On Wed, 19 Nov 2025, Jakub Jelinek wrote:
> Hi!
>
> remove_unused_locals ignores clobbers in the initial phase (and
> some debug stmts) and this has been copied for .DEFERRED_INIT
> as well:
> if (gimple_clobber_p (stmt))
> {
> have_local_clobbers = true;
> continue;
> }
>
> if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
> {
> have_local_clobbers = true;
> continue;
> }
> This is so that the second phase can then drop clobbers that
> clobber unused local vars and ditto for .DEFERRED_INIT.
> Except, for clobbers it does
> /* Remove clobbers referencing unused vars, or clobbers
> with MEM_REF lhs referencing uninitialized pointers. */
> if ((VAR_P (base) && !is_used_p (base))
> || (TREE_CODE (lhs) == MEM_REF
> && TREE_CODE (TREE_OPERAND (lhs, 0)) == SSA_NAME
> && SSA_NAME_IS_DEFAULT_DEF (TREE_OPERAND (lhs, 0))
> && (TREE_CODE (SSA_NAME_VAR (TREE_OPERAND (lhs, 0)))
> != PARM_DECL)))
> so handles both the var = {CLOBBER}; case where var is unused local,
> or *SSA_NAME = {CLOBBER} where SSA_NAME is default definition of
> non-PARM_DECL, but for .DEFERRED_INIT it doesn't:
> if (DECL_P (base) && !is_used_p (base))
> On the following case, we have *SSA_NAME(D) = .DEFERRED_INIT (...);
> and because of the former we don't mark the SSA_NAME as used and
> because of the latter we keep the .DEFERRED_INIT call, so the SSA_NAME
> is freed and later on we ICE because the SSA_NAME in the freelist doesn't
> have SSA_NAME_DEF_STMT.
>
> The following patch fixes it by handling .DEFERRED_INIT like clobbers
> and dropping them also when it has a MEM_REF with default definition
> of SSA_NAME for non-PARM_DECL on the lhs.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Thanks,
Richard.
> 2025-11-19 Jakub Jelinek <[email protected]>
>
> PR tree-optimization/122184
> * tree-ssa-live.cc (remove_unused_locals): Drop .DEFERRED_INIT
> calls with MEM_REF lhs based on uninitialized SSA_NAME.
>
> * g++.dg/opt/pr122184-1.C: New test.
> * g++.dg/opt/pr122184-2.C: New test.
>
> --- gcc/tree-ssa-live.cc.jj 2025-07-07 11:04:58.566699746 +0200
> +++ gcc/tree-ssa-live.cc 2025-11-18 13:43:26.938709025 +0100
> @@ -926,7 +926,12 @@ remove_unused_locals (void)
> {
> tree lhs = gimple_call_lhs (stmt);
> tree base = get_base_address (lhs);
> - if (DECL_P (base) && !is_used_p (base))
> + if ((DECL_P (base) && !is_used_p (base))
> + || (TREE_CODE (lhs) == MEM_REF
> + && TREE_CODE (TREE_OPERAND (lhs, 0)) == SSA_NAME
> + && SSA_NAME_IS_DEFAULT_DEF (TREE_OPERAND (lhs, 0))
> + && (TREE_CODE (SSA_NAME_VAR (TREE_OPERAND (lhs, 0)))
> + != PARM_DECL)))
> {
> unlink_stmt_vdef (stmt);
> gsi_remove (&gsi, true);
> --- gcc/testsuite/g++.dg/opt/pr122184-1.C.jj 2025-11-18 13:50:16.496894332
> +0100
> +++ gcc/testsuite/g++.dg/opt/pr122184-1.C 2025-11-18 13:49:42.515376787
> +0100
> @@ -0,0 +1,12 @@
> +// PR tree-optimization/122184
> +// { dg-do compile }
> +// { dg-require-stack-check "generic" }
> +// { dg-options "-O2 -fstack-check=generic" }
> +
> +void
> +foo ()
> +{
> + goto fail;
> + char var[41];
> +fail:;
> +}
> --- gcc/testsuite/g++.dg/opt/pr122184-2.C.jj 2025-11-18 14:18:10.642137383
> +0100
> +++ gcc/testsuite/g++.dg/opt/pr122184-2.C 2025-11-18 14:18:30.539854977
> +0100
> @@ -0,0 +1,12 @@
> +// PR tree-optimization/122184
> +// { dg-do compile }
> +// { dg-require-stack-check "generic" }
> +// { dg-options "-O2 -fstack-check=generic -ftrivial-auto-var-init=zero" }
> +
> +void
> +foo ()
> +{
> + goto fail;
> + char var[41];
> +fail:;
> +}
>
> Jakub
>
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
