https://gcc.gnu.org/g:7d6c6a0d15c136a68d066c60da0f48265a2b1886
commit r15-3606-g7d6c6a0d15c136a68d066c60da0f48265a2b1886
Author: Richard Earnshaw <rearn...@arm.com>
Date: Wed Sep 11 17:06:12 2024 +0100
arm: Allow -mcpu and -march options to be unset
The compiler will warn if the architectural specification derived from
a -mcpu option is not the same as that specified by -march. This is
because it was never intended that the two should be used at the same
time: -mcpu=<name> is supposed to be shorthand for -mtune=<name>
-march=arch-of(<name>).
Unfortunately, there are times when the two options passed to the
compiler may come from distinct sources: one example is makefiles
which accumulate options; another is the testsuite itself, when some
tests require a particular architecture setting to be useful - only
running the tests when the compiler/testsuite configuration exactly
matched the requirements would make regression testing especially hard
(we have too many permutations).
So this patch allows a user to cancel any earlier setting of a
particular flag and to make the compiler behave as though it was never
passed. The intended usecase is (sources of options are shown in
parenthesis, but that's just for grouping:
(-march=armv7-a+simd) (-march=unset -mcpu=cortex-m33)
The option processing logic will now simplify this to:
-mcpu=cortex-m33
A useful corollary of this is that
-march=armv7-a -march=unset
will now cause the compiler to behave as though neither the
architecture nor the CPU was ever set and to default back to the
configure-time settings.
gcc/ChangeLog:
* config/arm/arm.h (OPTION_DEFAULT_SPECS): Allow -mcpu and -march
to be unset.
(ARCH_CPU_CLEANUP_SPECS): Likewise
(DRIVER_SELF_SPECS): Add ARCH_CPU_CLEANUP_SPECS
* doc/invoke.texi (arm: -mcpu= and -march=): Document use of
'unset'.
Diff:
---
gcc/config/arm/arm.h | 14 +++++++++++---
gcc/doc/invoke.texi | 12 ++++++++++++
2 files changed, 23 insertions(+), 3 deletions(-)
diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
index 0cd5d733952d..b092ba6ffe01 100644
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -394,9 +394,11 @@ emission of floating point pcs attributes. */
TARGET_MODE_CHECK that also takes into account the selected CPU and
architecture. */
#define OPTION_DEFAULT_SPECS \
- {"arch", "%{!march=*:%{!mcpu=*:-march=%(VALUE)}}" }, \
- {"cpu", "%{!march=*:%{!mcpu=*:-mcpu=%(VALUE)}}" }, \
- {"tune", "%{!mcpu=*:%{!mtune=*:-mtune=%(VALUE)}}" }, \
+ {"arch", "%{!march=*|march=unset:"\
+ "%{!mcpu=*|mcpu=unset:%<march=* %<mcpu=* -march=%(VALUE)}}" }, \
+ {"tune", "%{!mcpu=*|mcpu=unset:%{!mtune=*:-mtune=%(VALUE)}}" }, \
+ {"cpu", "%{!march=*|march=unset:"\
+ "%{!mcpu=*|mcpu=unset:%<march=* %<mcpu=* -mcpu=%(VALUE)}}" }, \
{"float", "%{!mfloat-abi=*:-mfloat-abi=%(VALUE)}" }, \
{"fpu", "%{!mfpu=*:-mfpu=%(VALUE)}"}, \
{"abi", "%{!mabi=*:-mabi=%(VALUE)}"}, \
@@ -2538,6 +2540,11 @@ const char *arm_be8_option (int argc, const char **argv);
#define TARGET_MODE_SPECS \
" %{!marm:%{!mthumb:%:target_mode_check(%{march=*:arch %*;mcpu=*:cpu
%*;:})}}"
+/* Cleanup any stray -march=/-mcpu= if either is followed by "unset". */
+#define ARCH_CPU_CLEANUP_SPECS \
+ " %{march=unset:%<march=*} " \
+ " %{mcpu=unset:%<mcpu=*} "
+
/* Generate a canonical string to represent the architecture selected. */
#define ARCH_CANONICAL_SPECS \
" -march=%:canon_arch(%{mcpu=*: cpu %*} " \
@@ -2559,6 +2566,7 @@ const char *arm_be8_option (int argc, const char **argv);
individual rules so that any option suppression (%<opt...)is
completed before starting subsequent rules. */
#define DRIVER_SELF_SPECS \
+ ARCH_CPU_CLEANUP_SPECS, \
MCPU_MTUNE_NATIVE_SPECS, \
TARGET_MODE_SPECS, \
MULTILIB_ARCH_CANONICAL_SPECS, \
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index c2078a7eef35..a6cd5111d47c 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -23492,6 +23492,12 @@ of the build computer. At present, this feature is
only supported on
GNU/Linux, and not all architectures are recognized. If the auto-detect
is unsuccessful the option has no effect.
+@option{-march=unset} causes the compiler to ignore any
+@option{-march=@dots{}} options that appear earlier on the command line
+and behave as if the option was never passed. This is useful to avoid
+warnings about conflicting CPU and architecture options when the two
+produce different architecture specifications.
+
@opindex mtune
@item -mtune=@var{name}
This option specifies the name of the target ARM processor for
@@ -23654,6 +23660,12 @@ of the build computer. At present, this feature is
only supported on
GNU/Linux, and not all architectures are recognized. If the auto-detect
is unsuccessful the option has no effect.
+@option{-mcpu=unset} causes the compiler to ignore any
+@option{-mcpu=@dots{}} options that appear earlier on the command line
+and behave as if the option was never passed. This is useful to avoid
+warnings about conflicting CPU and architecture options when the two
+produce different architecture specifications.
+
@opindex mfpu
@item -mfpu=@var{name}
This specifies what floating-point hardware (or hardware emulation) is
