From 09ce68aede661dc61819332cec5cb82218fd91e7 Mon Sep 17 00:00:00 2001
From: Nils Kohl <nils.kohl@fau.de>
Date: Mon, 20 Mar 2023 10:20:37 +0100
Subject: [PATCH] Half precision support for gcc.
---
CMakeLists.txt | 29 +++++++++++++++++++------
apps/tools/MixedPrecision/CheckFP16.cpp | 8 +++----
src/core/DataTypes.h | 17 ++++++++-------
3 files changed, 35 insertions(+), 19 deletions(-)
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 54b37fb1e..b6962d6dc 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1256,13 +1256,28 @@ endif()
## Half precision
##
############################################################################################################################
-if ( WALBERLA_BUILD_WITH_HALF_PRECISION_SUPPORT )
- message( STATUS "Configuring with *experimental* half precision (float16) support. You better know what you are doing." )
- if ( NOT WALBERLA_OPTIMIZE_FOR_LOCALHOST )
- message( WARNING "[WALBERLA_BUILD_WITH_HALF_PRECISION_SUPPORT] "
- "You are not optimizing for localhost. Linker errors could occur. Consider also enabling WALBERLA_OPTIMIZE_FOR_LOCALHOST!" )
- endif()
-endif()
+if (WALBERLA_BUILD_WITH_HALF_PRECISION_SUPPORT)
+ if (WALBERLA_CXX_COMPILER_IS_GNU OR WALBERLA_CXX_COMPILER_IS_CLANG)
+ message(STATUS "Configuring with *experimental* half precision (float16) support. You better know what you are doing.")
+ if (WALBERLA_CXX_COMPILER_IS_GNU AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 12.0.0)
+ message(WARNING "[WALBERLA_BUILD_WITH_HALF_PRECISION_SUPPORT] "
+ "Half precision support for gcc has only been tested with version >= 12. "
+ "You are using a previous version - it may not work correctly.")
+ endif ()
+ if (WALBERLA_CXX_COMPILER_IS_CLANG AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 15.0.0)
+ message(WARNING "[WALBERLA_BUILD_WITH_HALF_PRECISION_SUPPORT] "
+ "Half precision support for clang has only been tested with version >= 15. "
+ "You are using a previous version - it may not work correctly.")
+ endif ()
+ if (NOT WALBERLA_OPTIMIZE_FOR_LOCALHOST)
+ message(WARNING "[WALBERLA_BUILD_WITH_HALF_PRECISION_SUPPORT] "
+ "You are not optimizing for localhost. Linker errors could occur. Consider also enabling WALBERLA_OPTIMIZE_FOR_LOCALHOST!")
+ endif ()
+ else ()
+ message(FATAL_ERROR "[WALBERLA_BUILD_WITH_HALF_PRECISION_SUPPORT] "
+ "Half precision support is currently only available for gcc and clang.")
+ endif ()
+endif ()
############################################################################################################################
# Documentation Generation
diff --git a/apps/tools/MixedPrecision/CheckFP16.cpp b/apps/tools/MixedPrecision/CheckFP16.cpp
index 24e29e1cf..7c84676de 100644
--- a/apps/tools/MixedPrecision/CheckFP16.cpp
+++ b/apps/tools/MixedPrecision/CheckFP16.cpp
@@ -77,8 +77,8 @@ int main(int argc, char** argv)
WALBERLA_LOG_INFO_ON_ROOT(" Casting and output compiles.")
WALBERLA_LOG_INFO_ON_ROOT(" - Basic arithmetic check: ")
- float16 x = 1.2f16;
- float16 y = -1.8f16;
+ auto x = float16(1.2);
+ auto y = float16(-1.8);
float64 z = -0.6;
float16 sum = x + y;
WALBERLA_LOG_INFO_ON_ROOT(" " << (double) x << " + " << (double) y << " == " << (float64) (x + y) << "")
@@ -113,11 +113,11 @@ int main(int argc, char** argv)
std::vector< float64 > v64(vsize, 0.01);
std::vector< float32 > v32(vsize, 0.01f);
- std::vector< float16 > v16(vsize, 0.01f16);
+ std::vector< float16 > v16(vsize, float16(0.01));
std::vector< float64 > vv64(vsize, 0.02);
std::vector< float32 > vv32(vsize, 0.02f);
- std::vector< float16 > vv16(vsize, 0.02f16);
+ std::vector< float16 > vv16(vsize, float16(0.02));
std::vector< float64 > r64(vsize);
std::vector< float32 > r32(vsize);
diff --git a/src/core/DataTypes.h b/src/core/DataTypes.h
index 951e1413d..bae5b7651 100644
--- a/src/core/DataTypes.h
+++ b/src/core/DataTypes.h
@@ -167,7 +167,6 @@ using real_t = double;
using real_t = float;
#endif
-
/// Half precision support. Experimental. Use carefully.
///
/// This feature is experimental, since it strictly depends on the underlying architecture and compiler support.
@@ -176,19 +175,21 @@ using real_t = float;
/// Only bandwidth bound code may therefore benefit. None of this is guaranteed, and may change in the future.
///
#ifdef WALBERLA_BUILD_WITH_HALF_PRECISION_SUPPORT
-#ifdef WALBERLA_CXX_COMPILER_IS_CLANG
+# if defined(WALBERLA_CXX_COMPILER_IS_CLANG) || defined(WALBERLA_CXX_COMPILER_IS_GNU)
/// Clang version must be 15 or higher for x86 half precision support.
+/// GCC version must be 12 or higher for x86 half precision support.
/// Also support seems to require SSE, so ensure that respective instruction sets are enabled.
/// See
/// https://clang.llvm.org/docs/LanguageExtensions.html#half-precision-floating-point
+/// https://gcc.gnu.org/onlinedocs/gcc/Half-Precision.html
/// for more information.
-using half = _Float16;
-#else
-static_assert( false, "Attempting to built walberla with half precision support.\n"
- "However, the compiler you chose is not suited for that, or we simply have not implemented "
- "support for half precision and your compiler." )
-#endif
+using half = _Float16;
using float16 = half;
+# else
+static_assert(false, "\n\n### Attempting to built walberla with half precision support.\n"
+ "### However, the compiler you chose is not suited for that, or we simply have not implemented "
+ "support for half precision and your compiler.\n");
+# endif
#endif
using float32 = float;
using float64 = double;
--
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