[SCEV] Add nuw/nsw to mul ops in StrengthenNoWrapFlags where safe.

Summary:
Previously we would add them for adds, but not multiplies.

Reviewers: sanjoy

Subscribers: llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D48038

llvm-svn: 334428

1 files changed, 19 insertions, 6 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index a48b935f88a..dee35392692 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -2205,19 +2205,32 @@ 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);