Re: [patch] Fix non-standard Ada bootstrap failure on IA-64

[Richard Guenther <richard dot guenther at gmail dot com>]

On Tue, Mar 6, 2012 at 11:08 PM, Eric Botcazou <ebotcazou@adacore.com> wrote:
> If you try to bootstrap the GNAT 4.7.0 compiler on IA-64/Linux with non-default
> options (-gnatpg replaced with -gnatpgn), you get another comparison failure
> caused by debug insns, stemming from the machine-specific reorg pass (aka insn
> bundling on IA-64). ?With -g , when cselib is called on:
>
> (insn 17 41 18 2 (set (reg/f:DI 14 r14 [357])
> ? ? ? ?(plus:DI (reg:DI 16 r16 [356])
> ? ? ? ? ? ?(const_int 28
> [0x1c]))) /home/eric/gnat.b/gnat7_47/src/gcc/ada/atree.adb:2244 205 {adddi3}
> ? ? (expr_list:REG_DEAD (reg:DI 16 r16 [356])
> ? ? ? ?(nil)))
>
> it finds a previous equivalent value:
>
> (plus:DI (plus:DI (ashift:DI (value:DI 5:111 @0x29abbe0/0x29f5f20)
> ? ? ? ? ? ?(const_int 5 [0x5]))
> ? ? ? ?(value:DI 9:9 @0x29abc40/0x29f5fe0))
> ? ?(const_int 28 [0x1c]))
>
> computed for a debug insn:
>
> (debug_insn 12 10 65 2 (var_location:SI n (mem/j:SI (plus:DI (plus:DI
> (ashift:DI (reg:DI 14 r14 [orig:344 D.2979 ] [344])
> ? ? ? ? ? ? ? ? ? ?(const_int 5 [0x5]))
> ? ? ? ? ? ? ? ?(reg/f:DI 15 r15 [orig:342
> atree__atree_private_part__nodes__table.32 ] [342]))
> ? ? ? ? ? ?(const_int 28 [0x1c])) [0
> *atree__atree_private_part__nodes__table.32_17
> [D.2979_19].is_extension___XVN.S0.field5+0 S4 A8])) sem_ch2.adb:49 -1
> ? ? (nil))
>
> When output_dependence is called on a couple of MEMs, it uses the above value
> to get the equivalent addresses:
>
> (plus:DI (value:DI 9:9 @0x29abc40/0x29f5fe0)
> ? ?(value:DI 12:4189 @0x29abc88/0x29c8a20))
>
> and
>
> (plus:DI (plus:DI (ashift:DI (value:DI 5:111 @0x29abbe0/0x29f5f20)
> ? ? ? ? ? ?(const_int 5 [0x5]))
> ? ? ? ?(value:DI 9:9 @0x29abc40/0x29f5fe0))
> ? ?(const_int 28 [0x1c]))
>
> and rtx_refs_may_alias_p returns true on them because ao_ref_from_mem returns
> false for one of the MEMs.
>
>
> Without -g, when cselib is called on:
>
> (insn 14 30 15 2 (set (reg/f:DI 14 r14 [357])
> ? ? ? ?(plus:DI (reg:DI 16 r16 [356])
> ? ? ? ? ? ?(const_int 28
> [0x1c]))) /home/eric/gnat.b/gnat7_47/src/gcc/ada/atree.adb:2244 205 {adddi3}
> ? ? (expr_list:REG_DEAD (reg:DI 16 r16 [356])
> ? ? ? ?(nil)))
>
> output_dependence only gets the equivalent addresses:
>
> (plus:DI (value:DI 8:8 @0x299f2e8/0x299f1a0)
> ? ?(value:DI 10:4188 @0x299f318/0x299f200))
>
> and
>
> (plus:DI (value:DI 12:4254 @0x299f348/0x29a0490)
> ? ?(const_int 28 [0x1c]))
>
> and memrefs_conflict_p is able to prove that they don't conflict.
>
>
> The problem is that the more complex expression in the first case fools
> memrefs_conflict_p because the predicate makes a wrong assumption about the
> canonicalization of address expressions. ?Hence the attached patch.
>
> Bootstrapped/regtested on IA-64/Linux, OK for the mainline? ?Do we also want it
> for 4.7.1 or is it too specific?

Hmm, but isn't the bug that we feed debug-insn mems to memrefs_conflict_p?
Or that we have non-legitimate address expressions in them?

Richard.

>
> 2012-03-06 ?Eric Botcazou ?<ebotcazou@adacore.com>
>
> ? ? ? ?* alias.c (memrefs_conflict_p) <PLUS>: Correct wrong assumption about
> ? ? ? ?canonicalization of address expressions.
>
>
> --
> Eric Botcazou