Added isValidRewrite() to check the result of ScalarEvolutionExpander.

SCEV may generate expressions composed of multiple pointers, which can
lead to invalid GEP expansion. Until we can teach SCEV to follow strict
pointer rules, make sure no bad GEPs creep into IR.
Fixes rdar://problem/9038671.

llvm-svn: 127839

1 files changed, 30 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 926d8c2..228974d 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -2718,6 +2718,36 @@ const SCEV *ScalarEvolution::getUMinFromMismatchedTypes(const SCEV *LHS,
   return getUMinExpr(PromotedLHS, PromotedRHS);
 }
 
+/// getPointerBase - Transitively follow the chain of pointer-type operands
+/// until reaching a SCEV that does not have a single pointer operand. This
+/// returns a SCEVUnknown pointer for well-formed pointer-type expressions,
+/// but corner cases do exist.
+const SCEV *ScalarEvolution::getPointerBase(const SCEV *V) {
+  // A pointer operand may evaluate to a nonpointer expression, such as null.
+  if (!V->getType()->isPointerTy())
+    return V;
+
+  if (const SCEVCastExpr *Cast = dyn_cast<SCEVCastExpr>(V)) {
+    return getPointerBase(Cast->getOperand());
+  }
+  else if (const SCEVNAryExpr *NAry = dyn_cast<SCEVNAryExpr>(V)) {
+    const SCEV *PtrOp = 0;
+    for (SCEVNAryExpr::op_iterator I = NAry->op_begin(), E = NAry->op_end();
+         I != E; ++I) {
+      if ((*I)->getType()->isPointerTy()) {
+        // Cannot find the base of an expression with multiple pointer operands.
+        if (PtrOp)
+          return V;
+        PtrOp = *I;
+      }
+    }
+    if (!PtrOp)
+      return V;
+    return getPointerBase(PtrOp);
+  }
+  return V;
+}
+
 /// PushDefUseChildren - Push users of the given Instruction
 /// onto the given Worklist.
 static void