[Mesa-dev] [PATCH] glsl: use -O0 optimization for builtin_functions.cpp with MinGW

[Brian Paul]

Some versions of MinGW-w64 such as 5.3.1 and 6.2.0 produce bad code
with -O2 or -O3 causing a random driver crash when running programs
that use GLSL.  Most Mesa demos in the glsl/ directory trigger the
bug, but not the fragcoord.c test.

Use a #pragma to force -O1 for this file for later MinGW versions.
Luckily, this is basically one-time setup code.  I suspect the bug
is related to the sheer size of this file.

This should let us move to newer versions of MinGW-w64 for Mesa.
---
 src/compiler/glsl/builtin_functions.cpp | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/compiler/glsl/builtin_functions.cpp b/src/compiler/glsl/builtin_functions.cpp
index e30509a..e32b18c 100644
--- a/src/compiler/glsl/builtin_functions.cpp
+++ b/src/compiler/glsl/builtin_functions.cpp
@@ -53,6 +53,26 @@
  *    name and parameters.
  */
 
+
+/**
+ * Unfortunately, some versions of MinGW produce bad code if this file
+ * is compiled with -O2 or -O3.  The resulting driver will crash in random
+ * places if the app uses GLSL.
+ * The work-around is to disable optimizations for just this file.  Luckily,
+ * this code is basically just executed once.
+ *
+ * MinGW 4.6.3 (in Ubuntu 13.10) does not have this bug.
+ * MinGW 5.3.1 (in Ubuntu 16.04) definitely has this bug.
+ * MinGW 6.2.0 (in Ubuntu 16.10) definitely has this bug.
+ * MinGW x.y.z - don't know.  Assume versions after 4.6.x are buggy
+ */
+
+#if defined(__MINGW32__) && ((__GNUC__ * 100) + __GNUC_MINOR >= 407)
+#warning "disabling optimizations for this file to work around compiler bug"
+#pragma GCC optimize("O0")
+#endif
+
+
 #include <stdarg.h>
 #include <stdio.h>
 #include "main/core.h" /* for struct gl_shader */
-- 
1.9.1