[PATCH v3] Change default to -fno-math-errno
Wilco Dijkstra
Wilco.Dijkstra@arm.com
Tue Sep 4 15:27:00 GMT 2018
ping
From: Wilco Dijkstra
Sent: 18 June 2018 15:01
To: GCC Patches
Cc: nd; Joseph Myers
Subject: [PATCH v3] Change default to -fno-math-errno
GCC currently defaults to -fmath-errno. This generates code assuming math
functions set errno and the application checks errno. Few applications
test errno and various systems and math libraries no longer set errno since it
is optional. GCC generates much faster code for simple math functions with
-fno-math-errno such as sqrt and lround (avoiding a call and PLT redirection).
Therefore it is reasonable to change the default to -fno-math-errno. This is
already the case for non-C languages. Only change the default for C99 and
later.
long f(float x) { return lroundf(x) + 1; }
by default:
f:
str x30, [sp, -16]!
bl lroundf
add x0, x0, 1
ldr x30, [sp], 16
ret
With -fno-math-errno:
f:
fcvtas x0, s0
add x0, x0, 1
ret
Passes regress on AArch64. OK for commit?
ChangeLog:
2018-06-18 Wilco Dijkstra <wdijkstr@arm.com>
* common.opt (fmath-errno): Change default to 0.
* opts.c (set_fast_math_flags): Force -fno-math-errno with -ffast-math.
* c-family/c-opts.c (c_common_init_options_struct): Set flag_errno_math
to special value.
(c_common_post_options): Set flag_errno_math default based on language.
doc/
* invoke.texi (-fmath-errno) Update documentation.
testsuite/
* gcc.dg/errno-1.c: Add -fmath-errno.
* gcc.dg/torture/pr68264.c: Likewise.
* gcc.dg/tree-ssa/ssa-dse-15.c: Likewise.
* gcc.target/aarch64/no-inline-lrint_1.c: Likewise.
--
diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c
index bbcb1bb1a9c606a262a1aa362471388987629d06..b13fc122f8baf6aae0b47010be92ffd961b0147a 100644
--- a/gcc/c-family/c-opts.c
+++ b/gcc/c-family/c-opts.c
@@ -208,6 +208,9 @@ c_common_init_options_struct (struct gcc_options *opts)
/* By default, C99-like requirements for complex multiply and divide. */
opts->x_flag_complex_method = 2;
+
+ /* Use a special value so the default can be set after option parsing. */
+ opts->x_flag_errno_math = 2;
}
/* Common initialization before calling option handlers. */
@@ -831,6 +834,11 @@ c_common_post_options (const char **pfilename)
else if (!flag_gnu89_inline && !flag_isoc99)
error ("-fno-gnu89-inline is only supported in GNU99 or C99 mode");
+ /* If -fmath-errno isn't set (or implied by another math option),
+ set the default to -fno-math-errno for C99 and later. */
+ if (flag_errno_math == 2)
+ flag_errno_math = !flag_isoc99 || c_dialect_objc ();
+
/* Default to ObjC sjlj exception handling if NeXT runtime. */
if (flag_objc_sjlj_exceptions < 0)
flag_objc_sjlj_exceptions = flag_next_runtime;
diff --git a/gcc/common.opt b/gcc/common.opt
index d54e8e5601698c73d2c2bc8f354b55f3889a9186..e6fe11d1dcdbb39016242299dd3d76233e2bd976 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1855,7 +1855,7 @@ Common Report Var(flag_lto_report_wpa) Init(0)
Report various link-time optimization statistics for WPA only.
fmath-errno
-Common Report Var(flag_errno_math) Init(1) Optimization SetByCombined
+Common Report Var(flag_errno_math) Init(0) Optimization SetByCombined
Set errno after built-in math functions.
fmax-errors=
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 42832c5a50013d776dff47c6d347f5bc4dbef2d8..aeda219ba0dbe169d9fb2b4358950f2ba32b5c78 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -9783,24 +9783,16 @@ that depend on an exact implementation of IEEE or ISO rules/specifications
for math functions. It may, however, yield faster code for programs
that do not require the guarantees of these specifications.
-@item -fno-math-errno
-@opindex fno-math-errno
-Do not set @code{errno} after calling math functions that are executed
-with a single instruction, e.g., @code{sqrt}. A program that relies on
-IEEE exceptions for math error handling may want to use this flag
-for speed while maintaining IEEE arithmetic compatibility.
+@item -fmath-errno
+@opindex fmath-errno
+Generate code that assumes math functions may set errno. This disables
+inlining of simple math functions like @code{sqrt} and @code{lround}.
-This option is not turned on by any @option{-O} option since
-it can result in incorrect output for programs that depend on
-an exact implementation of IEEE or ISO rules/specifications for
-math functions. It may, however, yield faster code for programs
-that do not require the guarantees of these specifications.
-
-The default is @option{-fmath-errno}.
+A program which relies on math functions setting errno may need to
+use this flag. However note various systems and math libraries never
+set errno.
-On Darwin systems, the math library never sets @code{errno}. There is
-therefore no reason for the compiler to consider the possibility that
-it might, and @option{-fno-math-errno} is the default.
+The default is @option{-fno-math-errno} except in ISO C90 and C++98 modes.
@item -funsafe-math-optimizations
@opindex funsafe-math-optimizations
@@ -21827,8 +21819,8 @@ truncation towards zero.
@item @samp{round}
Conversion from single-precision floating point to signed integer,
rounding to the nearest integer and ties away from zero.
-This corresponds to the @code{__builtin_lroundf} function when
-@option{-fno-math-errno} is used.
+This corresponds to the @code{__builtin_lroundf} function unless
+@option{-fmath-errno} is used.
@item @samp{floatis}, @samp{floatus}, @samp{floatid}, @samp{floatud}
Conversion from signed or unsigned integer types to floating-point types.
diff --git a/gcc/opts.c b/gcc/opts.c
index 33efcc0d6e7db73ba60cab62ef146e976e75ca21..a6f228a53e1baa505a477a273fad3d00364f6893 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -2581,8 +2581,6 @@ set_fast_math_flags (struct gcc_options *opts, int set)
}
if (!opts->frontend_set_flag_finite_math_only)
opts->x_flag_finite_math_only = set;
- if (!opts->frontend_set_flag_errno_math)
- opts->x_flag_errno_math = !set;
if (set)
{
if (opts->frontend_set_flag_excess_precision_cmdline
@@ -2595,6 +2593,8 @@ set_fast_math_flags (struct gcc_options *opts, int set)
opts->x_flag_rounding_math = 0;
if (!opts->frontend_set_flag_cx_limited_range)
opts->x_flag_cx_limited_range = 1;
+ if (!opts->frontend_set_flag_errno_math)
+ opts->x_flag_errno_math = 0;
}
}
diff --git a/gcc/testsuite/gcc.dg/errno-1.c b/gcc/testsuite/gcc.dg/errno-1.c
index 0dfb00087dee04cd5ff1e916149c0c13c9b87b20..25739e4a862ca9a9c05157d3abc87216eb27ea7d 100644
--- a/gcc/testsuite/gcc.dg/errno-1.c
+++ b/gcc/testsuite/gcc.dg/errno-1.c
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2" } */
+/* { dg-options "-O2 -fmath-errno" } */
#include <errno.h>
#include <stdlib.h>
diff --git a/gcc/testsuite/gcc.dg/torture/pr68264.c b/gcc/testsuite/gcc.dg/torture/pr68264.c
index 9294d5aedb79de1b91b3074e34b089b100031d54..56d7bf7bc64545566d7127a329f244045a0f2afc 100644
--- a/gcc/testsuite/gcc.dg/torture/pr68264.c
+++ b/gcc/testsuite/gcc.dg/torture/pr68264.c
@@ -1,5 +1,6 @@
/* { dg-do run } */
/* { dg-add-options ieee } */
+/* { dg-additional-options "-fmath-errno" } */
/* { dg-require-effective-target fenv_exceptions } */
#include <fenv.h>
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-15.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-15.c
index 43a41c8eb38db1c930923f1bb0fd9d1689fac826..134febf96d38128a0f5ebf7175f137c7aefc90bc 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-15.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-15.c
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-dse1-details" } */
+/* { dg-options "-O2 -fdump-tree-dse1-details -fmath-errno" } */
void *foo (int *p)
{
diff --git a/gcc/testsuite/gcc.target/aarch64/no-inline-lrint_1.c b/gcc/testsuite/gcc.target/aarch64/no-inline-lrint_1.c
index d5e9200562c166ace4d8e72d9a9f560e35846b29..229b456576a81d99427625a3e3f6cc63e937eb5a 100644
--- a/gcc/testsuite/gcc.target/aarch64/no-inline-lrint_1.c
+++ b/gcc/testsuite/gcc.target/aarch64/no-inline-lrint_1.c
@@ -1,6 +1,6 @@
/* { dg-do compile } */
/* { dg-require-effective-target lp64 } */
-/* { dg-options "-O3" } */
+/* { dg-options "-O3 -fmath-errno" } */
#include "lrint-matherr.h"
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