[PATCH] Add support for generating MIPS legacy NaN

[Daniel Sanders]

================
Comment at: lib/AST/ExprConstant.cpp:7599-7603
@@ +7598,7 @@
+  } else {
+    // This case will be triggered for Mips legacy encoding.
+    if (SNaN)
+      Result = llvm::APFloat::getQNaN(Sem, false, &fill);
+    else
+      Result = llvm::APFloat::getSNaN(Sem, false, &fill);
+  }
----------------
Could you add a comment explaining the relevant history and why that leads to QNaN and SNaN being reversed here. It won't be obvious to most readers.

================
Comment at: lib/Basic/Targets.cpp:5679
@@ +5678,3 @@
+  bool isNan2008() const override {
+    return IsNan2008 || isNaN2008Default();
+  }
----------------
This isn't quite right. It should just be IsNan2008 since IsNan2008 is initialized with the result of isNaN2008Default().

================
Comment at: test/CodeGen/builtin-nan-legacy.c:2-3
@@ +1,4 @@
+// RUN: %clang -target mipsel-unknown-linux -mnan=legacy -emit-llvm -S -o %t %s
+// RUN: grep 'float 0x7FF4000000000000, float 0x7FF8000000000000' %t
+// RUN: grep 'double 0x7FF4000000000000, double 0x7FF8000000000000' %t
+
----------------
New tests should be using FileCheck rather than grep.

http://reviews.llvm.org/D7882

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