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
minetest · Dec 28, 2021 · cc64a04 · cc64a04
1 parent 7f6306c
commit cc64a04
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diff --git 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
@@ -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")