Subzero: Improve the representation and handling of the FakeKill instruction.

src/IceTargetLoweringX8632.h

Index: src/IceTargetLoweringX8632.h
diff --git a/src/IceTargetLoweringX8632.h b/src/IceTargetLoweringX8632.h
index 7422f8a243916a9444cf78fe5564b41b609c17f6..985d3ae6a3e5c2cb6c5a0d0ddaa101e538ca28cb 100644
--- a/src/IceTargetLoweringX8632.h
+++ b/src/IceTargetLoweringX8632.h
@@ -484,10 +484,20 @@ protected:
   SizeT NextLabelNumber;
   bool ComputedLiveRanges;
   VarList PhysicalRegisters[IceType_NUM];
+  VarList FakeKilledScratchRegisters;
   static IceString RegNames[];
 
 private:
   ~TargetX8632() override {}
+  // Ideally, this initialization would be done in the constructor,
+  // but we need to defer it until after the initial CFG is built,
+  // because some of the bitcode reader tests rely on the order that
+  // Variables are created and their default printable names.
+  void initFakeKilledScratchRegisters() {
+    for (SizeT I = 0; I < ScratchRegs.size(); ++I)
+      if (ScratchRegs[I])
+        FakeKilledScratchRegisters.push_back(getPhysicalRegister(I));
+  }
   template <typename T> void emitConstantPool() const;
 };