| Message ID | mpt7e9fm4vm.fsf@arm.com |
|---|---|
| State | New |
| Headers | show |
| Series | Tweak IRA handling of tying and earlyclobbers | expand |
On 2019-06-21 9:42 a.m., Richard Sandiford wrote: > ira_get_dup_out_num punted on operands that are matched to > earlyclobber outputs: > > /* It is better ignore an alternative with early clobber. */ > else if (*str == '&') > goto fail; > > But I'm not sure why this is the right thing to do. At this stage > we've established that *all* alternatives of interest require the > input to match the output, so > > (a) the earlyclobber can only affect other operands and > (b) not tying the registers is bound to introduce a move > > The code was part of the initial commit and so isn't obviously > related to a specific testcase. Also, I can imagine LRA makes > a much better job of this situation than reload did. (Certainly > SVE uses matched earlyclobbers extensively and I haven't seen any > problems.) I don't remember the reason for this either as the code is more 10 years old. I can only speculate that this approach was influenced by the old RA (global.c). I remember that it processed earlyclobber registers too but may be in a different way. > In case this turns out to regress something important: the main > case that matters for SVE is the one in which all alternatives > are earlyclobber. > OK to commit. > 2019-06-21 Richard Sandiford <richard.sandiford@arm.com> > > gcc/ > * ira.c (ira_get_dup_out_num): Don't punt for earlyclobbers. > Use recog_data to test for an output operand. > > Index: gcc/ira.c > =================================================================== > --- gcc/ira.c 2019-06-21 14:34:13.239653892 +0100 > +++ gcc/ira.c 2019-06-21 14:34:15.947631377 +0100 > @@ -1999,26 +1999,8 @@ ira_get_dup_out_num (int op_num, alterna > } > if (original == -1) > goto fail; > - dup = -1; > - for (ignore_p = false, str = recog_data.constraints[original - '0']; > - *str != 0; > - str++) > - if (ignore_p) > - { > - if (*str == ',') > - ignore_p = false; > - } > - else if (*str == '#') > - ignore_p = true; > - else if (! ignore_p) > - { > - if (*str == '=') > - dup = original - '0'; > - /* It is better ignore an alternative with early clobber. */ > - else if (*str == '&') > - goto fail; > - } > - if (dup >= 0) > + dup = original - '0'; > + if (recog_data.operand_type[dup] == OP_OUT) > return dup; > fail: > if (use_commut_op_p)
Index: gcc/ira.c =================================================================== --- gcc/ira.c 2019-06-21 14:34:13.239653892 +0100 +++ gcc/ira.c 2019-06-21 14:34:15.947631377 +0100 @@ -1999,26 +1999,8 @@ ira_get_dup_out_num (int op_num, alterna } if (original == -1) goto fail; - dup = -1; - for (ignore_p = false, str = recog_data.constraints[original - '0']; - *str != 0; - str++) - if (ignore_p) - { - if (*str == ',') - ignore_p = false; - } - else if (*str == '#') - ignore_p = true; - else if (! ignore_p) - { - if (*str == '=') - dup = original - '0'; - /* It is better ignore an alternative with early clobber. */ - else if (*str == '&') - goto fail; - } - if (dup >= 0) + dup = original - '0'; + if (recog_data.operand_type[dup] == OP_OUT) return dup; fail: if (use_commut_op_p)