Fix llvm::huge_valf multiple initializations with Visual C++.

llvm::huge_valf is defined in a header file, so it is initialized
multiple times in every compiled unit upon program startup.

With non-VC compilers huge_valf is set to a HUGE_VALF which the
compiler can probably optimize out.

With VC numeric_limits<float>::infinity() does not return a number
but a runtime structure member which therotically may change 
between calls so the compiler does not optimize out the 
initialization and it happens many times. It can be easily seen by 
placing a breakpoint on the initialization line.

This patch moves llvm::huge_valf initialization to a source file
instead of the header.

llvm-svn: 218567

1 files changed, 32 insertions, 0 deletions

diff --git a/llvm/lib/Support/MathExtras.cpp b/llvm/lib/Support/MathExtras.cpp
new file mode 100644
index 00000000000..ba0924540ce
--- /dev/null
+++ b/llvm/lib/Support/MathExtras.cpp
@@ -0,0 +1,32 @@
+//===-- MathExtras.cpp - Implement the MathExtras header --------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the MathExtras.h header
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/MathExtras.h"
+
+#ifdef _MSC_VER
+#include <limits>
+#else
+#include <math.h>
+#endif
+
+namespace llvm {
+
+#if defined(_MSC_VER)
+  // Visual Studio defines the HUGE_VAL class of macros using purposeful
+  // constant arithmetic overflow, which it then warns on when encountered.
+  const float huge_valf = std::numeric_limits<float>::infinity();
+#else
+  const float huge_valf = HUGE_VALF;
+#endif
+
+}