Denis Chertykov schrieb: > 2011/4/17 Denis Chertykov <cherty...@gmail.com>: >> 2011/4/15 Georg-Johann Lay <a...@gjlay.de>: >>> Finally, I exposed alternative #3 of the insns to the register >>> allocator, because it is not possible to distinguish between >>> overlapping or non-overlapping regs, and #3 does not need a scratch. >>> >>> Ran C-testsuite with no regressions. >> Are you encountered any difference in code size ? > > I'm ask about code size because the IRA pass isn't work with > `scratch:MODE' at all.
I wonder what the difference is; IRA could treat scratch:MODE just the same way as pseudo:MODE. Anyway, thanks for that insight. It's merely impossible to get the big picture of IRA/reload from digging sources. So that means IRA generates garbage for scratch and reload has to fix it, generate spill code if needed, etc? Does this mean that if IRA sees a pseudo together with constraint "X" it will allocate the pseudo, anyway? > This lead to bad/wrong register allocation in IRA pass. > The reload pass will correct such a wrong allocation, but reload can't > generate optimal code. (reload generate correct code). > Because of that, may be you right and may be better to have > (clobber (match_operand....)) instead of (clobber (match_scratch...)). I don't see effects on code size, at least for the binaries left by testsuite. Is there a policy how to drive size-performance tests for avr? Anatoly posted a result on code size some weeks ago (concerning move costs), it would be interesting to know his setup and what sources/options he uses. Using testsuite seems not appropriate to me, because it runs -O3, -finline etc. and most code is no real-world code, at least not for avr. FYI, what I observe is a remarkable dependency on subreg lowering that can be generalized as this: * code size decreases for mode <= SImode * code size increases for mode > SImode An example for gcc.target/avr/torture/pr41885.c -Os -fno-split-wide-types 00000000 00000008 T rotl_16a 00000008 00000006 T rotl_16b 00000014 00000012 T rotl_32a 00000026 00000010 T rotl_32b 00000036 00000006 T rotl_32c 00000042 00000010 T rotl_32d 00000052 00000010 T rotl_32e 00000062 00000088 T rotl_64 00000150 00000106 T rotl_64a 00000256 00000082 T rotl_64b 00000338 00000096 T rotl_64c 00000434 00000098 T rotl_64d 00000532 00000100 T rotl_64e 00000632 00000102 T rotl_64f 00000734 00000104 T rotl_64g 00000838 00000110 T rotl_64h -fsplit-wide-types 00000000 00000008 T rotl_16a 00000008 00000006 T rotl_16b 00000014 00000024 T rotl_32a 00000038 00000020 T rotl_32b 00000058 00000024 T rotl_32c 00000082 00000022 T rotl_32d 00000104 00000022 T rotl_32e 00000126 00000036 T rotl_64 00000162 00000050 T rotl_64a 00000212 00000026 T rotl_64b 00000238 00000036 T rotl_64c 00000274 00000038 T rotl_64d 00000312 00000040 T rotl_64e 00000352 00000042 T rotl_64f 00000394 00000044 T rotl_64g 00000438 00000038 T rotl_64h Johann > > Denis. >
