Le 03/05/2012 14:14, Aurelien Buhrig a écrit : > 02/05/2012 21:36, Eric Botcazou : >>> I have an issue (gcc 4.6.3, private bacakend) when reloading operands of >>> this insn: >>> (set (subreg:SI (reg:QI 21 [ iftmp.1 ]) 0) >>> (lshiftrt:SI (reg/v:SI 24 [ w ]) (const_int 31 [0x1f])) >>> >>> The register 21 is reloaded into >>> (reg:QI 0 r0 [orig:21 iftmp.1 ] [21]), which is a HI-wide hw register. >>> Since it is a BIG_ENDIAN target, the SI subreg regno is then -1. >>> >>> Note that word_mode is SImode, whereas the class r0 belongs to is >>> HI-wide. I don't know if this matters when reloading. >>> >>> I have no idea how to debug this, if it is a backend or a reload bug. >> >> RA/reload is known to have issues with word-mode paradoxical subregs on >> big-endian machines. For example, on SPARC 64-bit, we run into similar >> problems for FP regs, which are 32-bit. Likewise on HP-PA 64-bit I think. >> >> So we have kludges in the back-end: >> >> /* Defines invalid mode changes. Borrowed from the PA port. >> >> SImode loads to floating-point registers are not zero-extended. >> The definition for LOAD_EXTEND_OP specifies that integer loads >> narrower than BITS_PER_WORD will be zero-extended. As a result, >> we inhibit changes from SImode unless they are to a mode that is >> identical in size. >> >> Likewise for SFmode, since word-mode paradoxical subregs are >> problematic on big-endian architectures. */ >> >> #define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \ >> (TARGET_ARCH64 \ >> && GET_MODE_SIZE (FROM) == 4 \ >> && GET_MODE_SIZE (TO) != 4 \ >> ? reg_classes_intersect_p (CLASS, FP_REGS) : 0) >> > > > I modified CANNOT_CHANGE_MODE_CLASS as you suggested. But strange as it > may seem, it has no effect on such a reload, and I can't find a way to > make it work... > > BTW, has this bug already been filed? > Do you have an idea how deep is this bug in the reload, how complex it > is and which part in the reload it is related to? > > Thanks, > Aurélien
It seems the paradoxical subreg information is not available from ira_allocno_t nor ira_object_t when choosing the hw reg. I finally changed word_mode to the smallest hw reg size (HImode) to work around this bug. Aurélien
