[SCEV] Strengthen StrengthenNoWrapFlags (reapply r334428).

Summary:
Comment on Transforms/LoopVersioning/incorrect-phi.ll: With the change
SCEV is able to prove that the loop doesn't wrap-self (due to zext i16
to i64), disabling the entire loop versioning pass. Removed the zext and
just use i64.

Reviewers: sanjoy

Subscribers: jlebar, hiraditya, javed.absar, bixia, llvm-commits

Differential Revision: https://reviews.llvm.org/D48409

llvm-svn: 336140

1 files changed, 20 insertions, 7 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index d52c5b0276a..a39ac9b9fb9 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -2247,22 +2247,35 @@ StrengthenNoWrapFlags(ScalarEvolution *SE, SCEVTypes Type,
 
   SignOrUnsignWrap = ScalarEvolution::maskFlags(Flags, SignOrUnsignMask);
 
-  if (SignOrUnsignWrap != SignOrUnsignMask && Type == scAddExpr &&
-      Ops.size() == 2 && isa<SCEVConstant>(Ops[0])) {
-
-    // (A + C) --> (A + C)<nsw> if the addition does not sign overflow
-    // (A + C) --> (A + C)<nuw> if the addition does not unsign overflow
+  if (SignOrUnsignWrap != SignOrUnsignMask &&
+      (Type == scAddExpr || Type == scMulExpr) && Ops.size() == 2 &&
+      isa<SCEVConstant>(Ops[0])) {
+
+    auto Opcode = [&] {
+      switch (Type) {
+      case scAddExpr:
+        return Instruction::Add;
+      case scMulExpr:
+        return Instruction::Mul;
+      default:
+        llvm_unreachable("Unexpected SCEV op.");
+      }
+    }();
 
     const APInt &C = cast<SCEVConstant>(Ops[0])->getAPInt();
+
+    // (A <opcode> C) --> (A <opcode> C)<nsw> if the op doesn't sign overflow.
     if (!(SignOrUnsignWrap & SCEV::FlagNSW)) {
       auto NSWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
-          Instruction::Add, C, OBO::NoSignedWrap);
+          Opcode, C, OBO::NoSignedWrap);
       if (NSWRegion.contains(SE->getSignedRange(Ops[1])))
         Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
     }
+
+    // (A <opcode> C) --> (A <opcode> C)<nuw> if the op doesn't unsign overflow.
     if (!(SignOrUnsignWrap & SCEV::FlagNUW)) {
       auto NUWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
-          Instruction::Add, C, OBO::NoUnsignedWrap);
+          Opcode, C, OBO::NoUnsignedWrap);
       if (NUWRegion.contains(SE->getUnsignedRange(Ops[1])))
         Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
     }