Background: avr-gcc currently generated ISR prologues and epilogues less efficient than possible. This is due to avr back-end design and decisions. Solving this in avr-gcc alone would be inappropriately amount of work and instability, maybe even reducing code performance in other places than ISRs. This is the reason for why https://gcc.gnu.org/bugzilla/show_bug.cgi?id=20296 is open for > 12 years now and has been suspended. A comined GCC + GAS approach would be feasible, and this PR is the GAS part: GAS implements a __gcc_isr pseudo-instruction which scans the code and emits parts of ISR prologue and epilogue. __gcc_isr 1: GAS will replace it by an ISR prologue chunk (at most 6 insns). __gcc_isr 2: GAS will replace it by an ISR epilogue chunk (at most 5 insns). __gcc_isr 0, Rx: Scan the code since the last prologue chunk and replace all encountered prologue and epilogue chunks by appropriate code. Rx is general purpose register. During parse (md_assemble), prologue and epilogue chunks are represented as rs_machine_dependent fragments. If "__gcc_isr 0, Rx" is seen, all rs_machine_dependent fragments in the current chain are transformed into ordinary rs_fill code fragments of then known fixed size. After parse (md_pre_output_hook) a sanity check is performed which reports any dangling chunks. __gcc_isr is only available with the new command line option -mgcc-isr
Created attachment 10232 [details] bin-pr21683-gccisr.diff: Proposed patch. / PR gas/21683 * include/opcode/avr.h (AVR_INSN): Add one for __gcc_isr. gas/ PR gas/21683 * doc/c-avr.texi (AVR Options) <-mgcc-isr>: Document it. (AVR Pseudo Instructions): New node. * config/tc-avr.h (md_pre_output_hook): Define to avr_pre_output_hook. (md_undefined_symbol): Define to avr_undefined_symbol. (avr_pre_output_hook, avr_undefined_symbol): New protos. * config/tc-avr.c (struc-symbol.h): Include it. (ISR_CHUNK_Done, ISR_CHUNK_Prologue, ISR_CHUNK_Epilogue): New enums. (avr_isr, avr_gccisr_opcode) (avr_no_sreg_hash, avr_no_sreg): New static variables. (avr_opt_s) <have_gccisr>: Add field. (avr_opt): Add initializer for have_gccisr. (enum options) <OPTION_HAVE_GCCISR>: Add enum. (md_longopts) <"mgcc-isr">: Add entry. (md_show_usage): Document -mgcc-isr. (md_parse_option) [OPTION_HAVE_GCCISR]: Handle it. (md_undefined_symbol): Remove. (avr_undefined_symbol, avr_pre_output_hook): New fuctions. (md_begin) <avr_no_sreg_hash, avr_gccisr_opcode>: Initialize them. (avr_operand) <pregno>: Add argument and set *pregno if function is called for a register constraint. [N]: Handle constraint. (avr_operands) <avr_operand>: Pass 5th parameter to calls. [avr_opt.have_gccisr]: Call avr_update_gccisr. Call avr_gccisr_operands instead of avr_operands. (avr_update_gccisr, avr_emit_insn, avr_patch_gccisr_frag) (avr_gccisr_operands, avr_check_gccisr_done): New static functions. * testsuite/gas/avr/gccisr-01.d: New test. * testsuite/gas/avr/gccisr-01.s: New test. * testsuite/gas/avr/gccisr-02.d: New test. * testsuite/gas/avr/gccisr-02.s: New test. * testsuite/gas/avr/gccisr-03.d: New test. * testsuite/gas/avr/gccisr-03.s: New test.
The master branch has been updated by Nick Clifton <nickc@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=32f76c677333510350f21a40db062a8d17995c53 commit 32f76c677333510350f21a40db062a8d17995c53 Author: Georg-Johann Lay <avr@gjlay.de> Date: Fri Jun 30 16:37:39 2017 +0100 Add support for a __gcc_isr pseudo isntruction to the AVR assembler. PR gas/21683 include * opcode/avr.h (AVR_INSN): Add one for __gcc_isr. gas * doc/c-avr.texi (AVR Options) <-mgcc-isr>: Document it. (AVR Pseudo Instructions): New node. * config/tc-avr.h (md_pre_output_hook): Define to avr_pre_output_hook. (md_undefined_symbol): Define to avr_undefined_symbol. (avr_pre_output_hook, avr_undefined_symbol): New protos. * config/tc-avr.c (struc-symbol.h): Include it. (ISR_CHUNK_Done, ISR_CHUNK_Prologue, ISR_CHUNK_Epilogue): New enums. (avr_isr, avr_gccisr_opcode) (avr_no_sreg_hash, avr_no_sreg): New static variables. (avr_opt_s) <have_gccisr>: Add field. (avr_opt): Add initializer for have_gccisr. (enum options) <OPTION_HAVE_GCCISR>: Add enum. (md_longopts) <"mgcc-isr">: Add entry. (md_show_usage): Document -mgcc-isr. (md_parse_option) [OPTION_HAVE_GCCISR]: Handle it. (md_undefined_symbol): Remove. (avr_undefined_symbol, avr_pre_output_hook): New fuctions. (md_begin) <avr_no_sreg_hash, avr_gccisr_opcode>: Initialize them. (avr_operand) <pregno>: Add argument and set *pregno if function is called for a register constraint. [N]: Handle constraint. (avr_operands) <avr_operand>: Pass 5th parameter to calls. [avr_opt.have_gccisr]: Call avr_update_gccisr. Call avr_gccisr_operands instead of avr_operands. (avr_update_gccisr, avr_emit_insn, avr_patch_gccisr_frag) (avr_gccisr_operands, avr_check_gccisr_done): New static functions. * testsuite/gas/avr/gccisr-01.d: New test. * testsuite/gas/avr/gccisr-01.s: New test. * testsuite/gas/avr/gccisr-02.d: New test. * testsuite/gas/avr/gccisr-02.s: New test. * testsuite/gas/avr/gccisr-03.d: New test. * testsuite/gas/avr/gccisr-03.s: New test.
Done.