Subzero: Fix sign issues for inlined memset lowering.

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 4962 matching lines @@
   // Unlikely, but nothing to do if it does happen
   if (IsCountConst && CountValue == 0)
     return;
 
   // TODO(ascull): if the count is constant but val is not it would be possible
   // to inline by spreading the value across 4 bytes and accessing subregs e.g.
   // eax, ax and al.
   if (shouldOptimizeMemIntrins() && IsCountConst && IsValConst) {
     Variable *Base = nullptr;
     Variable *VecReg = nullptr;
+    const uint32_t MaskValue = (ValValue & 0xff);
     const uint32_t SpreadValue =
-        (ValValue << 24) | (ValValue << 16) | (ValValue << 8) | ValValue;
+        (MaskValue << 24) | (MaskValue << 16) | (MaskValue << 8) | MaskValue;
 
     auto lowerSet = [this, &Base, SpreadValue, &VecReg](Type Ty,
                                                         uint32_t OffsetAmt) {
       assert(Base != nullptr);
       Constant *Offset = OffsetAmt ? Ctx->getConstantInt32(OffsetAmt) : nullptr;
 
       // TODO(ascull): is 64-bit better with vector or scalar movq?
       auto *Mem = X86OperandMem::create(Func, Ty, Base, Offset);
       if (isVectorType(Ty)) {
         assert(VecReg != nullptr);
@@ skipping 3088 matching lines @@
         emitGlobal(*Var, SectionSuffix);
       }
     }
   } break;
   }
 }
 } // end of namespace X86NAMESPACE
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETARGETLOWERINGX86BASEIMPL_H