[APInt] Add saturating left-shift 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 `shlWithNoWrap()`

Reviewers: spatel, nikic

Reviewed By: nikic

Subscribers: hiraditya, dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69398

3 files changed, 38 insertions, 0 deletions

diff --git a/llvm/include/llvm/ADT/APInt.h b/llvm/include/llvm/ADT/APInt.h
index ddf0e19..6a08e6e 100644
--- a/llvm/include/llvm/ADT/APInt.h
+++ b/llvm/include/llvm/ADT/APInt.h
@@ -1111,6 +1111,8 @@ public:
   APInt usub_sat(const APInt &RHS) const;
   APInt smul_sat(const APInt &RHS) const;
   APInt umul_sat(const APInt &RHS) const;
+  APInt sshl_sat(const APInt &RHS) const;
+  APInt ushl_sat(const APInt &RHS) const;
 
   /// Array-indexing support.
   ///
diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index df2e619..08e9757 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -2070,6 +2070,25 @@ APInt APInt::umul_sat(const APInt &RHS) const {
   return APInt::getMaxValue(BitWidth);
 }
 
+APInt APInt::sshl_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = sshl_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
+
+  return isNegative() ? APInt::getSignedMinValue(BitWidth)
+                      : APInt::getSignedMaxValue(BitWidth);
+}
+
+APInt APInt::ushl_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = ushl_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
   assert(!str.empty() && "Invalid string length");
diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
index f45a4e6..5130b94 100644
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -1215,6 +1215,23 @@ TEST(APIntTest, SaturatingMath) {
   EXPECT_EQ(APInt(8, -128), APInt(8, 25).smul_sat(APInt(8, -6)));
   EXPECT_EQ(APInt(8, 127), APInt(8, -25).smul_sat(APInt(8, -6)));
   EXPECT_EQ(APInt(8, 127), APInt(8, 25).smul_sat(APInt(8, 6)));
+
+  EXPECT_EQ(APInt(8, 128), APInt(8, 4).ushl_sat(APInt(8, 5)));
+  EXPECT_EQ(APInt(8, 255), APInt(8, 4).ushl_sat(APInt(8, 6)));
+  EXPECT_EQ(APInt(8, 128), APInt(8, 1).ushl_sat(APInt(8, 7)));
+  EXPECT_EQ(APInt(8, 255), APInt(8, 1).ushl_sat(APInt(8, 8)));
+  EXPECT_EQ(APInt(8, 255), APInt(8, -128).ushl_sat(APInt(8, 2)));
+  EXPECT_EQ(APInt(8, 255), APInt(8, 64).ushl_sat(APInt(8, 2)));
+  EXPECT_EQ(APInt(8, 255), APInt(8, 64).ushl_sat(APInt(8, -2)));
+
+  EXPECT_EQ(APInt(8, 64), APInt(8, 4).sshl_sat(APInt(8, 4)));
+  EXPECT_EQ(APInt(8, 127), APInt(8, 4).sshl_sat(APInt(8, 5)));
+  EXPECT_EQ(APInt(8, 127), APInt(8, 1).sshl_sat(APInt(8, 8)));
+  EXPECT_EQ(APInt(8, -64), APInt(8, -4).sshl_sat(APInt(8, 4)));
+  EXPECT_EQ(APInt(8, -128), APInt(8, -4).sshl_sat(APInt(8, 5)));
+  EXPECT_EQ(APInt(8, -128), APInt(8, -4).sshl_sat(APInt(8, 6)));
+  EXPECT_EQ(APInt(8, -128), APInt(8, -1).sshl_sat(APInt(8, 7)));
+  EXPECT_EQ(APInt(8, -128), APInt(8, -1).sshl_sat(APInt(8, 8)));
 }
 
 TEST(APIntTest, FromArray) {