From: Craig Topper <craig.topper@gmail.com>
Date: Mon, 24 Apr 2017 05:38:26 +0000 (+0000)
Subject: [APInt] Make behavior of ashr by BitWidth consistent between single and multi word.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=6a61317c632e6dde307340bddba338832d47d997;p=llvm

[APInt] Make behavior of ashr by BitWidth consistent between single and multi word.

Previously single word would always return 0 regardless of the original sign. Multi word would return all 0s or all 1s based on the original sign. Now single word takes into account the sign as well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301159 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp
index 3f552db7963..e056f8ba853 100644
--- a/lib/Support/APInt.cpp
+++ b/lib/Support/APInt.cpp
@@ -1041,7 +1041,9 @@ APInt APInt::ashr(unsigned shiftAmt) const {
   // Handle single word shifts with built-in ashr
   if (isSingleWord()) {
     if (shiftAmt == BitWidth)
-      return APInt(BitWidth, 0); // undefined
+      // Undefined
+      return APInt(BitWidth,
+                   SignExtend64(VAL, BitWidth) >> (APINT_BITS_PER_WORD - 1));
     return APInt(BitWidth, SignExtend64(VAL, BitWidth) >> shiftAmt);
   }
 
diff --git a/unittests/ADT/APIntTest.cpp b/unittests/ADT/APIntTest.cpp
index 1e20ebb320c..e0a53a56455 100644
--- a/unittests/ADT/APIntTest.cpp
+++ b/unittests/ADT/APIntTest.cpp
@@ -288,7 +288,7 @@ TEST(APIntTest, i1) {
   EXPECT_EQ(zero, one.shl(1));
   EXPECT_EQ(one, one.shl(0));
   EXPECT_EQ(zero, one.lshr(1));
-  EXPECT_EQ(zero, one.ashr(1));
+  EXPECT_EQ(one, one.ashr(1));
 
   // Rotates.
   EXPECT_EQ(one, one.rotl(0));