make use of no-overflow flags when

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analyzing add recurrences.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77034 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-07-25 01:22:26 +00:00
parent 6c1980b335
commit eb490a7aa3
2 changed files with 77 additions and 2 deletions
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39
lib/Analysis/ScalarEvolution.cpp
View File

@ -734,6 +734,13 @@ const SCEV *ScalarEvolution::getZeroExtendExpr(const SCEV *Op,
unsigned BitWidth = getTypeSizeInBits(AR->getType());
const Loop *L = AR->getLoop();
// If we have special knowledge that this addrec won't overflow,
// we don't need to do any further analysis.
if (AR->hasNoUnsignedOverflow())
return getAddRecExpr(getZeroExtendExpr(Start, Ty),
getZeroExtendExpr(Step, Ty),
L);
// Check whether the backedge-taken count is SCEVCouldNotCompute.
// Note that this serves two purposes: It filters out loops that are
// simply not analyzable, and it covers the case where this code is
@ -866,6 +873,13 @@ const SCEV *ScalarEvolution::getSignExtendExpr(const SCEV *Op,
unsigned BitWidth = getTypeSizeInBits(AR->getType());
const Loop *L = AR->getLoop();
// If we have special knowledge that this addrec won't overflow,
// we don't need to do any further analysis.
if (AR->hasNoSignedOverflow())
return getAddRecExpr(getSignExtendExpr(Start, Ty),
getSignExtendExpr(Step, Ty),
L);
// Check whether the backedge-taken count is SCEVCouldNotCompute.
// Note that this serves two purposes: It filters out loops that are
// simply not analyzable, and it covers the case where this code is
@ -2344,8 +2358,29 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
cast<SCEVAddRecExpr>(Accum)->getLoop() == L)) {
const SCEV *StartVal =
getSCEV(PN->getIncomingValue(IncomingEdge));
const SCEV *PHISCEV =
getAddRecExpr(StartVal, Accum, L);
const SCEVAddRecExpr *PHISCEV =
cast<SCEVAddRecExpr>(getAddRecExpr(StartVal, Accum, L));
// If the increment doesn't overflow, then neither the addrec nor the
// post-increment will overflow.
if (const AddOperator *OBO = dyn_cast<AddOperator>(BEValueV))
if (OBO->getOperand(0) == PN &&
getSCEV(OBO->getOperand(1)) ==
PHISCEV->getStepRecurrence(*this)) {
const SCEVAddRecExpr *PostInc = PHISCEV->getPostIncExpr(*this);
if (OBO->hasNoUnsignedOverflow()) {
const_cast<SCEVAddRecExpr *>(PHISCEV)
->setHasNoUnsignedOverflow(true);
const_cast<SCEVAddRecExpr *>(PostInc)
->setHasNoUnsignedOverflow(true);
}
if (OBO->hasNoSignedOverflow()) {
const_cast<SCEVAddRecExpr *>(PHISCEV)
->setHasNoSignedOverflow(true);
const_cast<SCEVAddRecExpr *>(PostInc)
->setHasNoSignedOverflow(true);
}
}
// Okay, for the entire analysis of this edge we assumed the PHI
// to be symbolic. We now need to go back and purge all of the

40
test/Analysis/ScalarEvolution/nsw.ll Normal file
View File

@ -0,0 +1,40 @@
; RUN: llvm-as < %s | opt -analyze -scalar-evolution -disable-output | grep { --> {.*,+,.*}<bb>} | count 8
; The addrecs in this loop are analyzable only by using nsw information.
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64"
define void @foo(double* %p) nounwind {
entry:
%tmp = load double* %p, align 8 ; <double> [#uses=1]
%tmp1 = fcmp ogt double %tmp, 2.000000e+00 ; <i1> [#uses=1]
br i1 %tmp1, label %bb.nph, label %return
bb.nph: ; preds = %entry
br label %bb
bb: ; preds = %bb1, %bb.nph
%i.01 = phi i32 [ %tmp8, %bb1 ], [ 0, %bb.nph ] ; <i32> [#uses=3]
%tmp2 = sext i32 %i.01 to i64 ; <i64> [#uses=1]
%tmp3 = getelementptr double* %p, i64 %tmp2 ; <double*> [#uses=1]
%tmp4 = load double* %tmp3, align 8 ; <double> [#uses=1]
%tmp5 = fmul double %tmp4, 9.200000e+00 ; <double> [#uses=1]
%tmp6 = sext i32 %i.01 to i64 ; <i64> [#uses=1]
%tmp7 = getelementptr double* %p, i64 %tmp6 ; <double*> [#uses=1]
store double %tmp5, double* %tmp7, align 8
%tmp8 = nsw add i32 %i.01, 1 ; <i32> [#uses=2]
br label %bb1
bb1: ; preds = %bb
%phitmp = sext i32 %tmp8 to i64 ; <i64> [#uses=1]
%tmp9 = getelementptr double* %p, i64 %phitmp ; <double*> [#uses=1]
%tmp10 = load double* %tmp9, align 8 ; <double> [#uses=1]
%tmp11 = fcmp ogt double %tmp10, 2.000000e+00 ; <i1> [#uses=1]
br i1 %tmp11, label %bb, label %bb1.return_crit_edge
bb1.return_crit_edge: ; preds = %bb1
br label %return
return: ; preds = %bb1.return_crit_edge, %entry
ret void
}