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Teach ScalarEvolution to make use of no-overflow flags when
analyzing add recurrences. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77034 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -734,6 +734,13 @@ const SCEV *ScalarEvolution::getZeroExtendExpr(const SCEV *Op,
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unsigned BitWidth = getTypeSizeInBits(AR->getType());
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const Loop *L = AR->getLoop();
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// If we have special knowledge that this addrec won't overflow,
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// we don't need to do any further analysis.
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if (AR->hasNoUnsignedOverflow())
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return getAddRecExpr(getZeroExtendExpr(Start, Ty),
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getZeroExtendExpr(Step, Ty),
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L);
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// Check whether the backedge-taken count is SCEVCouldNotCompute.
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// Note that this serves two purposes: It filters out loops that are
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// simply not analyzable, and it covers the case where this code is
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@ -866,6 +873,13 @@ const SCEV *ScalarEvolution::getSignExtendExpr(const SCEV *Op,
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unsigned BitWidth = getTypeSizeInBits(AR->getType());
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const Loop *L = AR->getLoop();
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// If we have special knowledge that this addrec won't overflow,
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// we don't need to do any further analysis.
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if (AR->hasNoSignedOverflow())
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return getAddRecExpr(getSignExtendExpr(Start, Ty),
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getSignExtendExpr(Step, Ty),
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L);
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// Check whether the backedge-taken count is SCEVCouldNotCompute.
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// Note that this serves two purposes: It filters out loops that are
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// simply not analyzable, and it covers the case where this code is
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@ -2344,8 +2358,29 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
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cast<SCEVAddRecExpr>(Accum)->getLoop() == L)) {
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const SCEV *StartVal =
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getSCEV(PN->getIncomingValue(IncomingEdge));
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const SCEV *PHISCEV =
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getAddRecExpr(StartVal, Accum, L);
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const SCEVAddRecExpr *PHISCEV =
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cast<SCEVAddRecExpr>(getAddRecExpr(StartVal, Accum, L));
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// If the increment doesn't overflow, then neither the addrec nor the
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// post-increment will overflow.
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if (const AddOperator *OBO = dyn_cast<AddOperator>(BEValueV))
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if (OBO->getOperand(0) == PN &&
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getSCEV(OBO->getOperand(1)) ==
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PHISCEV->getStepRecurrence(*this)) {
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const SCEVAddRecExpr *PostInc = PHISCEV->getPostIncExpr(*this);
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if (OBO->hasNoUnsignedOverflow()) {
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const_cast<SCEVAddRecExpr *>(PHISCEV)
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->setHasNoUnsignedOverflow(true);
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const_cast<SCEVAddRecExpr *>(PostInc)
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->setHasNoUnsignedOverflow(true);
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}
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if (OBO->hasNoSignedOverflow()) {
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const_cast<SCEVAddRecExpr *>(PHISCEV)
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->setHasNoSignedOverflow(true);
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const_cast<SCEVAddRecExpr *>(PostInc)
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->setHasNoSignedOverflow(true);
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}
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}
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// Okay, for the entire analysis of this edge we assumed the PHI
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// to be symbolic. We now need to go back and purge all of the
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40
test/Analysis/ScalarEvolution/nsw.ll
Normal file
40
test/Analysis/ScalarEvolution/nsw.ll
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@ -0,0 +1,40 @@
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; RUN: llvm-as < %s | opt -analyze -scalar-evolution -disable-output | grep { --> {.*,+,.*}<bb>} | count 8
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; The addrecs in this loop are analyzable only by using nsw information.
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target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64"
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define void @foo(double* %p) nounwind {
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entry:
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%tmp = load double* %p, align 8 ; <double> [#uses=1]
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%tmp1 = fcmp ogt double %tmp, 2.000000e+00 ; <i1> [#uses=1]
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br i1 %tmp1, label %bb.nph, label %return
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bb.nph: ; preds = %entry
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br label %bb
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bb: ; preds = %bb1, %bb.nph
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%i.01 = phi i32 [ %tmp8, %bb1 ], [ 0, %bb.nph ] ; <i32> [#uses=3]
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%tmp2 = sext i32 %i.01 to i64 ; <i64> [#uses=1]
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%tmp3 = getelementptr double* %p, i64 %tmp2 ; <double*> [#uses=1]
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%tmp4 = load double* %tmp3, align 8 ; <double> [#uses=1]
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%tmp5 = fmul double %tmp4, 9.200000e+00 ; <double> [#uses=1]
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%tmp6 = sext i32 %i.01 to i64 ; <i64> [#uses=1]
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%tmp7 = getelementptr double* %p, i64 %tmp6 ; <double*> [#uses=1]
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store double %tmp5, double* %tmp7, align 8
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%tmp8 = nsw add i32 %i.01, 1 ; <i32> [#uses=2]
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br label %bb1
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bb1: ; preds = %bb
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%phitmp = sext i32 %tmp8 to i64 ; <i64> [#uses=1]
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%tmp9 = getelementptr double* %p, i64 %phitmp ; <double*> [#uses=1]
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%tmp10 = load double* %tmp9, align 8 ; <double> [#uses=1]
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%tmp11 = fcmp ogt double %tmp10, 2.000000e+00 ; <i1> [#uses=1]
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br i1 %tmp11, label %bb, label %bb1.return_crit_edge
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bb1.return_crit_edge: ; preds = %bb1
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br label %return
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return: ; preds = %bb1.return_crit_edge, %entry
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ret void
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}
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