[gcc r17-2881] phiopt: Factor loads, reject if the pointer types are not compatiable [PR126571]

https://gcc.gnu.org/g:7f83719c13e9c8521a08ecba4cb8e3a6f6f48e2d

commit r17-2881-g7f83719c13e9c8521a08ecba4cb8e3a6f6f48e2d
Author: Andrea Pinski <[email protected]>
Date:   Sat Aug 1 16:17:25 2026 -0700

    phiopt: Factor loads, reject if the pointer types are not compatiable [PR126571]
    
    In some cases (different address space and/or function pointers) pointers are considered
    non-compatible. This means creating a phi with non-compatible pointers will fail.
    This takes the easy way out and rejecting this case. This could be refined to support
    the only case where address spaces are different but that case will show up much less
    than the address space being different so it is not worth the trouble right now.
    
    Pushed as obvious after bootstrap/test on x86_64-linux-gnu.
    
            PR tree-optimization/126571
    
    gcc/ChangeLog:
    
            * tree-ssa-phiopt.cc (factor_out_conditional_load): Reject
            when the pointer types are not compatible when creating a phi.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/torture/pr126571-1.c: New test.
            * gcc.target/i386/pr126571-1.c: New test.
    
    Signed-off-by: Andrea Pinski <[email protected]>

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr126571-1.c  | 14 ++++++++++++++
 gcc/testsuite/gcc.target/i386/pr126571-1.c | 16 ++++++++++++++++
 gcc/tree-ssa-phiopt.cc                     |  3 +++
 3 files changed, 33 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/torture/pr126571-1.c b/gcc/testsuite/gcc.dg/torture/pr126571-1.c
new file mode 100644
index 000000000000..573972d88ba8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr126571-1.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* PR tree-optimization/126571 */
+typedef void (*FP) (void);
+
+int
+f (int c, FP fp, int *q)
+{
+  int r;
+  if (c)
+    r = *(int *) fp;
+  else
+    r = *q;
+  return r + 1;
+}
diff --git a/gcc/testsuite/gcc.target/i386/pr126571-1.c b/gcc/testsuite/gcc.target/i386/pr126571-1.c
new file mode 100644
index 000000000000..7139a9a6f812
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr126571-1.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* PR tree-optimization/126571 */
+
+typedef __seg_fs  int *type1;
+
+int
+f (int c, type1 fp, int *q)
+{
+  int r;
+  if (c)
+    r = *fp;
+  else
+    r = *q;
+  return r + 1;
+}
diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index f6e407c0aad0..2ff26bfab73f 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -4287,6 +4287,9 @@ factor_out_conditional_load (edge e0, edge e1, basic_block merge, gphi *phi,
 	 FIXME: Refine to check ADDRESSABLE bit.  */
       if (TREE_CODE (p0) != SSA_NAME || TREE_CODE (p1) != SSA_NAME)
 	return false;
+      // Incompatible address spaces or differnt function pointers could show up here.
+      if (!types_compatible_p (TREE_TYPE (p0), TREE_TYPE (p1)))
+	return false;
       /* Build P' = PHI <P, Q> and the single load result = *P'.  */
       newptr = make_ssa_name (TREE_TYPE (p0));
       gphi *pphi = create_phi_node (newptr, merge);