[llvm] r174641 - ADT: Correct APInt::getActiveWords for zero values

[Meador Inge]

Author: meadori
Date: Thu Feb  7 12:36:50 2013
New Revision: 174641

URL: http://llvm.org/viewvc/llvm-project?rev=174641&view=rev
Log:
ADT: Correct APInt::getActiveWords for zero values

PR15138 was opened because of a segfault in the Bitcode writer.
The actual issue ended up being a bug in APInt where calls to
APInt::getActiveWords returns a bogus value when the APInt value
is 0.  This patch fixes the problem by ensuring that getActiveWords
returns 1 for 0 valued APInts.

Modified:
    llvm/trunk/include/llvm/ADT/APInt.h
    llvm/trunk/unittests/ADT/APIntTest.cpp

Modified: llvm/trunk/include/llvm/ADT/APInt.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/APInt.h?rev=174641&r1=174640&r2=174641&view=diff
==============================================================================
--- llvm/trunk/include/llvm/ADT/APInt.h (original)
+++ llvm/trunk/include/llvm/ADT/APInt.h Thu Feb  7 12:36:50 2013
@@ -1191,7 +1191,8 @@ public:
   /// APInt. This is used in conjunction with getActiveData to extract the raw
   /// value of the APInt.
   unsigned getActiveWords() const {
-    return whichWord(getActiveBits()-1) + 1;
+    unsigned numActiveBits = getActiveBits();
+    return numActiveBits ? whichWord(numActiveBits - 1) + 1 : 1;
   }
 
   /// Computes the minimum bit width for this APInt while considering it to be

Modified: llvm/trunk/unittests/ADT/APIntTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/ADT/APIntTest.cpp?rev=174641&r1=174640&r2=174641&view=diff
==============================================================================
--- llvm/trunk/unittests/ADT/APIntTest.cpp (original)
+++ llvm/trunk/unittests/ADT/APIntTest.cpp Thu Feb  7 12:36:50 2013
@@ -56,6 +56,14 @@ TEST(APIntTest, i33_Count) {
 #endif
 
 TEST(APIntTest, i65_Count) {
+  APInt i65(65, 0, true);
+  EXPECT_EQ(65u, i65.countLeadingZeros());
+  EXPECT_EQ(0u, i65.countLeadingOnes());
+  EXPECT_EQ(0u, i65.getActiveBits());
+  EXPECT_EQ(1u, i65.getActiveWords());
+  EXPECT_EQ(65u, i65.countTrailingZeros());
+  EXPECT_EQ(0u, i65.countPopulation());
+
   APInt i65minus(65, 0, true);
   i65minus.setBit(64);
   EXPECT_EQ(0u, i65minus.countLeadingZeros());