[APInt] In sext single word case, use SignExtend64 and let the APInt constructor...

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

diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index 9bb364a..3f552db 100644 (file)
--- 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 5d3afe9..1e20ebb 100644 (file)
--- 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