[SubZero] Implement load and store for MIPS

src/IceTargetLoweringMIPS32.h

Index: src/IceTargetLoweringMIPS32.h
diff --git a/src/IceTargetLoweringMIPS32.h b/src/IceTargetLoweringMIPS32.h
index 5d5a98ec9966cb315e4c7503c5e15d988ecbe08b..b555b9bcf6ae62b5afca1f6b00bc24b3921b5350 100644
--- a/src/IceTargetLoweringMIPS32.h
+++ b/src/IceTargetLoweringMIPS32.h
@@ -101,9 +101,7 @@ public:
     PrologEmitsFixedAllocas = true;
   }
   int32_t getFrameFixedAllocaOffset() const override {
-    // TODO(sehr): Implement fixed stack layout.
-    llvm::report_fatal_error("Not yet implemented");
-    return 0;
+    return FixedAllocaSizeBytes - (SpillAreaSizeBytes - MaxOutArgsSizeBytes);
   }
 
   uint32_t maxOutArgsSizeBytes() const override { return MaxOutArgsSizeBytes; }
@@ -448,6 +446,7 @@ public:
     Legal_Reg = 1 << 0, // physical register, not stack location
     Legal_Imm = 1 << 1,
     Legal_Mem = 1 << 2,
+    Legal_Rematerializable = 1 << 3,
     Legal_Default = ~Legal_None
   };
   typedef uint32_t LegalMask;