Hi,
Richard Biener <rguent...@suse.de> writes: > On Fri, 9 Jun 2023, Jiufu Guo wrote: > >> >> Hi, >> >> Richard Biener <rguent...@suse.de> writes: >> >> > On Fri, 9 Jun 2023, Richard Sandiford wrote: >> > >> >> guojiufu <guoji...@linux.ibm.com> writes: >> >> > Hi, >> >> > >> >> > On 2023-06-09 16:00, Richard Biener wrote: >> >> >> On Fri, 9 Jun 2023, Jiufu Guo wrote: >> >> >> >> >> >>> Hi, >> >> >>> ... >> >> >>> >> >> >>> This patch is raised when drafting below one. >> >> >>> https://gcc.gnu.org/pipermail/gcc-patches/2022-October/603530.html. >> >> >>> With that patch, "{[%1:DI]=0;} stack_tie" with BLKmode runs into >> >> >>> try_const_anchors, and hits the assert/ice. >> >> >>> >> >> >>> Boostrap and regtest pass on ppc64{,le} and x86_64. >> >> >>> Is this ok for trunk? >> >> >> >> >> >> Iff the correct fix at all (how can a CONST_INT have BLKmode?) then >> >> >> I suggest to instead fix try_const_anchors to change >> >> >> >> >> >> /* CONST_INT is used for CC modes, but we should leave those alone. >> >> >> */ >> >> >> if (GET_MODE_CLASS (mode) == MODE_CC) >> >> >> return NULL_RTX; >> >> >> >> >> >> gcc_assert (SCALAR_INT_MODE_P (mode)); >> >> >> >> >> >> to >> >> >> >> >> >> /* CONST_INT is used for CC modes, leave any non-scalar-int mode >> >> >> alone. */ >> >> >> if (!SCALAR_INT_MODE_P (mode)) >> >> >> return NULL_RTX; >> >> >> >> >> > >> >> > This is also able to fix this issue. there is a "Punt on CC modes" >> >> > patch >> >> > to return NULL_RTX in try_const_anchors. >> >> > >> >> >> but as said I wonder how we arrive at a BLKmode CONST_INT and whether >> >> >> we should have fended this off earlier. Can you share more complete >> >> >> RTL of that stack_tie? >> >> > >> >> > >> >> > (insn 15 14 16 3 (parallel [ >> >> > (set (mem/c:BLK (reg/f:DI 1 1) [1 A8]) >> >> > (const_int 0 [0])) >> >> > ]) "/home/guojiufu/temp/gdb.c":13:3 922 {stack_tie} >> >> > (nil)) >> >> > >> >> > It is "set (mem/c:BLK (reg/f:DI 1 1) (const_int 0 [0])". >> >> >> >> I'm not convinced this is correct RTL. (unspec:BLK [(const_int 0)] ...) >> >> would be though. It's arguably more accurate too, since the effect >> >> on the stack locations is unspecified rather than predictable. >> > >> > powerpc seems to be the only port with a stack_tie that's not >> > using an UNSPEC RHS. >> In rs6000.md, it is >> >> ; This is to explain that changes to the stack pointer should >> ; not be moved over loads from or stores to stack memory. >> (define_insn "stack_tie" >> [(match_parallel 0 "tie_operand" >> [(set (mem:BLK (reg 1)) (const_int 0))])] >> "" >> "" >> [(set_attr "length" "0")]) >> >> This would be just an placeholder insn, and acts as the comments. >> UNSPEC_ would works like other targets. While, I'm wondering >> the concerns on "set (mem:BLK (reg 1)) (const_int 0)". >> MODEs between SET_DEST and SET_SRC? > > I don't think the issue is the mode but the issue is that > the patter as-is says some memory is zeroed while that's not > actually true (not specifying a size means we can't really do > anything with this MEM, but still). Using an UNSPEC avoids > implying anything for the stored value. > > Of course I think a MEM SET_DEST without a specified size is bougs > as well, but there's larger precedent for this... Thanks for your kindly comments! Using "(set (mem:BLK (reg 1)) (const_int 0))" here, may because this insn does not generate real thing (not a real store and no asm code), may like barrier. While I agree that, using UNSPEC may be more clear to avoid mis-reading. BR, Jeff (Jiufu Guo) > > Richard. > >> Thanks for comments! >> >> BR, >> Jeff (Jiufu Guo) >> > >> >> Thanks, >> >> Richard >>
