[gcc r17-2006] Expand TMR fixup when we end up with a (void *)0 base

[Richard Biener]

https://gcc.gnu.org/g:952725ad810600bf6b0730e3a121dca2fbd2c6ce

commit r17-2006-g952725ad810600bf6b0730e3a121dca2fbd2c6ce
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Jun 29 13:08:07 2026 +0200

    Expand TMR fixup when we end up with a (void *)0 base
    
    When create_mem_ref falls back to a (void *)0 base address we
    currently only fall back to LEA plus indirection when the target
    can use a second index register.  But we also need to do this
    if there's a scaled by one index.  Or rather always to be safe.
    
            * tree-ssa-loop-ivopts.cc (rewrite_use_address): Always
            avoid TARGET_MEM_REF with a base of zero.
            * tree-ssa-sccvn.cc (vn_reference_maybe_forwprop_address): Do
            not forward TARGET_MEM_REF addresses.

Diff:
---
 gcc/tree-ssa-loop-ivopts.cc | 3 +--
 gcc/tree-ssa-sccvn.cc       | 3 +++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/gcc/tree-ssa-loop-ivopts.cc b/gcc/tree-ssa-loop-ivopts.cc
index 4ca553251887..f8dfc77de4ae 100644
--- a/gcc/tree-ssa-loop-ivopts.cc
+++ b/gcc/tree-ssa-loop-ivopts.cc
@@ -7639,11 +7639,10 @@ rewrite_use_address (struct ivopts_data *data,
   else
     {
       /* When we end up confused enough and have no suitable base but
-	 stuffed everything to index2 use a LEA for the address and
+	 stuffed everything to indexes use a LEA for the address and
 	 create a plain MEM_REF to avoid basing a memory reference
 	 on address zero which create_mem_ref_raw does as fallback.  */
       if (TREE_CODE (ref) == TARGET_MEM_REF
-	  && TMR_INDEX2 (ref) != NULL_TREE
 	  && integer_zerop (TREE_OPERAND (ref, 0)))
 	{
 	  ref = fold_build1 (ADDR_EXPR, TREE_TYPE (TREE_OPERAND (ref, 0)), ref);
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index 98b837be01d0..a95350abccbf 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -1507,6 +1507,9 @@ vn_reference_maybe_forwprop_address (vec<vn_reference_op_s> *ops,
 		      = wide_int_to_tree (TREE_TYPE (mem_op->op0),
 					  wi::to_poly_wide (new_mem_op->op0));
 		}
+	      /* Do not forward addresses of TARGET_MEM_REF.  */
+	      else if (tem[0].opcode == TARGET_MEM_REF)
+		return changed;
 	      else
 		gcc_assert (tem.last ().opcode == STRING_CST);
 	      ops->pop ();