[PATCH] Add support for generating MIPS legacy NaN

[Daniel Sanders]

LGTM with a couple tiny nits.


================
Comment at: include/clang/Basic/TargetInfo.h:642
@@ +641,3 @@
+  /// \brief Returns true if NaN encoding is IEEE 754-2008.
+  /// Only on MIPS can be different encoding.
+  virtual bool isNan2008() const {
----------------
Small nit: The grammar is a little odd, possibly a missing word? Maybe use 'Only MIPS allows a different encoding'

================
Comment at: lib/AST/ExprConstant.cpp:7599-7603
@@ +7598,7 @@
+  } else {
+    // Prior to IEEE 754-2008, architectures were allowed to choose the
+    // first bit of their significand set for qNaN and sNaN. MIPS chose
+    // different encoding to what became a standard in 2008, and for pre-
+    // 2008 revisions, MIPS interpreted sNaN-2008 as qNan and qNaN-2008 as
+    // sNaN. This is now known as "legacy NaN" encoding.
+    if (SNaN)
----------------
Just a couple tiny grammar nits:

"...to choose the first bit of their significand set for qNaN and sNaN." -> "...to choose whether the first bit of their significand was set for qNaN or sNaN."

"MIPS chose different encoding..." -> "MIPS chose a different encoding...".

http://reviews.llvm.org/D7882

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