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Go patch committed: Build math library with -funsafe-math-optimizations
- From: Ian Lance Taylor <iant at google dot com>
- To: gcc-patches at gcc dot gnu dot org, gofrontend-dev at googlegroups dot com
- Date: Wed, 08 Feb 2012 11:38:22 -0800
- Subject: Go patch committed: Build math library with -funsafe-math-optimizations
The master Go math library uses assembler code on 386 processors to take
advantage of 387 instructions. This patch lets gccgo do the same thing,
by compiling the math library with -funsafe-math-optimizations. I also
pass -mfancy-math-387, although that is the default. It would not be
appropriate to compile all Go code with -funsafe-math-optimizations, of
course, but the math library is designed to handle it.
The compiler currently rewrites calls to, e.g., acos to call acosl
instead when using excess precision. This also enables the use of
assembler routines on 387. I tweaked the compiler to only do this when
optimizing, which is probably how it should have been done anyhow. (At
some point this code will move into the gcc interface out of the
frontend proper.)
With this change the math library no longer refers to functions like
acosl on 386 systems--the operations are done inline using 387
instructions--which should address some portability problems.
Bootstrapped and ran Go testsuite on x86_64-unknown-linux-gnu (32-bit
and 64-bit mode). Committed to mainline.
Ian
diff -r 69a7e6220af1 go/expressions.cc
--- a/go/expressions.cc Tue Feb 07 22:16:02 2012 -0800
+++ b/go/expressions.cc Wed Feb 08 11:29:04 2012 -0800
@@ -10027,7 +10027,8 @@
// This is to support builtin math functions when using 80387 math.
tree excess_type = NULL_TREE;
- if (TREE_CODE(fndecl) == FUNCTION_DECL
+ if (optimize
+ && TREE_CODE(fndecl) == FUNCTION_DECL
&& DECL_IS_BUILTIN(fndecl)
&& DECL_BUILT_IN_CLASS(fndecl) == BUILT_IN_NORMAL
&& nargs > 0
diff -r 69a7e6220af1 libgo/Makefile.am
--- a/libgo/Makefile.am Tue Feb 07 22:16:02 2012 -0800
+++ b/libgo/Makefile.am Wed Feb 08 11:29:04 2012 -0800
@@ -1959,7 +1959,9 @@
math/math.lo.dep: $(go_math_files)
$(BUILDDEPS)
math/math.lo: $(go_math_files)
- $(BUILDPACKAGE)
+ $(MKDIR_P) $(@D)
+ files=`echo $^ | sed -e 's/[^ ]*\.gox//g'`; \
+ $(LTGOCOMPILE) $(MATH_FLAG) -I . -c -fgo-prefix="libgo_$(@D)" -o $@ $$files
math/check: $(CHECK_DEPS)
@$(CHECK)
.PHONY: math/check
diff -r 69a7e6220af1 libgo/configure.ac
--- a/libgo/configure.ac Tue Feb 07 22:16:02 2012 -0800
+++ b/libgo/configure.ac Wed Feb 08 11:29:04 2012 -0800
@@ -522,6 +522,23 @@
fi
AC_SUBST(STRINGOPS_FLAG)
+dnl For x86 we want to compile the math library with -mfancy-math-387
+dnl -funsafe-math-optimizations so that we can use the builtin
+dnl instructions directly.
+AC_CACHE_CHECK([whether compiler supports -mfancy-math-387],
+[libgo_cv_c_fancymath],
+[CFLAGS_hold=$CFLAGS
+CFLAGS="$CFLAGS -mfancy-math-387"
+AC_COMPILE_IFELSE([int i;],
+[libgo_cv_c_fancymath=yes],
+[libgo_cv_c_fancymath=no])
+CFLAGS=$CFLAGS_hold])
+MATH_FLAG=
+if test "$libgo_cv_c_fancymath" = yes; then
+ MATH_FLAG="-mfancy-math-387 -funsafe-math-optimizations"
+fi
+AC_SUBST(MATH_FLAG)
+
CFLAGS_hold=$CFLAGS
CFLAGS="$CFLAGS -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE"
AC_CHECK_TYPES([off64_t])