Introduction of improved switch lowering.

src/IceTargetLoweringX86Base.h

Index: src/IceTargetLoweringX86Base.h
diff --git a/src/IceTargetLoweringX86Base.h b/src/IceTargetLoweringX86Base.h
index c00f0b0e5524207dec9ccf1275de84f6ced074e4..e2aacb74fb1e09e3ffa12ae9cb24d8400ec5ce91 100644
--- a/src/IceTargetLoweringX86Base.h
+++ b/src/IceTargetLoweringX86Base.h
@@ -19,6 +19,7 @@
 
 #include "IceDefs.h"
 #include "IceInst.h"
+#include "IceSwitchLowering.h"
 #include "IceTargetLowering.h"
 
 #include <type_traits>
@@ -130,6 +131,8 @@ public:
     return (typeWidthInBytes(Ty) + 3) & ~3;
   }
 
+  SizeT getMinJumpTableSize() const override { return 4; }
+
   void emitVariable(const Variable *Var) const override;
 
   const char *getConstantPrefix() const final { return "$"; }
@@ -203,6 +206,16 @@ protected:
   void lowerCountZeros(bool Cttz, Type Ty, Variable *Dest, Operand *FirstVal,
                        Operand *SecondVal);
 
+  /// Check the comparison is in [Min,Max]. If not in the range, above will be
+  /// set, if in the range below equal will be set. The index into the range is

[jvoung (off chromium), 2015/07/15 18:32:01]

For "above will be set" and "below equal will be..." I think it would be good to
clarify that you mean the x86 flags register (due to insert cmp instructions).

[ascull, 2015/07/16 19:38:45]

Done.

+  /// returned.
+  Operand *lowerCmpRange(Operand *Comparison, uint64_t Min, uint64_t Max);
+  /// Lowering of a cluster of switch cases. If the case is not matched control
+  /// will pass to the default label provided. If the default label is nullptr
+  /// then control will fall through to the next instruction.
+  void lowerCaseCluster(const CaseCluster &Case, Operand *Src0,
+                        CfgNode *DefaultLabel=nullptr);
+
   typedef void (TargetX86Base::*LowerBinOp)(Variable *, Operand *);
   void expandAtomicRMWAsCmpxchg(LowerBinOp op_lo, LowerBinOp op_hi,
                                 Variable *Dest, Operand *Ptr, Operand *Val);