Hi, on 2023/10/10 16:18, HAO CHEN GUI wrote: > Hi David, > > Thanks for your review comments. > > 在 2023/10/9 23:42, David Edelsohn 写道: >> #define MOVE_MAX (! TARGET_POWERPC64 ? 4 : 8) >> #define MAX_MOVE_MAX 8 >> +#define MOVE_MAX_PIECES (!TARGET_POWERPC64 ? 4 : 16) >> +#define COMPARE_MAX_PIECES (!TARGET_POWERPC64 ? 4 : 16) >> >> >> How are the definitions of MOVE_MAX_PIECES and COMPARE_MAX_PIECES >> determined? The email does not provide any explanation for the >> implementation. The rest of the patch is related to vector support, but >> vector support is not dependent on TARGET_POWERPC64. > > By default, MOVE_MAX_PIECES and COMPARE_MAX_PIECES is set the same value > as MOVE_MAX. The move and compare instructions are required in > compare_by_pieces, those macros are set to 16 byte when supporting > vector mode (V16QImode). The problem is rs6000 hasn't supported TImode > for "-m32". We discussed it in issue 1307. TImode will be used for > move when MOVE_MAX_PIECES is set to 16. But TImode isn't supported > with "-m32" which might cause ICE.
I think David raised a good question, it sounds to me that the current handling simply consider that if MOVE_MAX_PIECES is set to 16, the required operations for this optimization on TImode are always available, but unfortunately on rs6000 the assumption doesn't hold, so could we teach generic code instead? BR, Kewen
