Swap out -ffast-math for a safe subset of optimization flags (#9682)

It caused more trouble than its worth.
fixes #3943, fixes #5330

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index fa261547bb12e77f898f03310aff801b0c2db6bb..d5f774d778c96ef7e02485681651017309132b42 100644 (file)
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -713,6 +713,11 @@ else()
                set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DWIN32_LEAN_AND_MEAN")
        endif()
 
+       # Use a safe subset of flags to speed up math calculations:
+       # - we don't need errno or math exceptions
+       # - we don't deal with Inf/NaN or signed zero
+       set(MATH_FLAGS "-fno-math-errno -fno-trapping-math -ffinite-math-only -fno-signed-zeros")
+
        set(CMAKE_CXX_FLAGS_RELEASE "-DNDEBUG ${RELEASE_WARNING_FLAGS} ${WARNING_FLAGS} ${OTHER_FLAGS} -Wall -pipe -funroll-loops")
        if(CMAKE_SYSTEM_NAME MATCHES "(Darwin|BSD|DragonFly)")
                set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -Os")
@@ -723,7 +728,7 @@ else()
                                AND CMAKE_CXX_COMPILER_VERSION MATCHES "^9\\.")
                        # Clang 9 has broken -ffast-math on glibc
                else()
-                       set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -ffast-math")
+                       set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} ${MATH_FLAGS}")
                endif()
        endif(CMAKE_SYSTEM_NAME MATCHES "(Darwin|BSD|DragonFly)")
        set(CMAKE_CXX_FLAGS_SEMIDEBUG "-g -O1 -Wall -Wabi ${WARNING_FLAGS} ${OTHER_FLAGS}")

diff --git a/src/collision.cpp b/src/collision.cpp
index 6d24bc699f10fe19acf6d7411b9cedb381a63dad..a089f33774d3bb66037b940c454c11ca06527666 100644 (file)
--- a/src/collision.cpp
+++ b/src/collision.cpp
@@ -32,6 +32,9 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "util/timetaker.h"
 #include "profiler.h"
 
+#ifdef __FAST_MATH__
+#warning "-ffast-math is known to cause bugs in collision code, do not use!"
+#endif
 
 struct NearbyCollisionInfo {
        NearbyCollisionInfo(bool is_ul, bool is_obj, int bouncy,