Don't use -ffast-math or other unsafe math optimizations

Godot supports many different compilers and for production releases we have to support 3 currently: GCC8, Clang6, and MSVC2017. These compilers all do slightly different things with -ffast-math and it is causing issues now. See #24841, #24540, #10758, #10070. And probably other complaints about physics differences between release and release_debug builds. I've done some performance comparisons on Linux x86_64. All tests are ran 20 times. Bunnymark: (higher is better) (bunnies) min max stdev average fast-math 7332 7597 71 7432 this pr 7379 7779 108 7621 (102%) FPBench (gdscript port http://fpbench.org/) (lower is better) (ms) fast-math 15441 16127 192 15764 this pr 15671 16855 326 16001 (99%) Float_add (adding floats in a tight loop) (lower is better) (sec) fast-math 5.49 5.78 0.07 5.65 this pr 5.65 5.90 0.06 5.76 (98%) Float_div (dividing floats in a tight loop) (lower is better) (sec) fast-math 11.70 12.36 0.18 11.99 this pr 11.92 12.32 0.12 12.12 (99%) Float_mul (multiplying floats in a tight loop) (lower is better) (sec) fast-math 11.72 12.17 0.12 11.93 this pr 12.01 12.62 0.17 12.26 (97%) I have also looked at FPS numbers for tps-demo, 3d platformer, 2d platformer, and sponza and could not find any measurable difference. I believe that given the issues and oft-reported (physics) glitches on release builds I believe that the couple of percent of tight-loop floating point performance regression is well worth it. This fixes #24540 and fixes #24841

Don't use -ffast-math or other unsafe math optimizations
e5b335d3 · Hein-Pieter van Braam · e46f28e0 · e5b335d3 · e5b335d3 · e5b335d3
Commit e5b335d3 authored Jan 09, 2019 by Hein-Pieter van Braam
7 changed files
--- a/modules/etc/SCsub
+++ b/modules/etc/SCsub
@@ -33,11 +33,6 @@ env_etc.Append(CPPPATH=[thirdparty_dir])
 if not env.msvc:
 	env_etc.Append(CCFLAGS="-std=c++11")

-# -ffast-math seems to be incompatible with etc2comp on recent versions of
-# GCC and Clang
-if '-ffast-math' in env_etc['CCFLAGS']:
-	env_etc['CCFLAGS'].remove('-ffast-math')
-
 env_thirdparty = env_etc.Clone()
 env_thirdparty.disable_warnings()
 env_thirdparty.add_source_files(env.modules_sources, thirdparty_sources)

--- a/platform/android/detect.py
+++ b/platform/android/detect.py
@@ -141,7 +141,7 @@ def configure(env):
    if (env["target"].startswith("release")):
        if (env["optimize"] == "speed"): #optimize for speed (default)
            env.Append(LINKFLAGS=['-O2'])
-            env.Append(CPPFLAGS=['-O2', '-DNDEBUG', '-ffast-math', '-funsafe-math-optimizations', '-fomit-frame-pointer'])
+            env.Append(CPPFLAGS=['-O2', '-DNDEBUG', '-fomit-frame-pointer'])
        else: #optimize for size
            env.Append(CPPFLAGS=['-Os', '-DNDEBUG'])
            env.Append(LINKFLAGS=['-Os'])

--- a/platform/haiku/detect.py
+++ b/platform/haiku/detect.py
@@ -37,14 +37,14 @@ def configure(env):
    ## Build type

    if (env["target"] == "release"):
-        env.Prepend(CCFLAGS=['-O3', '-ffast-math'])
+        env.Prepend(CCFLAGS=['-O3'])
        if (env["debug_symbols"] == "yes"):
            env.Prepend(CCFLAGS=['-g1'])
        if (env["debug_symbols"] == "full"):
            env.Prepend(CCFLAGS=['-g2'])

    elif (env["target"] == "release_debug"):
-        env.Prepend(CCFLAGS=['-O2', '-ffast-math', '-DDEBUG_ENABLED'])
+        env.Prepend(CCFLAGS=['-O2', '-DDEBUG_ENABLED'])
        if (env["debug_symbols"] == "yes"):
            env.Prepend(CCFLAGS=['-g1'])
        if (env["debug_symbols"] == "full"):

--- a/platform/iphone/detect.py
+++ b/platform/iphone/detect.py
@@ -46,7 +46,7 @@ def configure(env):
    if (env["target"].startswith("release")):
        env.Append(CPPFLAGS=['-DNDEBUG', '-DNS_BLOCK_ASSERTIONS=1'])
        if (env["optimize"] == "speed"): #optimize for speed (default)
-            env.Append(CPPFLAGS=['-O2', '-ftree-vectorize', '-fomit-frame-pointer', '-ffast-math', '-funsafe-math-optimizations'])
+            env.Append(CPPFLAGS=['-O2', '-ftree-vectorize', '-fomit-frame-pointer'])
            env.Append(LINKFLAGS=['-O2'])
        else: #optimize for size
            env.Append(CPPFLAGS=['-Os', '-ftree-vectorize'])

--- a/platform/osx/detect.py
+++ b/platform/osx/detect.py
@@ -42,7 +42,7 @@ def configure(env):

    if (env["target"] == "release"):
        if (env["optimize"] == "speed"): #optimize for speed (default)
-            env.Prepend(CCFLAGS=['-O3', '-ffast-math', '-fomit-frame-pointer', '-ftree-vectorize', '-msse2'])
+            env.Prepend(CCFLAGS=['-O3', '-fomit-frame-pointer', '-ftree-vectorize', '-msse2'])
        else: #optimize for size
            env.Prepend(CCFLAGS=['-Os','-ftree-vectorize', '-msse2'])


--- a/platform/server/detect.py
+++ b/platform/server/detect.py
@@ -43,10 +43,10 @@ def configure(env):
    ## Build type

    if (env["target"] == "release"):
-        env.Append(CCFLAGS=['-O2', '-ffast-math', '-fomit-frame-pointer'])
+        env.Append(CCFLAGS=['-O2', '-fomit-frame-pointer'])

    elif (env["target"] == "release_debug"):
-        env.Append(CCFLAGS=['-O2', '-ffast-math', '-DDEBUG_ENABLED'])
+        env.Append(CCFLAGS=['-O2', '-DDEBUG_ENABLED'])

    elif (env["target"] == "debug"):
        env.Append(CCFLAGS=['-g2', '-DDEBUG_ENABLED', '-DDEBUG_MEMORY_ENABLED'])

--- a/platform/x11/detect.py
+++ b/platform/x11/detect.py
@@ -86,10 +86,8 @@ def configure(env):
    ## Build type

    if (env["target"] == "release"):
-        # -O3 -ffast-math is identical to -Ofast. We need to split it out so we can selectively disable
-        # -ffast-math in code for which it generates wrong results.
        if (env["optimize"] == "speed"): #optimize for speed (default)
-            env.Prepend(CCFLAGS=['-O3', '-ffast-math'])
+            env.Prepend(CCFLAGS=['-O3'])
        else: #optimize for size
            env.Prepend(CCFLAGS=['-Os'])

@@ -100,7 +98,7 @@ def configure(env):

    elif (env["target"] == "release_debug"):
        if (env["optimize"] == "speed"): #optimize for speed (default)
-            env.Prepend(CCFLAGS=['-O2', '-ffast-math', '-DDEBUG_ENABLED'])
+            env.Prepend(CCFLAGS=['-O2', '-DDEBUG_ENABLED'])
        else: #optimize for size
            env.Prepend(CCFLAGS=['-Os', '-DDEBUG_ENABLED'])