Automatically use SSE registers for FP operations on i386 (#11853)

use SSE for floating-point operations to avoid issues with improper fp-rounding and
loss of precision when moving fp-data to incompatible or less-precise
registers/storage locations

https://gcc.gnu.org/wiki/FloatingPointMath
https://gcc.gnu.org/wiki/x87note

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ea212bede0aea89dda943c4c724d771b441a487d..3b4b9f4f50e3cc9800bfc89303acf556c3a24c8d 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -286,7 +286,6 @@ endif()
 
 # Subdirectories
 # Be sure to add all relevant definitions above this
-
 add_subdirectory(src)
 
 

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 4803b475bfc9d0499c404addb9d8b3f1851fbbb6..e3389cea922a05ae65127a7a66aa5f0248f624cd 100644 (file)
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -769,6 +769,16 @@ else()
        # - 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")
 
+       # Enable SSE for floating point math on 32-bit x86 by default
+       # reasoning see minetest issue #11810 and https://gcc.gnu.org/wiki/FloatingPointMath
+       if(CMAKE_SIZEOF_VOID_P EQUAL 4)
+               check_c_source_compiles("#ifndef __i686__\n#error\n#endif\nint main(){}" IS_I686)
+               if(IS_I686)
+                       message(STATUS "Detected Intel x86: using SSE instead of x87 FPU")
+                       set(OTHER_FLAGS "${OTHER_FLAGS} -mfpmath=sse -msse")
+               endif()
+       endif()
+
        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")