When forming an addrec out of a phi don't just look at the last computation and steal its flags for our own, there may be other computations in the middle. Check whether the LHS of the computation is the phi itself and then we know it's safe to steal the flags. Fixes PR22795.

There's a missed optimization opportunity where we could look at the full chain of computation and take the intersection of the flags instead of only looking one instruction deep.

llvm-svn: 232134

1 files changed, 7 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index dcff7b60fb7..dfef7296848 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3591,10 +3591,12 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
               // 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->hasNoUnsignedWrap())
-                  Flags = setFlags(Flags, SCEV::FlagNUW);
-                if (OBO->hasNoSignedWrap())
-                  Flags = setFlags(Flags, SCEV::FlagNSW);
+                if (OBO->getOperand(0) == PN) {
+                  if (OBO->hasNoUnsignedWrap())
+                    Flags = setFlags(Flags, SCEV::FlagNUW);
+                  if (OBO->hasNoSignedWrap())
+                    Flags = setFlags(Flags, SCEV::FlagNSW);
+                }
               } else if (GEPOperator *GEP = dyn_cast<GEPOperator>(BEValueV)) {
                 // If the increment is an inbounds GEP, then we know the address
                 // space cannot be wrapped around. We cannot make any guarantee
@@ -3602,7 +3604,7 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
                 // unsigned but we may have a negative index from the base
                 // pointer. We can guarantee that no unsigned wrap occurs if the
                 // indices form a positive value.
-                if (GEP->isInBounds()) {
+                if (GEP->isInBounds() && GEP->getOperand(0) == PN) {
                   Flags = setFlags(Flags, SCEV::FlagNW);
 
                   const SCEV *Ptr = getSCEV(GEP->getPointerOperand());