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
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index c77c7c4..49af579 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -734,6 +734,13 @@
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 @@
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 @@
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
diff --git a/test/Analysis/ScalarEvolution/nsw.ll b/test/Analysis/ScalarEvolution/nsw.ll
new file mode 100644
index 0000000..245ed6f
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/nsw.ll
@@ -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
+}