[gcc r13-10028] isel: Check bounds before converting VIEW_CONVERT to VEC_SET.

[Avinash Jayakar]

https://gcc.gnu.org/g:0fe9607591c911d1f6b807e5353a1e1a99d249ca

commit r13-10028-g0fe9607591c911d1f6b807e5353a1e1a99d249ca
Author: Avinash Jayakar <avinashd@linux.ibm.com>
Date:   Sat Nov 8 09:57:59 2025 +0530

    isel: Check bounds before converting VIEW_CONVERT to VEC_SET.
    
    The function gimple_expand_vec_set_expr in the isel pass, converted
    VIEW_CONVERT_EXPR to VEC_SET_EXPR without checking the bounds on the index,
    which cause ICE on targets that supported VEC_SET_EXPR like x86 and powerpc.
    This patch adds a bound check on the index operand and rejects the conversion
    if index is out of bound.
    
    2026-01-05  Avinash Jayakar  <avinashd@linux.ibm.com>
    
    gcc/ChangeLog:
            PR tree-optimization/122126
            * gimple-isel.cc (gimple_expand_vec_set_extract_expr): Add bound check.
    
    gcc/testsuite/ChangeLog:
            PR tree-optimization/122126
            * gcc.dg/pr122126_vextr.c: New test.
            * gcc.dg/pr122126_vset.c: New test.

Diff:
---
 gcc/gimple-isel.cc                    | 9 +++++++++
 gcc/testsuite/gcc.dg/pr122126_vextr.c | 9 +++++++++
 gcc/testsuite/gcc.dg/pr122126_vset.c  | 9 +++++++++
 3 files changed, 27 insertions(+)

diff --git a/gcc/gimple-isel.cc b/gcc/gimple-isel.cc
index 760029d27c97..f7eabeca6475 100644
--- a/gcc/gimple-isel.cc
+++ b/gcc/gimple-isel.cc
@@ -76,6 +76,15 @@ gimple_expand_vec_set_expr (struct function *fun, gimple_stmt_iterator *gsi)
     {
       tree pos = TREE_OPERAND (lhs, 1);
       tree view_op0 = TREE_OPERAND (op0, 0);
+
+      // if index is a constant, then check the bounds
+      poly_uint64 idx_poly;
+      if (poly_int_tree_p (pos, &idx_poly))
+	{
+	  poly_uint64 nelts = TYPE_VECTOR_SUBPARTS (TREE_TYPE (view_op0));
+	  if (known_gt (idx_poly, nelts))
+	    return false;
+	}
       machine_mode outermode = TYPE_MODE (TREE_TYPE (view_op0));
       if ((auto_var_in_fn_p (view_op0, fun->decl)
 	   || (VAR_P (view_op0) && DECL_HARD_REGISTER (view_op0)))
diff --git a/gcc/testsuite/gcc.dg/pr122126_vextr.c b/gcc/testsuite/gcc.dg/pr122126_vextr.c
new file mode 100644
index 000000000000..b598aa01091d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr122126_vextr.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-additional-options "-mavx2" { target avx2 } } */
+
+#define vect16 __attribute__((vector_size(16)))
+void ub_set() {
+  volatile vect16 unsigned BS_VAR_0;
+  unsigned a = BS_VAR_0[12];
+}
diff --git a/gcc/testsuite/gcc.dg/pr122126_vset.c b/gcc/testsuite/gcc.dg/pr122126_vset.c
new file mode 100644
index 000000000000..85b2c68247b6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr122126_vset.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-additional-options "-mavx2" { target avx2 } } */
+
+#define vect16 __attribute__((vector_size(16)))
+void ub_set() {
+  volatile vect16 unsigned BS_VAR_0;
+  BS_VAR_0[12] = 4;
+}