Add a target lowering hook to control whether it's worthwhile to compress fp constant.

For x86, if sse2 is available, it's not a good idea since cvtss2sd is slower than a movsd load and it prevents load folding. On x87, it's important to shrink fp constant since fldt is very expensive.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47931 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetLowering.h

@@ -467,6 +467,11 @@ public:
     assert(0 && "Unsupported extended type!");
   }
 
+  /// ShouldShrinkFPConstant - If true, then instruction selection should
+  /// seek to shrink the FP constant of the specified type to a smaller type
+  /// in order to save space and / or reduce runtime.
+  virtual bool ShouldShrinkFPConstant(MVT::ValueType VT) const { return true; }
+
   /// hasTargetDAGCombine - If true, the target has custom DAG combine
   /// transformations that it can perform for the specified node.
   bool hasTargetDAGCombine(ISD::NodeType NT) const {