ARM: Add a postRA pass to legalize stack offsets. Greedy approach (reserve IP).

src/IceTargetLoweringX86BaseImpl.h

Index: src/IceTargetLoweringX86BaseImpl.h
diff --git a/src/IceTargetLoweringX86BaseImpl.h b/src/IceTargetLoweringX86BaseImpl.h
index fc0a8e207a44a0a8a1b98baa6fb581c9259bd9c6..e33df3fd813da3d8388d84eb2d2cdaf427f2212f 100644
--- a/src/IceTargetLoweringX86BaseImpl.h
+++ b/src/IceTargetLoweringX86BaseImpl.h
@@ -756,12 +756,16 @@ void TargetX86Base<Machine>::emitVariable(const Variable *Var) const {
     llvm_unreachable("Infinite-weight Variable has no register assigned");
   }
   int32_t Offset = Var->getStackOffset();
-  if (!hasFramePointer())
-    Offset += getStackAdjustment();
+  int32_t BaseRegNum = Var->getBaseRegNum();

[jvoung (off chromium), 2015/07/23 23:26:32]

Well.. this is an extra virtual call, but I didn't have a good idea for
overriding if it happened to be something like StackVariable (though that's only
applicable for ARM). I didn't want to override "emit()" and "dump()" and do
something like override stackVarToAsmOperand(), since it's *almost* the same.

[Jim Stichnoth, 2015/07/24 22:08:29]

No need to worry about performance in dump() or emit() functions.

BTW, this being an emit() function, it should start with:
  if (!BuildDefs::dump())
    return;

[jvoung (off chromium), 2015/07/27 17:02:58]

Okay stackVarToAsmOperand also does this though, and it's used by emitIAS.
Added here, and in arm and mips.

+  if (BaseRegNum == Variable::NoRegister) {
+    BaseRegNum = getFrameOrStackReg();
+    if (!hasFramePointer())
+      Offset += getStackAdjustment();
+  }
   if (Offset)
     Str << Offset;
   const Type FrameSPTy = IceType_i32;
-  Str << "(%" << getRegName(getFrameOrStackReg(), FrameSPTy) << ")";
+  Str << "(%" << getRegName(BaseRegNum, FrameSPTy) << ")";
 }
 
 template <class Machine>
@@ -773,10 +777,14 @@ TargetX86Base<Machine>::stackVarToAsmOperand(const Variable *Var) const {
     llvm_unreachable("Infinite-weight Variable has no register assigned");
   }
   int32_t Offset = Var->getStackOffset();
-  if (!hasFramePointer())
-    Offset += getStackAdjustment();
+  int32_t BaseRegNum = Var->getBaseRegNum();
+  if (Var->getBaseRegNum() == Variable::NoRegister) {
+    BaseRegNum = getFrameOrStackReg();
+    if (!hasFramePointer())
+      Offset += getStackAdjustment();
+  }
   return typename Traits::Address(
-      Traits::RegisterSet::getEncodedGPR(getFrameOrStackReg()), Offset);
+      Traits::RegisterSet::getEncodedGPR(BaseRegNum), Offset);
 }
 
 template <class Machine> void TargetX86Base<Machine>::lowerArguments() {