https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105769
--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #9)
> And just statements that refer to those 3 variables that (incorrectly) share
> the stack slot + basic block boundaries.
> grep 'bias\|D.5698\|D.5681\|:' /tmp/00
> struct struct void D.5698;
> struct map_t D.5681;
> struct vec bias;
> <bb 2> [local count: 1073741829]:
> _12 = (long unsigned int) &bias;
> bias ={v} {CLOBBER};
> __ct_comp (&D.5698.__est, &D.5682);
> <bb 3> [local count: 1073741824]:
> MEM <vector(2) long unsigned int> [(void *)&D.5698 + 32B] = _21;
> <bb 4> [local count: 1073741824]:
> __ct_comp (_14, &D.5698.__est);
> <bb 5> [local count: 1073741824]:
> vect__16.52_79 = MEM <vector(2) long unsigned int> [(void *)&D.5698 + 32B];
> __dt_base (&MEM[(struct function *)&D.5698].D.5235);
> D.5698 ={v} {CLOBBER};
> D.5698 ={v} {CLOBBER(eol)};
> MEM <char[16]> [(struct _Function_base *)&D.5681] = {};
> MEM <vector(2) long unsigned int> [(bool (*<T72d>) (union _Any_data &
> {ref-all}, const union _Any_data & {ref-all}, _Manager_operation) *)&D.5681
> + 16B] = _84;
> <bb 6> [count: 0]:
> <L5>:
> <bb 7> [count: 0]:
> <L4>:
> __dt_base (&MEM[(struct function *)&D.5698].D.5235);
> D.5698 ={v} {CLOBBER};
> <bb 8> [local count: 429496]:
> <bb 9> [local count: 1073312328]:
> _19 (&D.5683.D.5217._M_functor, &D.5681);
> <bb 10> [local count: 1073312328]:
> __dt_base (&D.5681.D.5223);
> D.5681 ={v} {CLOBBER};
> D.5681 ={v} {CLOBBER(eol)};
> bias ={v} {CLOBBER(eol)};
> <bb 11> [count: 0]:
> <L0>:
> __dt_base (&D.5681.D.5223);
> D.5681 ={v} {CLOBBER};
> D.5681 ={v} {CLOBBER(eol)};
> <bb 12> [count: 0]:
> <L2>:
> D.5698 ={v} {CLOBBER};
>
> Now, perhaps the sharing of stack slot between D.5681 and D.5698 is fine,
> seems
> D.5698 is destructed before D.5681 is constructed:
> D.5698 ={v} {CLOBBER};
> D.5698 ={v} {CLOBBER(eol)};
> MEM <char[16]> [(struct _Function_base *)&D.5681] = {};
> and D.5698 is later used just in EH block reachable only from earlier basic
> blocks
> or just as
> D.5698 ={v} {CLOBBER};
> in the last EH bb. But the sharing of the stack slot in between bias and
> D.5698 looks wrong. What can be seen in the IL is:
> _12 = (long unsigned int) &bias;
> which has been hoisted before the
> bias ={v} {CLOBBER};
> statement by the slp1 pass.
> From:
> ;; basic block 2, loop depth 0
> ;; pred: ENTRY
> _3 = operator<< (&cout, "will do (ab)");
> endl (_3);
> MEM[(struct vec *)&cov_jn] ={v} {CLOBBER};
> bias ={v} {CLOBBER};
> MEM[(struct function *)&D.5682] ={v} {CLOBBER};
> MEM <char[16]> [(struct _Function_base *)&D.5682] = {};
> MEM[(struct function *)&D.5682]._M_invoker = _M_invoke;
> MEM[(struct function *)&D.5682].D.5235._M_manager = _M_manager;
> __ct_comp (&D.5698.__est, &D.5682);
> ;; succ: 5
> ;; 18
>
> ;; basic block 5, loop depth 0
> ;; pred: 2
> D.5698.__cov = &cov_jn;
> D.5698.__bias = &bias;
> in dse4 to:
> ;; basic block 2, loop depth 0
> ;; pred: ENTRY
> _12 = VIEW_CONVERT_EXPR<long unsigned int>(&bias);
> _15 = VIEW_CONVERT_EXPR<long unsigned int>(&cov_jn);
> _21 = {_15, _12};
> _9 = VIEW_CONVERT_EXPR<long unsigned int>(_M_invoke);
> _10 = VIEW_CONVERT_EXPR<long unsigned int>(_M_manager);
> _8 = {_10, _9};
> _3 = operator<< (&cout, "will do (ab)");
> endl (_3);
> MEM[(struct vec *)&cov_jn] ={v} {CLOBBER};
> bias ={v} {CLOBBER};
> MEM[(struct function *)&D.5682] ={v} {CLOBBER};
> MEM <char[16]> [(struct _Function_base *)&D.5682] = {};
> MEM <vector(2) long unsigned int> [(bool (*<T72d>) (union _Any_data &
> {ref-all}, const union _Any_data & {ref-all}, _Manager_operation) *)&D.5682
> + 16B] = _8;
> __ct_comp (&D.5698.__est, &D.5682);
> ;; succ: 5
> ;; 18
>
> ;; basic block 5, loop depth 0
> ;; pred: 2
> MEM <vector(2) long unsigned int> [(void *)&D.5698 + 32B] = _21;
> in slp1.
>
> Is that what is incorrect? And we should never hoist taking of addresses
> before a clobber on that var?
I think that's the usual pattern for the two other stack-slot sharing PRs we
have. The liveness analysis makes wrong assumptions about CLOBBER and CLOBBER
isn't a barrier for address-takens (and we don't have birth CLOBBERs).
But why does -fstack-reuse=none not help?
