Stop APInt::shl from generating llvm.trap

APInt::shl generated llvm.trap to guard against shifts greater than bit-width.
This was already checked with an assert, and there was a special case for
shifts equal to bit-width. Modify this check to catch shifts greater than or
equal to bit-width, so llvm.trap isn't generated.

Patch contributed by JF Bastien

llvm-svn: 166803

include/llvm/ADT/APInt.h

@@ -760,7 +760,7 @@ public:
   APInt shl(unsigned shiftAmt) const {
     assert(shiftAmt <= BitWidth && "Invalid shift amount");
     if (isSingleWord()) {
-      if (shiftAmt == BitWidth)
+      if (shiftAmt >= BitWidth)
         return APInt(BitWidth, 0); // avoid undefined shift results
       return APInt(BitWidth, VAL << shiftAmt);
     }