On Fri, Jun 5, 2026 at 7:43 AM Andrew Pinski
<[email protected]> wrote:
>
> r17-1273-g391ee229b737eb added support for the case where the middle bb was
> non-empty but
> with a trailing store. This meant if there was a load in the middle bb, it
> might cause
> nontrapping to have the lhs in it. So we now need to check for a load in the
> middle-bb
> to reject this case.
>
> Bootstrapped and tested on x86_64-linux-gnu.
>
> PR tree-optimization/125612
>
> gcc/ChangeLog:
>
> * tree-ssa-phiopt.cc (cond_store_replacement): For the case where
> lhs is "known" to be nontrapping make sure there are no loads in
> the middle bb.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/pr125612-1.c: New test.
>
> Signed-off-by: Andrew Pinski <[email protected]>
> ---
> gcc/testsuite/gcc.dg/tree-ssa/pr125612-1.c | 26 ++++++++++++++++++++++
> gcc/tree-ssa-phiopt.cc | 19 +++++++++++++++-
> 2 files changed, 44 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr125612-1.c
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr125612-1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr125612-1.c
> new file mode 100644
> index 00000000000..201f2f4fb3f
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr125612-1.c
> @@ -0,0 +1,26 @@
> +/* { dg-do run } */
> +/* { dg-options "-O3 -fno-tree-dse -fno-tree-dce -fdump-tree-cselim-details"
> } */
> +/* PR tree-optimization/125612 */
> +
> +/* The conditional store of `h[2000]` should not become unconditional since
> + it traps. */
> +
> +int a, b, c = 2, d, e[4], f, i;
> +void g() {
> + int h[5];
> + e[0] = 2;
> + while (1) {
> + if (e[b]) {
> + if (!c)
> + h[2000] &= 1;
> + return;
> + }
> + }
> +}
> +int main() {
> + for (; i < 4; i++)
> + g();
> + return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump-not "Conditional store replacement happened"
> "cselim"} } */
> diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
> index 3e7dd3b0ee3..0c5c4982d3f 100644
> --- a/gcc/tree-ssa-phiopt.cc
> +++ b/gcc/tree-ssa-phiopt.cc
> @@ -3089,7 +3089,24 @@ cond_store_replacement (basic_block middle_bb,
> basic_block join_bb, edge e0,
> /* Prove that we can move the store down. We could also check
> TREE_THIS_NOTRAP here, but in that case we also could move stores,
> whose value is not available readily, which we want to avoid. */
> - if (!nontrap->contains (lhs))
> + if (nontrap->contains (lhs))
> + {
> + /* Make sure there is no load in the middle bb,
> + this invalidates nontrap.
How so? nontrap should only contain the load, not the store? We mark
a MEM as not trapping if there's a dominating same MEM only and
nontrap contains the actual tree (which is always unshared)
> + FIXME: this is over conserative, this check could be made to
> + allow loads unrelated to lhs. */
> + tree vuse = gimple_vuse (assign);
> + imm_use_iterator iter;
> + gimple *use_stmt;
> + FOR_EACH_IMM_USE_STMT (use_stmt, iter, vuse)
> + {
> + if (use_stmt == assign)
> + continue;
> + if (gimple_bb (use_stmt) == middle_bb)
> + return false;
> + }
> + }
> + else
> {
> /* If LHS is an access to a local variable without address-taken
> (or when we allow data races) and known not to trap, we could
> --
> 2.43.0
>
