This patch adds support to the ARM backend to avoid denormals by setting
the VFP flush-to-zero bit when linking with -ffast-math and similar
options. The mechanism used to accomplish this is a constructor in
libgcc that is conditionally linked in via STARTFILE_SPEC; it's
basically identical to what a number of other backends are already doing
here (Aarch64, i386, MIPS, etc).
I tested this by verifying that linking with -ffast-math on the GCC
command line causes crtfastmath.o to be passed on the ld command line.
I built libgcc with a variety of configuration options to verify that
the constructor is suppressed for soft-float targets, that it builds
successfully for Thumb-2 with VFP, etc. I also regression-tested the
gcc testsuite on an arm-none-linux-gnueabi build configured for
-march=armv8-a with VFP floating point enabled.
OK to commit?
-Sandra
2014-11-08 Sandra Loosemore san...@codesourcery.com
Chris Jones chr...@nvidia.com
Joshua Conner jcon...@nvidia.com
gcc/
* config/arm/unknown-elf.h (STARTFILE_SPEC): Add conditional
linking of crtfastmath.o.
* config/arm/linux-eabi.h (STARTFILE_SPEC): Likewise.
libgcc/
* config.host (arm*-*-linux*): Add support for crtfastmath.o.
(arm*-*-uclinux*): Likewise.
(arm*-*-eabi* | arm*-*-rtems*): Likewise.
* config/arm/crtfastmath.c: New file.
Index: gcc/config/arm/unknown-elf.h
===
--- gcc/config/arm/unknown-elf.h (revision 216500)
+++ gcc/config/arm/unknown-elf.h (working copy)
@@ -32,7 +32,9 @@
#define UNKNOWN_ELF_STARTFILE_SPEC crti%O%s crtbegin%O%s crt0%O%s
#undef STARTFILE_SPEC
-#define STARTFILE_SPEC UNKNOWN_ELF_STARTFILE_SPEC
+#define STARTFILE_SPEC \
+ %{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s} \
+ UNKNOWN_ELF_STARTFILE_SPEC
#define UNKNOWN_ELF_ENDFILE_SPEC crtend%O%s crtn%O%s
Index: gcc/config/arm/linux-eabi.h
===
--- gcc/config/arm/linux-eabi.h (revision 216500)
+++ gcc/config/arm/linux-eabi.h (working copy)
@@ -107,6 +107,7 @@
#undef ENDFILE_SPEC
#define ENDFILE_SPEC \
+ %{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s} \
LINUX_OR_ANDROID_LD (GNU_USER_TARGET_ENDFILE_SPEC, ANDROID_ENDFILE_SPEC)
/* Use the default LIBGCC_SPEC, not the version in linux-elf.h, as we
Index: libgcc/config.host
===
--- libgcc/config.host (revision 216500)
+++ libgcc/config.host (working copy)
@@ -370,14 +370,15 @@ arm*-*-netbsdelf*)
tmake_file=$tmake_file arm/t-arm arm/t-netbsd t-slibgcc-gld-nover
;;
arm*-*-linux*) # ARM GNU/Linux with ELF
- tmake_file=${tmake_file} arm/t-arm t-fixedpoint-gnu-prefix
+ tmake_file=${tmake_file} arm/t-arm t-fixedpoint-gnu-prefix t-crtfm
tmake_file=${tmake_file} arm/t-elf arm/t-bpabi arm/t-linux-eabi t-slibgcc-libgcc
tm_file=$tm_file arm/bpabi-lib.h
unwind_header=config/arm/unwind-arm.h
tmake_file=$tmake_file t-softfp-sfdf t-softfp-excl arm/t-softfp t-softfp
+ extra_parts=$extra_parts crtfastmath.o
;;
arm*-*-uclinux*) # ARM ucLinux
- tmake_file=${tmake_file} t-fixedpoint-gnu-prefix
+ tmake_file=${tmake_file} t-fixedpoint-gnu-prefix t-crtfm
tmake_file=$tmake_file arm/t-arm arm/t-elf t-softfp-sfdf t-softfp-excl arm/t-softfp t-softfp
tmake_file=${tmake_file} arm/t-bpabi
tm_file=$tm_file arm/bpabi-lib.h
@@ -389,7 +390,7 @@ arm*-*-eabi* | arm*-*-symbianelf* | arm*
tm_file=$tm_file arm/bpabi-lib.h
case ${host} in
arm*-*-eabi* | arm*-*-rtems*)
- tmake_file=${tmake_file} arm/t-bpabi
+ tmake_file=${tmake_file} arm/t-bpabi t-crtfm
extra_parts=crtbegin.o crtend.o crti.o crtn.o
;;
arm*-*-symbianelf*)
Index: libgcc/config/arm/crtfastmath.c
===
--- libgcc/config/arm/crtfastmath.c (revision 0)
+++ libgcc/config/arm/crtfastmath.c (revision 0)
@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2014 Free Software Foundation, Inc.
+ *
+ * This file is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 3, or (at your option) any
+ * later version.
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * Under Section 7 of GPL version 3, you are granted additional
+ * permissions described in the GCC Runtime Library Exception, version
+ * 3.1, as published by the Free Software Foundation.
+ *
+ * You should have received a copy of the GNU General Public License and
+ * a copy of the GCC Runtime Library Exception along with this program;
+ * see the files COPYING3 and COPYING.RUNTIME
