On Fri, 9 Jun 2023, Jiufu Guo wrote: > > 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.
Btw, another way to avoid the issue in CSE is to make it not process (aka record anything for optimization) for SET from MEMs with !MEM_SIZE_KNOWN_P Richard.
