make ConstantRange::signExtend() optimal

the case [x, INT_MIN) was not handled optimally

llvm-svn: 193694

2 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Support/ConstantRange.cpp b/llvm/lib/Support/ConstantRange.cpp
index 1085a45d0a2..e3b43ed6df6 100644
--- a/llvm/lib/Support/ConstantRange.cpp
+++ b/llvm/lib/Support/ConstantRange.cpp
@@ -445,6 +445,11 @@ ConstantRange ConstantRange::signExtend(uint32_t DstTySize) const {
 
   unsigned SrcTySize = getBitWidth();
   assert(SrcTySize < DstTySize && "Not a value extension");
+
+  // special case: [X, INT_MIN) -- not really wrapping around
+  if (Upper == APInt::getHighBitsSet(SrcTySize, 1))
+    return ConstantRange(Lower.sext(DstTySize), Upper.zext(DstTySize));
+
   if (isFullSet() || isSignWrappedSet()) {
     return ConstantRange(APInt::getHighBitsSet(DstTySize,DstTySize-SrcTySize+1),
                          APInt::getLowBitsSet(DstTySize, SrcTySize-1) + 1);
diff --git a/llvm/unittests/Support/ConstantRangeTest.cpp b/llvm/unittests/Support/ConstantRangeTest.cpp
index 4d6bbf6f840..3e0a085ed1e 100644
--- a/llvm/unittests/Support/ConstantRangeTest.cpp
+++ b/llvm/unittests/Support/ConstantRangeTest.cpp
@@ -216,6 +216,9 @@ TEST_F(ConstantRangeTest, SExt) {
 
   EXPECT_EQ(ConstantRange(APInt(8, 120), APInt(8, 140)).signExtend(16),
             ConstantRange(APInt(16, -128), APInt(16, 128)));
+
+  EXPECT_EQ(ConstantRange(APInt(16, 0x0200), APInt(16, 0x8000)).signExtend(19),
+            ConstantRange(APInt(19, 0x0200), APInt(19, 0x8000)));
 }
 
 TEST_F(ConstantRangeTest, IntersectWith) {