[APInt} Add saturating left-shift ops

[lebedev.ri]

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()

[nikic]

LGTM

llvm/unittests/ADT/APIntTest.cpp

1225

It's a bit weird that out-of-bounds shift amounts have well-defined behavior here, but as this is an existing behavior of shl_ov, I guess it makes sense.

llvm/include/llvm/ADT/APInt.h

#endif
 
   // Operations that saturate
   APInt sadd_sat(const APInt &RHS) const;
   APInt uadd_sat(const APInt &RHS) const;
   APInt ssub_sat(const APInt &RHS) const;
   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.
   ///
   /// \returns the bit value at bitPosition
   bool operator[](unsigned bitPosition) const {
     assert(bitPosition < getBitWidth() && "Bit position out of bounds!");
     return (maskBit(bitPosition) & getWord(bitPosition)) != 0;
   }

llvm/lib/Support/APInt.cpp

APInt APInt::umul_sat(const APInt &RHS) const {
   bool Overflow;
   APInt Res = umul_ov(RHS, Overflow);
   if (!Overflow)
     return Res;
 
   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");
   assert((radix == 10 || radix == 8 || radix == 16 || radix == 2 ||
           radix == 36) &&
          "Radix should be 2, 8, 10, 16, or 36!");
 
   StringRef::iterator p = str.begin();

llvm/unittests/ADT/APIntTest.cpp

TEST(APIntTest, SaturatingMath) {
   EXPECT_EQ(APInt(8, -125), APInt(8, -25).smul_sat(APInt(8, 5)));
   EXPECT_EQ(APInt(8, -125), APInt(8, 25).smul_sat(APInt(8, -5)));
   EXPECT_EQ(APInt(8, 125), APInt(8, -25).smul_sat(APInt(8, -5)));
   EXPECT_EQ(APInt(8, 125), APInt(8, 25).smul_sat(APInt(8, 5)));
   EXPECT_EQ(APInt(8, -128), APInt(8, -25).smul_sat(APInt(8, 6)));
   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) {
   EXPECT_EQ(APInt(32, uint64_t(1)), APInt(32, ArrayRef<uint64_t>(1)));
 }
 
 TEST(APIntTest, StringBitsNeeded2) {
   EXPECT_EQ(1U, APInt::getBitsNeeded(  "0", 2));