[APInt] Add saturating multiply ops

Summary:
There are `*_ov()` functions already, so at least for consistency it may be good to also have saturating variants.
These may or may not be needed for `ConstantRange`'s `mulWithNoWrap()`

Reviewers: spatel, nikic

Reviewed By: nikic

Subscribers: hiraditya, dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69397

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index 758fe8b4f86..df2e6197b2a 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -2048,6 +2048,27 @@ APInt APInt::usub_sat(const APInt &RHS) const {
   return APInt(BitWidth, 0);
 }
 
+APInt APInt::smul_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = smul_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
+
+  // The result is negative if one and only one of inputs is negative.
+  bool ResIsNegative = isNegative() ^ RHS.isNegative();
+
+  return ResIsNegative ? APInt::getSignedMinValue(BitWidth)
+                       : APInt::getSignedMaxValue(BitWidth);
+}
+
+APInt APInt::umul_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = umul_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
+
+  return APInt::getMaxValue(BitWidth);
+}
 
 void APInt::fromString(unsigned numbits, StringRef str, uint8_t radix) {
   // Check our assumptions here