Subzero: Fix JumpTable lowering on x86-64.

src/IceTargetLoweringX86BaseImpl.h

 //===- subzero/src/IceTargetLoweringX86BaseImpl.h - x86 lowering -*- C++ -*-==//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 5835 matching lines @@
     }
 
     InstJumpTable *JumpTable = Case.getJumpTable();
     Context.insert(JumpTable);
 
     // Make sure the index is a register of the same width as the base
     Variable *Index;
     const Type PointerType = getPointerType();
     if (RangeIndex->getType() != PointerType) {
       Index = makeReg(PointerType);
-      _movzx(Index, RangeIndex);
+      if (RangeIndex->getType() == IceType_i64) {

[John, 2016/02/29 15:34:09]

How do you feel about:

if (typeSizeInByes(PointerType) > typSizeInBytes(RangeIndex.getType()) {
  Index = makeReg(PointerType);
  _movzx(Index, RangeIndex);
} else if (typeSizeInByes(PointerType) < typSizeInBytes(RangeIndex.getType()) {
  Index = makeReg(PointerType);
  _mov(Index, RangeIndex);
} else {
  Index = legalizeToReg(RangeIndex);
}

This is "moar" future-proof should we ever need a non-ILP32 target.

+        assert(Traits::Is64Bit);
+        _mov(Index, RangeIndex); // trunc
+      } else {
+        _movzx(Index, RangeIndex);
+      }
     } else {
       Index = legalizeToReg(RangeIndex);
     }
 
     constexpr RelocOffsetT RelocOffset = 0;
     constexpr bool SuppressMangling = true;
     IceString MangledName = Ctx->mangleName(Func->getFunctionName());
     constexpr Variable *NoBase = nullptr;
     Constant *Offset = Ctx->getConstantSym(
         RelocOffset, InstJumpTable::makeName(MangledName, JumpTable->getId()),
@@ skipping 1536 matching lines @@
         emitGlobal(*Var, SectionSuffix);
       }
     }
   } break;
   }
 }
 } // end of namespace X86NAMESPACE
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETARGETLOWERINGX86BASEIMPL_H