[APInt] In sext single word case, use SignExtend64 and let the APInt constructor mask off any excess bits.

The current code is trying to be clever with shifts to avoid needing to clear unused bits. But it looks like the compiler is unable to optimize out the unused bit handling in the APInt constructor. Given this its better to just use SignExtend64 and have more readable code.

llvm-svn: 301133

2 files changed, 22 insertions, 5 deletions

diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index 9bb364af279..3f552db7963 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -942,11 +942,8 @@ APInt APInt::trunc(unsigned width) const {
 APInt APInt::sext(unsigned width) const {
   assert(width > BitWidth && "Invalid APInt SignExtend request");
 
-  if (width <= APINT_BITS_PER_WORD) {
-    uint64_t val = VAL << (APINT_BITS_PER_WORD - BitWidth);
-    val = (int64_t)val >> (width - BitWidth);
-    return APInt(width, val >> (APINT_BITS_PER_WORD - width));
-  }
+  if (width <= APINT_BITS_PER_WORD)
+    return APInt(width, SignExtend64(VAL, BitWidth));
 
   APInt Result(getMemory(getNumWords(width)), width);
 
diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
index 5d3afe9a159..1e20ebb320c 100644
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -2086,4 +2086,24 @@ TEST(APIntTest, isSubsetOf) {
   EXPECT_TRUE(i128_3.isSubsetOf(i128_3));
 }
 
+TEST(APIntTest, sext) {
+  EXPECT_EQ(0, APInt(1, 0).sext(64));
+  EXPECT_EQ(~uint64_t(0), APInt(1, 1).sext(64));
+
+  APInt i32_max(APInt::getSignedMaxValue(32).sext(63));
+  EXPECT_EQ(32U, i32_max.countLeadingZeros());
+  EXPECT_EQ(0U, i32_max.countTrailingZeros());
+  EXPECT_EQ(31U, i32_max.countPopulation());
+
+  APInt i32_min(APInt::getSignedMinValue(32).sext(63));
+  EXPECT_EQ(32U, i32_min.countLeadingOnes());
+  EXPECT_EQ(31U, i32_min.countTrailingZeros());
+  EXPECT_EQ(32U, i32_min.countPopulation());
+
+  APInt i32_neg1(APInt(32, ~uint64_t(0)).sext(63));
+  EXPECT_EQ(63U, i32_neg1.countLeadingOnes());
+  EXPECT_EQ(0U, i32_neg1.countTrailingZeros());
+  EXPECT_EQ(63U, i32_neg1.countPopulation());
+}
+
 } // end anonymous namespace