Enhance address mode recovery

src/IceAssemblerX86BaseImpl.h

 //===- subzero/src/IceAssemblerX86BaseImpl.h - base x86 assembler -*- C++ -*-=//
 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // Modified by the Subzero authors.
 //
 //===----------------------------------------------------------------------===//
 //
 //                        The Subzero Code Generator
@@ skipping 3295 matching lines @@
   }
   label->bindTo(bound);
 }
 
 template <class Machine>
 void AssemblerX86Base<Machine>::emitOperand(
     int rm, const typename Traits::Operand &operand) {
   assert(rm >= 0 && rm < 8);
   const intptr_t length = operand.length_;
   assert(length > 0);
+  intptr_t displacement_start = 1;
   // Emit the ModRM byte updated with the given RM value.
   assert((operand.encoding_[0] & 0x38) == 0);
   emitUint8(operand.encoding_[0] + (rm << 3));
+  // Whenever the addressing mode is not register indirect, using esp == 0x4
+  // as the register operation indicates an SIB byte follows.
+  if (((operand.encoding_[0] & 0xc0) != 0xc0) &&
+      ((operand.encoding_[0] & 0x07) == 0x04)) {
+    emitUint8(operand.encoding_[1]);
+    displacement_start = 2;
+  }
+  // Emit the displacement and the fixup that affects it, if any.
   if (operand.fixup()) {
     emitFixup(operand.fixup());
+    assert(length - displacement_start == 4);
   }
-  // Emit the rest of the encoded operand.
-  for (intptr_t i = 1; i < length; i++) {
+  for (intptr_t i = displacement_start; i < length; i++) {
     emitUint8(operand.encoding_[i]);
   }
 }
 
 template <class Machine>
 void AssemblerX86Base<Machine>::emitImmediate(Type Ty, const Immediate &imm) {
   if (Ty == IceType_i16) {
     assert(!imm.fixup());
     emitInt16(imm.value());
   } else {
@@ skipping 103 matching lines @@
   (void)shifter;
   if (Ty == IceType_i16)
     emitOperandSizeOverride();
   emitRexB(Ty, operand.rm());
   emitUint8(isByteSizedArithType(Ty) ? 0xD2 : 0xD3);
   emitOperand(rm, operand);
 }
 
 } // end of namespace X86Internal
 } // end of namespace Ice