build: target x86-64-v3 without floating-point contraction

CMakeLists.txt

@@ -407,6 +407,8 @@ add_executable(scalar_provenance_tests EXCLUDE_FROM_ALL
 target_link_libraries(scalar_provenance_tests fmt::fmt xbyak::xbyak)
 target_include_directories(scalar_provenance_tests PRIVATE ${inc_headers})
 
+add_executable(build_flags_tests EXCLUDE_FROM_ALL "${KYTY_TESTS_DIR}/BuildFlagsTests.cpp")
+
 add_executable(page_manager_tests EXCLUDE_FROM_ALL
 	"${KYTY_TESTS_DIR}/PageManagerTests.cpp"
 	"${KYTY_SOURCE_DIR}/graphics/host_gpu/pageManager.cpp"
@@ -650,6 +652,7 @@ if(BUILD_TESTING)
 	add_test(NAME image_page_table COMMAND $<TARGET_FILE:image_page_table_tests>)
 	add_test(NAME memory_tracker COMMAND $<TARGET_FILE:memory_tracker_tests>)
 	add_test(NAME page_manager COMMAND $<TARGET_FILE:page_manager_tests>)
+	add_test(NAME build_flags COMMAND $<TARGET_FILE:build_flags_tests>)
 	add_test(NAME archive_file COMMAND $<TARGET_FILE:archive_file_tests>)
 	add_test(NAME trophy_system COMMAND $<TARGET_FILE:trophy_system_tests>)
 	add_test(NAME avplayer_file COMMAND $<TARGET_FILE:avplayer_file_tests>)
@@ -743,6 +746,7 @@ if(BUILD_TESTING)
 		image_page_table_tests
 		memory_tracker_tests
 		page_manager_tests
+		build_flags_tests
 		archive_file_tests
 		trophy_system_tests
 		avplayer_file_tests

src/utils.cmake

@@ -65,6 +65,8 @@ else()
 	SET(CMAKE_NINJA_FORCE_RESPONSE_FILE 1 CACHE INTERNAL "")
 endif()
 
+# Guest code runs natively and needs x86-64-v3 (AVX2, BMI2, FMA), so every host has it.
+# No FMA contraction: a * b + c keeps both roundings.
 if(KYTY_CLANG_CL)
 	if(CMAKE_CXX_FLAGS MATCHES "/W[0-4]")
 		string(REGEX REPLACE "/W[0-4]" "/W3" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
@@ -79,7 +81,7 @@ if(KYTY_CLANG_CL)
 	string(REGEX REPLACE "/MD" "/MT" CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE}")
 	string(REGEX REPLACE "/MD" "/MT" CMAKE_C_FLAGS "${CMAKE_C_FLAGS}")
 			
-	set(KYTY_CPP_FLAGS "${KYTY_CPP_FLAGS} /utf-8 /Oy- /wd4244 /wd4305 /wd4800 /wd4345")
+	set(KYTY_CPP_FLAGS "${KYTY_CPP_FLAGS} /utf-8 /Oy- /clang:-march=x86-64-v3 /clang:-ffp-contract=off /wd4244 /wd4305 /wd4800 /wd4345")
   
 	if(KYTY_WARNINGS_ARE_ERRORS)
 		#set(KYTY_CPP_FLAGS "${KYTY_CPP_FLAGS} /WX")
@@ -103,6 +105,7 @@ elseif(CLANG OR GCC)
 	else()
 		set(KYTY_CPP_FLAGS "${KYTY_CPP_FLAGS} -fno-exceptions -fdiagnostics-color=always -finput-charset=UTF-8 -fexec-charset=UTF-8 -static-libgcc -static-libstdc++ -g -fno-strict-aliasing -fno-omit-frame-pointer -Wall -Wno-unused-value -fmessage-length=0")
 	endif()
+	set(KYTY_CPP_FLAGS "${KYTY_CPP_FLAGS} -march=x86-64-v3 -ffp-contract=off")
 	
     if(KYTY_WARNINGS_ARE_ERRORS)
         #set(KYTY_CPP_FLAGS "${KYTY_CPP_FLAGS} -Werror")

tests/BuildFlagsTests.cpp

@@ -0,0 +1,17 @@
+#include <cstdio>
+
+#if !defined(__AVX2__) || !defined(__BMI2__) || !defined(__FMA__)
+#error "x86-64 builds target x86-64-v3"
+#endif
+
+int main() {
+  // (1 + 2^-23)^2 = 1 + 2^-22 + 2^-46; only a fused multiply-add keeps the 2^-46.
+  volatile float a = 1.0f + 0x1p-23f;
+  const float result = a * a - (1.0f + 0x1p-22f);
+  if (result != 0.0f) {
+    std::fprintf(stderr, "BuildFlagsTests: failed: a * a - b was contracted (%a)\n", result);
+    return 1;
+  }
+  std::puts("BuildFlagsTests: all cases passed");
+  return 0;
+}