2015-12-16 10:08 GMT+03:00 Senthil Kumar Selvaraj <senthil_kumar.selva...@atmel.com>: > Hi, > > When analyzing code size regressions for AVR for top-of-trunk, I > found a few cases where aggresive inlining (by the middle-end) > of functions containing calls to memcpy was bloating up the code. > > Turns out that the AVR backend has MOVE_MAX set to 4 (unchanged from the > original commit), when it really should be 1, as the AVRs can only > move a single byte between reg and memory in a single instruction. > Setting it to 4 causes the middle end to underestimate the > cost of memcopys with a compile time constant length parameter, as it > thinks a 4 byte copy's cost is only a single instruction. > > Just setting MOVE_MAX to 1 makes the middle end too conservative > though, and causes a bunch of regression tests to fail, as lots of > optimizations fail to pass the code size increase threshold check, > even when not optimizing for size. > > Instead, the below patch sets MOVE_MAX_PIECES to 2, and implements a > target hook that tells the middle-end to use load/store insns for > memory moves upto two bytes. Also, the patch sets MOVE_RATIO to 3 when > optimizing for speed, so that moves upto 4 bytes will occur through > load/store sequences, like it does now. > > With this, only a couple of regression tests fail. uninit-19.c fails > because it thinks only non-pic code won't inline a function, but the > cost computation prevents inlining for AVRs. The test passes if > the optimization level is increased to -O3. > > strlenopt-8.c has an XPASS and a FAIL because a previous pass issued > a builtin_memcpy instead of a MEM assignment. Execution still passes. > > I'll continue running more tests to see if there are other performance > related consequences. > > Is this ok? If ok, could someone commit please? I don't have commit > access. > > Regards > Senthil > > gcc/ChangeLog > > 2015-12-16 Senthil Kumar Selvaraj <senthil_kumar.selva...@atmel.com> > > * config/avr/avr.h (MOVE_MAX): Set value to 1. > (MOVE_MAX_PIECES): Define. > (MOVE_RATIO): Define. > * config/avr/avr.c (TARGET_USE_BY_PIECES_INFRASTRUCTURE_P): > Provide target hook. > (avr_use_by_pieces_infrastructure_p): New function.
Committed. Denis.
