Cycles: disable fast math flags, only use a subset.

Empty BVH nodes are set to NaN which must be preserved all the way to the
tnear <= tfar test which can then give false for empty nodes. This needs
strict semantices and careful argument ordering for min() and max(), so
the second argument is used if either of the arguments is NaN.

Fixes T52635: crash in BVH traversal with SSE4.1.

Differential Revision: https://developer.blender.org/D2828

1 files changed, 45 insertions, 41 deletions

diff --git a/intern/cycles/CMakeLists.txt b/intern/cycles/CMakeLists.txt
index c53a9f91cc0..5844c2480d6 100644
--- a/intern/cycles/CMakeLists.txt
+++ b/intern/cycles/CMakeLists.txt
@@ -41,61 +41,65 @@ elseif(WIN32 AND MSVC)
 		set(CYCLES_AVX2_ARCH_FLAGS "/arch:SSE2")
 	endif()
 
+	# Unlike GCC/clang we still use fast math, because there is no fine
+	# grained control and the speedup we get here is too big to ignore.
+	set(CYCLES_KERNEL_FLAGS "/fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
+
 	# there is no /arch:SSE3, but intrinsics are available anyway
 	if(CMAKE_CL_64)
-		set(CYCLES_SSE2_KERNEL_FLAGS "/fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
-		set(CYCLES_SSE3_KERNEL_FLAGS "/fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
-		set(CYCLES_SSE41_KERNEL_FLAGS "/fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
-		set(CYCLES_AVX_KERNEL_FLAGS "${CYCLES_AVX_ARCH_FLAGS} /fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
-		set(CYCLES_AVX2_KERNEL_FLAGS "${CYCLES_AVX2_ARCH_FLAGS} /fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
+		set(CYCLES_SSE2_KERNEL_FLAGS "${CYCLES_KERNEL_FLAGS}")
+		set(CYCLES_SSE3_KERNEL_FLAGS "${CYCLES_KERNEL_FLAGS}")
+		set(CYCLES_SSE41_KERNEL_FLAGS "${CYCLES_KERNEL_FLAGS}")
+		set(CYCLES_AVX_KERNEL_FLAGS "${CYCLES_AVX_ARCH_FLAGS} ${CYCLES_KERNEL_FLAGS}")
+		set(CYCLES_AVX2_KERNEL_FLAGS "${CYCLES_AVX2_ARCH_FLAGS} ${CYCLES_KERNEL_FLAGS}")
 	else()
-		set(CYCLES_SSE2_KERNEL_FLAGS "/arch:SSE2 /fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
-		set(CYCLES_SSE3_KERNEL_FLAGS "/arch:SSE2 /fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
-		set(CYCLES_SSE41_KERNEL_FLAGS "/arch:SSE2 /fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
-		set(CYCLES_AVX_KERNEL_FLAGS "${CYCLES_AVX_ARCH_FLAGS} /fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
-		set(CYCLES_AVX2_KERNEL_FLAGS "${CYCLES_AVX2_ARCH_FLAGS} /fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
+		set(CYCLES_SSE2_KERNEL_FLAGS "/arch:SSE2 ${CYCLES_KERNEL_FLAGS}")
+		set(CYCLES_SSE3_KERNEL_FLAGS "/arch:SSE2 ${CYCLES_KERNEL_FLAGS}")
+		set(CYCLES_SSE41_KERNEL_FLAGS "/arch:SSE2 ${CYCLES_KERNEL_FLAGS}")
+		set(CYCLES_AVX_KERNEL_FLAGS "${CYCLES_AVX_ARCH_FLAGS} ${CYCLES_KERNEL_FLAGS}")
+		set(CYCLES_AVX2_KERNEL_FLAGS "${CYCLES_AVX2_ARCH_FLAGS} ${CYCLES_KERNEL_FLAGS}")
 	endif()
 
-	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
+	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CYCLES_KERNEL_FLAGS}")
 	set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} /Ox")
 	set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO} /Ox")
 	set(CMAKE_CXX_FLAGS_MINSIZEREL "${CMAKE_CXX_FLAGS_MINSIZEREL} /Ox")
-
-	set(CYCLES_KERNEL_FLAGS "/fp:fast -D_CRT_SECURE_NO_WARNINGS /GS-")
-elseif(CMAKE_COMPILER_IS_GNUCC)
+elseif(CMAKE_COMPILER_IS_GNUCC OR (CMAKE_CXX_COMPILER_ID MATCHES "Clang"))
 	check_cxx_compiler_flag(-msse CXX_HAS_SSE)
 	check_cxx_compiler_flag(-mavx CXX_HAS_AVX)
 	check_cxx_compiler_flag(-mavx2 CXX_HAS_AVX2)
-	set(CYCLES_KERNEL_FLAGS "-ffast-math")
-	if(CXX_HAS_SSE)
-		set(CYCLES_SSE2_KERNEL_FLAGS "-ffast-math -msse -msse2 -mfpmath=sse")
-		set(CYCLES_SSE3_KERNEL_FLAGS "-ffast-math -msse -msse2 -msse3 -mssse3 -mfpmath=sse")
-		set(CYCLES_SSE41_KERNEL_FLAGS "-ffast-math -msse -msse2 -msse3 -mssse3 -msse4.1 -mfpmath=sse")
-	endif()
-	if(CXX_HAS_AVX)
-		set(CYCLES_AVX_KERNEL_FLAGS "-ffast-math -msse -msse2 -msse3 -mssse3 -msse4.1 -mavx -mfpmath=sse")
-	endif()
-	if(CXX_HAS_AVX2)
-		set(CYCLES_AVX2_KERNEL_FLAGS "-ffast-math -msse -msse2 -msse3 -mssse3 -msse4.1 -mavx -mavx2 -mfma -mlzcnt -mbmi -mbmi2 -mf16c -mfpmath=sse")
+
+	# Assume no signal trapping for better code generation.
+	set(CYCLES_KERNEL_FLAGS "-fno-trapping-math")
+	# Avoid overhead of setting errno for NaNs.
+	set(CYCLES_KERNEL_FLAGS "${CYCLES_KERNEL_FLAGS} -fno-math-errno")
+	# Let compiler optimize 0.0 - x without worrying about signed zeros.
+	set(CYCLES_KERNEL_FLAGS "${CYCLES_KERNEL_FLAGS} -fno-signed-zeros")
+
+	if(CMAKE_COMPILER_IS_GNUCC)
+		# Assume no signal trapping for better code generation.
+		set(CYCLES_KERNEL_FLAGS "${CYCLES_KERNEL_FLAGS} -fno-signaling-nans")
+		# Assume a fixed rounding mode for better constant folding.
+		set(CYCLES_KERNEL_FLAGS "${CYCLES_KERNEL_FLAGS} -fno-rounding-math")
 	endif()
-	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -ffast-math -fno-finite-math-only")
-elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-	check_cxx_compiler_flag(-msse CXX_HAS_SSE)
-	check_cxx_compiler_flag(-mavx CXX_HAS_AVX)
-	check_cxx_compiler_flag(-mavx2 CXX_HAS_AVX2)
-	set(CYCLES_KERNEL_FLAGS "-ffast-math")
+
 	if(CXX_HAS_SSE)
-		set(CYCLES_SSE2_KERNEL_FLAGS "-ffast-math -msse -msse2")
-		set(CYCLES_SSE3_KERNEL_FLAGS "-ffast-math -msse -msse2 -msse3 -mssse3")
-		set(CYCLES_SSE41_KERNEL_FLAGS "-ffast-math -msse -msse2 -msse3 -mssse3 -msse4.1")
-	endif()
-	if(CXX_HAS_AVX)
-		set(CYCLES_AVX_KERNEL_FLAGS "-ffast-math -msse -msse2 -msse3 -mssse3 -msse4.1 -mavx")
-	endif()
-	if(CXX_HAS_AVX2)
-		set(CYCLES_AVX2_KERNEL_FLAGS "-ffast-math -msse -msse2 -msse3 -mssse3 -msse4.1 -mavx -mavx2 -mfma -mlzcnt -mbmi -mbmi2 -mf16c")
+		if(CMAKE_COMPILER_IS_GNUCC)
+			set(CYCLES_KERNEL_FLAGS "${CYCLES_KERNEL_FLAGS} -mfpmath=sse")
+		endif()
+
+		set(CYCLES_SSE2_KERNEL_FLAGS "${CYCLES_KERNEL_FLAGS} -msse -msse2")
+		set(CYCLES_SSE3_KERNEL_FLAGS "${CYCLES_SSE2_KERNEL_FLAGS} -msse3 -mssse3")
+		set(CYCLES_SSE41_KERNEL_FLAGS "${CYCLES_SSE3_KERNEL_FLAGS} -msse4.1")
+		if(CXX_HAS_AVX)
+			set(CYCLES_AVX_KERNEL_FLAGS "${CYCLES_SSE41_KERNEL_FLAGS} -mavx")
+		endif()
+		if(CXX_HAS_AVX2)
+			set(CYCLES_AVX2_KERNEL_FLAGS "${CYCLES_SSE41_KERNEL_FLAGS} -mavx -mavx2 -mfma -mlzcnt -mbmi -mbmi2 -mf16c")
+		endif()
 	endif()
-	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -ffast-math -fno-finite-math-only")
+
+	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CYCLES_KERNEL_FLAGS}")
 endif()
 
 if(CXX_HAS_SSE)