[APInt] Rename getSignBit to getSignMask

getSignBit is a static function that creates an APInt with only the sign bit set. getSignMask seems like a better name to convey its functionality. In fact several places use it and then store in an APInt named SignMask.

Differential Revision: https://reviews.llvm.org/D32108

llvm-svn: 300856
diff --git a/llvm/lib/Transforms/Utils/CmpInstAnalysis.cpp b/llvm/lib/Transforms/Utils/CmpInstAnalysis.cpp
index 60ae374..9f4d9c7 100644
--- a/llvm/lib/Transforms/Utils/CmpInstAnalysis.cpp
+++ b/llvm/lib/Transforms/Utils/CmpInstAnalysis.cpp
@@ -73,17 +73,17 @@
   default:
     return false;
   case ICmpInst::ICMP_SLT:
-    // X < 0 is equivalent to (X & SignBit) != 0.
+    // X < 0 is equivalent to (X & SignMask) != 0.
     if (!C->isZero())
       return false;
-    Y = ConstantInt::get(I->getContext(), APInt::getSignBit(C->getBitWidth()));
+    Y = ConstantInt::get(I->getContext(), APInt::getSignMask(C->getBitWidth()));
     Pred = ICmpInst::ICMP_NE;
     break;
   case ICmpInst::ICMP_SGT:
-    // X > -1 is equivalent to (X & SignBit) == 0.
+    // X > -1 is equivalent to (X & SignMask) == 0.
     if (!C->isAllOnesValue())
       return false;
-    Y = ConstantInt::get(I->getContext(), APInt::getSignBit(C->getBitWidth()));
+    Y = ConstantInt::get(I->getContext(), APInt::getSignMask(C->getBitWidth()));
     Pred = ICmpInst::ICMP_EQ;
     break;
   case ICmpInst::ICMP_ULT: