[ScalarEvolution] Strictly enforce pointer/int type rules.

Rules:

1. SCEVUnknown is a pointer if and only if the LLVM IR value is a
   pointer.
2. SCEVPtrToInt is never a pointer.
3. If any other SCEV expression has no pointer operands, the result is
   an integer.
4. If a SCEVAddExpr has exactly one pointer operand, the result is a
   pointer.
5. If a SCEVAddRecExpr's first operand is a pointer, and it has no other
   pointer operands, the result is a pointer.
6. If every operand of a SCEVMinMaxExpr is a pointer, the result is a
   pointer.
7. Otherwise, the SCEV expression is invalid.

I'm not sure how useful rule 6 is in practice.  If we exclude it, we can
guarantee that ScalarEvolution::getPointerBase always returns a
SCEVUnknown, which might be a helpful property. Anyway, I'll leave that
for a followup.

This is basically mop-up at this point; all the changes with significant
functional effects have landed.  Some of the remaining changes could be
split off, but I don't see much point.

Differential Revision: https://reviews.llvm.org/D105510

1 files changed, 7 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index 1cf3f97..5af1c37 100644
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -1147,6 +1147,10 @@ static bool canBeCheaplyTransformed(ScalarEvolution &SE,
                                     const SCEVAddRecExpr *Phi,
                                     const SCEVAddRecExpr *Requested,
                                     bool &InvertStep) {
+  // We can't transform to match a pointer PHI.
+  if (Phi->getType()->isPointerTy())
+    return false;
+
   Type *PhiTy = SE.getEffectiveSCEVType(Phi->getType());
   Type *RequestedTy = SE.getEffectiveSCEVType(Requested->getType());
 
@@ -1165,8 +1169,7 @@ static bool canBeCheaplyTransformed(ScalarEvolution &SE,
   }
 
   // Check whether inverting will help: {R,+,-1} == R - {0,+,1}.
-  if (SE.getAddExpr(Requested->getStart(),
-                    SE.getNegativeSCEV(Requested)) == Phi) {
+  if (SE.getMinusSCEV(Requested->getStart(), Requested) == Phi) {
     InvertStep = true;
     return true;
   }
@@ -1577,8 +1580,8 @@ Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
   // Rewrite an AddRec in terms of the canonical induction variable, if
   // its type is more narrow.
   if (CanonicalIV &&
-      SE.getTypeSizeInBits(CanonicalIV->getType()) >
-      SE.getTypeSizeInBits(Ty)) {
+      SE.getTypeSizeInBits(CanonicalIV->getType()) > SE.getTypeSizeInBits(Ty) &&
+      !S->getType()->isPointerTy()) {
     SmallVector<const SCEV *, 4> NewOps(S->getNumOperands());
     for (unsigned i = 0, e = S->getNumOperands(); i != e; ++i)
       NewOps[i] = SE.getAnyExtendExpr(S->op_begin()[i], CanonicalIV->getType());