Better ISR prologues by supporting GASes __gcc_isr pseudo insn.

gcc/
	Better ISR prologues by supporting GASes __gcc_isr pseudo insn.
	PR target/20296
	PR target/81268
	* configure.ac [target=avr]: Add GAS check for -mgcc-isr.
	(HAVE_AS_AVR_MGCCISR_OPTION):  If so, AC_DEFINE it.
	* config.in: Regenerate.
	* configure: Regenerate.
	* doc/extend.texi (AVR Function Attributes) <no_gccisr>: Document it.
	* doc/invoke.texi (AVR Options) <-mgas-isr-prologues>: Document it.
	* config/avr/avr.opt (-mgas-isr-prologues): New option and...
	(TARGET_GASISR_PROLOGUES): ...target mask.
	* common/config/avr/avr-common.c
	(avr_option_optimization_table) [OPT_LEVELS_1_PLUS_NOT_DEBUG]:
	Set -mgas-isr-prologues.
	* config/avr/avr-passes.def (avr_pass_pre_proep): Add
	INSERT_PASS_BEFORE for it.
	* config/avr/avr-protos.h (make_avr_pass_pre_proep): New proto.
	* config/avr/avr.c (avr_option_override)
	[!HAVE_AS_AVR_MGCCISR_OPTION]: Unset TARGET_GASISR_PROLOGUES.
	(avr_no_gccisr_function_p, avr_hregs_split_reg): New static functions.
	(avr_attribute_table) <no_gccisr>: Add new function attribute.
	(avr_set_current_function) <is_no_gccisr>: Init machine field.
	(avr_pass_data_pre_proep, avr_pass_pre_proep): New pass data
	and rtl_opt_pass.
	(make_avr_pass_pre_proep): New function.
	(emit_push_sfr) <treg>: Add argument to function and use it
	instead of TMP_REG.
	(avr_expand_prologue) [machine->gasisr.maybe]: Emit gasisr insn
	and set machine->gasisr.yes.
	(avr_expand_epilogue) [machine->gasisr.yes]: Similar.
	(avr_asm_function_end_prologue) [machine->gasisr.yes]: Add
	__gcc_isr.n_pushed to .L__stack_usage.
	(TARGET_ASM_FINAL_POSTSCAN_INSN): Define to...
	(avr_asm_final_postscan_insn): ...this new static function.
	* config/avr/avr.h (machine_function)
	<is_no_gccisr, use_L__stack_usage>: New fields.
	<gasisr, gasisr.yes, gasisr.maybe, gasisr.regno>: New fields.
	* config/avr/avr.md (UNSPECV_GASISR): Add unspecv enum.
	(GASISR_Prologue, GASISR_Epilogue, GASISR_Done): New define_constants.
	(gasisr, *gasisr): New expander and insn.
	* config/avr/gen-avr-mmcu-specs.c (print_mcu)
	[HAVE_AS_AVR_MGCCISR_OPTION]: Print asm_gccisr spec.
	* config/avr/specs.h (ASM_SPEC) <asm_gccisr>: Add sub spec.

From-SVN: r250093

1 files changed, 14 insertions, 1 deletions

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index aa848bb..4982f7c 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -661,7 +661,8 @@ Objective-C and Objective-C++ Dialects}.
 @emph{AVR Options}
 @gccoptlist{-mmcu=@var{mcu}  -mabsdata  -maccumulate-args @gol
 -mbranch-cost=@var{cost} @gol
--mcall-prologues  -mint8  -mn_flash=@var{size}  -mno-interrupts @gol
+-mcall-prologues  -mgas-isr-prologues  -mint8 @gol
+-mn_flash=@var{size}  -mno-interrupts @gol
 -mrelax  -mrmw  -mstrict-X  -mtiny-stack  -mfract-convert-truncate @gol
 -mshort-calls  -nodevicelib @gol
 -Waddr-space-convert  -Wmisspelled-isr}
@@ -15977,6 +15978,18 @@ integers. The default branch cost is 0.
 Functions prologues/epilogues are expanded as calls to appropriate
 subroutines.  Code size is smaller.
 
+@item -mgas-isr-prologues
+@opindex mgas-isr-prologues
+Interrupt service routines (ISRs) may use the @code{__gcc_isr} pseudo
+instruction supported by GNU Binutils, see the
+@w{@uref{https://sourceware.org/binutils/docs/as/AVR_002dDependent.html,AVR assembler manual}}
+for details.
+If this option is on, the feature can still be disabled for individual
+ISRs by means of the @ref{AVR Function Attributes,,@code{no_gccisr}}
+function attribute.  This feature is activated per default
+if optimization is on (but not with @option{-Og}, @pxref{Optimize Options}),
+and if GNU Binutils support @w{@uref{https://sourceware.org/PR21683,PR21683}}.
+
 @item -mint8
 @opindex mint8
 Assume @code{int} to be 8-bit integer.  This affects the sizes of all types: a