[APInt] Add methods for saturated add and sub

This adds the sadd_sat, uadd_sat, ssub_sat, usub_sat methods for performing saturating additions and subtractions to APInt.

Split out from D54237.

Patch by: nikic (Nikita Popov)

Differential Revision: https://reviews.llvm.org/D54332

llvm-svn: 347324

1 files changed, 36 insertions, 0 deletions

diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index f2f5cca..a5f4f98 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -1947,7 +1947,43 @@ APInt APInt::ushl_ov(const APInt &ShAmt, bool &Overflow) const {
   return *this << ShAmt;
 }
 
+APInt APInt::sadd_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = sadd_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
 
+  return isNegative() ? APInt::getSignedMinValue(BitWidth)
+                      : APInt::getSignedMaxValue(BitWidth);
+}
+
+APInt APInt::uadd_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = uadd_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
+
+  return APInt::getMaxValue(BitWidth);
+}
+
+APInt APInt::ssub_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = ssub_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
+
+  return isNegative() ? APInt::getSignedMinValue(BitWidth)
+                      : APInt::getSignedMaxValue(BitWidth);
+}
+
+APInt APInt::usub_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = usub_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
+
+  return APInt(BitWidth, 0);
+}
 
 
 void APInt::fromString(unsigned numbits, StringRef str, uint8_t radix) {