[PATCH 3/3] arm: reorder assembler architecture directives [PR101723]

Richard Earnshaw rearnsha@arm.com
Mon Aug 2 14:56:51 GMT 2021


A change to the way gas interprets the .fpu directive in binutils-2.34
means that issuing .fpu will clear any features set by .arch_extension
that apply to the floating point or simd units.  This unfortunately
causes problems for more recent versions of the architecture because
we currently emit .arch, .arch_extension and .fpu directives at
different times and try to suppress redundant changes.

This change addresses this by firstly unifying all the places where we
emit these directives to a single block of code and secondly
(re)emitting all the directives if any changes have been made to the
target options.  Whilst this is slightly more than the strict minimum
it should be enough to catch all cases where a change could have
happened.  The new code also emits the directives in the order: .arch,
.fpu, .arch_extension.  This ensures that the additional architectural
extensions are not removed by a later .fpu directive.

Whilst writing this patch I also noticed that in the corner case where
the last function to be compiled had a non-standard set of
architecture flags, the assembler would add an incorrect set of
derived attributes for the file as a whole.  Instead of reflecting the
command-line options it would reflect the flags from the last file in
the function.  To address this I've also added a call to re-emit the
flags from the asm_file_end callback so the assembler will be in the
correct state when it finishes processing the intput.

There's some slight churn to the testsuite as a consequence of this,
because previously we had a hack to suppress emitting a .fpu directive
for one specific case, but with the new order this is no-longer
necessary.

gcc/ChangeLog:

	PR target/101723
	* config/arm/arm-cpus.in (generic-armv7-a): Add quirk to suppress
	writing .cpu directive in asm output.
	* config/arm/arm.c (arm_identify_fpu_from_isa): New variable.
	(arm_last_printed_arch_string): Delete.
	(arm_last-printed_fpu_string): Delete.
	(arm_configure_build_target): If use of floating-point/SIMD is
	disabled, remove all fp/simd related features from the target ISA.
	(last_arm_targ_options): New variable.
	(arm_print_asm_arch_directives): Add new parameters.  Change order
	of emitted directives and handle all cases here.
	(arm_file_start): Always call arm_print_asm_arch_directives, move
	all generation of .arch/.arch_extension here.
	(arm_file_end): Call arm_print_asm_arch.
	(arm_declare_function_name): Call arm_print_asm_arch_directives
	instead of printing .arch/.fpu directives directly.

gcc/testsuite/ChangeLog:

	PR target/101723
	* gcc.target/arm/cortex-m55-nofp-flag-hard.c: Update expected output.
	* gcc.target/arm/cortex-m55-nofp-flag-softfp.c: Likewise.
	* gcc.target/arm/cortex-m55-nofp-nomve-flag-softfp.c: Likewise.
	* gcc.target/arm/mve/intrinsics/mve_fpu1.c: Convert to dg-do assemble.
	Add a non-no-op function body.
	* gcc.target/arm/mve/intrinsics/mve_fpu2.c: Likewise.
	* gcc.target/arm/pr98636.c (dg-options): Add -mfloat-abi=softfp.
	* gcc.target/arm/attr-neon.c: Tighten scan-assembler tests.
	* gcc.target/arm/attr-neon2.c: Use -Ofast, convert test to use
	check-function-bodies.
	* gcc.target/arm/attr-neon3.c: Likewise.
---
 gcc/config/arm/arm-cpus.in                    |   1 +
 gcc/config/arm/arm.c                          | 186 ++++++++----------
 gcc/testsuite/gcc.target/arm/attr-neon.c      |   9 +-
 gcc/testsuite/gcc.target/arm/attr-neon2.c     |  35 ++--
 gcc/testsuite/gcc.target/arm/attr-neon3.c     |  43 ++--
 .../arm/cortex-m55-nofp-flag-hard.c           |   2 +-
 .../arm/cortex-m55-nofp-flag-softfp.c         |   2 +-
 .../arm/cortex-m55-nofp-nomve-flag-softfp.c   |   2 +-
 .../gcc.target/arm/mve/intrinsics/mve_fpu1.c  |   5 +-
 .../gcc.target/arm/mve/intrinsics/mve_fpu2.c  |   5 +-
 gcc/testsuite/gcc.target/arm/pr98636.c        |   3 +-
 11 files changed, 149 insertions(+), 144 deletions(-)

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