On Mon, 17 Feb 2025, Richard Biener wrote:
> The following shows that tail-merging will make dead SSA defs live
> in paths where it wasn't before, possibly introducing UB or as
> in this case, uses of abnormals that eventually fail coalescing
> later. The fix is to register such defs for stmt comparison.
>
> Bootstrap and regtest running on x86_64-unknown-linux-gnu.
Pushed with the following additional testcase adjustment.
diff --git a/gcc/testsuite/gcc.dg/pr81192.c b/gcc/testsuite/gcc.dg/pr81192.c
index c46ac18fd9a..87a7a7a19c8 100644
--- a/gcc/testsuite/gcc.dg/pr81192.c
+++ b/gcc/testsuite/gcc.dg/pr81192.c
@@ -25,12 +25,16 @@ void __GIMPLE(ssa, startwith("pre")) fn2 ()
if (j_6(D) != _Literal (int)2147483647)
goto __BB4;
else
- goto __BB5;
+ goto __BB9;
__BB(4):
iftmp2_8 = j_6(D) + _Literal (int)1;
goto __BB5;
+ __BB(9):
+ iftmp2_8 = j_6(D) + _Literal (int)1;
+ goto __BB5;
+
__BB(5):
b_lsm6_10 = _Literal (int)2147483647;
goto __BB6;
> PR tree-optimization/98845
> * tree-ssa-tail-merge.cc (stmt_local_def): Consider a
> def with no uses not local.
>
> * gcc.dg/pr98845.c: New testcase.
> ---
> gcc/testsuite/gcc.dg/pr98845.c | 33 +++++++++++++++++++++++++++++++++
> gcc/tree-ssa-tail-merge.cc | 8 ++++++++
> 2 files changed, 41 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/pr98845.c
>
> diff --git a/gcc/testsuite/gcc.dg/pr98845.c b/gcc/testsuite/gcc.dg/pr98845.c
> new file mode 100644
> index 00000000000..074c979678f
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr98845.c
> @@ -0,0 +1,33 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fno-tree-dce -fno-tree-dse" } */
> +
> +int n;
> +
> +__attribute__ ((returns_twice)) void
> +foo (void);
> +
> +void
> +bar (void);
> +
> +void
> +quux (int x)
> +{
> + if (x)
> + ++x;
> + else
> + {
> + if (n)
> + {
> + x = 1;
> + foo ();
> + }
> + else
> + bar ();
> +
> + if (n)
> + {
> + ++x;
> + ++n;
> + }
> + }
> +}
> diff --git a/gcc/tree-ssa-tail-merge.cc b/gcc/tree-ssa-tail-merge.cc
> index d897970079c..857e91c206b 100644
> --- a/gcc/tree-ssa-tail-merge.cc
> +++ b/gcc/tree-ssa-tail-merge.cc
> @@ -336,10 +336,13 @@ stmt_local_def (gimple *stmt)
>
> def_bb = gimple_bb (stmt);
>
> + bool any_use = false;
> FOR_EACH_IMM_USE_FAST (use_p, iter, val)
> {
> if (is_gimple_debug (USE_STMT (use_p)))
> continue;
> +
> + any_use = true;
> bb = gimple_bb (USE_STMT (use_p));
> if (bb == def_bb)
> continue;
> @@ -351,6 +354,11 @@ stmt_local_def (gimple *stmt)
> return false;
> }
>
> + /* When there is no use avoid making the stmt live on other paths.
> + This can happen with DCE disabled or not done as seen in PR98845. */
> + if (!any_use)
> + return false;
> +
> return true;
> }
>
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
