[gcc r16-7999] fold-mem-offsets: Fix wrong mode in memory_address_addr_space_p

[Philipp Tomsich]

https://gcc.gnu.org/g:c37b65b3348dbca9f99040f95937f12c75e2446e

commit r16-7999-gc37b65b3348dbca9f99040f95937f12c75e2446e
Author: Philipp Tomsich <philipp.tomsich@vrull.eu>
Date:   Mon Feb 23 17:22:47 2026 +0100

    fold-mem-offsets: Fix wrong mode in memory_address_addr_space_p
    
    The validity check in do_check_validity was passing the address mode
    (GET_MODE of the address RTX, e.g. DImode) to memory_address_addr_space_p
    instead of the memory access mode (GET_MODE of the MEM RTX, e.g. SImode).
    The first argument to memory_address_addr_space_p is the mode of the
    memory access, not the address mode.
    
    On targets where address validity depends on the access width (e.g.
    alignment-sensitive modes, vector modes), this could accept an illegal
    offset or reject a valid one.
    
    Rename the variable to 'addr_mode' for address construction and add a
    separate 'mem_mode' for the validity check.
    
    gcc/ChangeLog:
    
            * fold-mem-offsets.cc (do_check_validity): fix wrong mode
            and rename arguments to avoid future confusion

Diff:
---
 gcc/fold-mem-offsets.cc | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/gcc/fold-mem-offsets.cc b/gcc/fold-mem-offsets.cc
index 9ac4a59ace6b..1cd2dc036c2f 100644
--- a/gcc/fold-mem-offsets.cc
+++ b/gcc/fold-mem-offsets.cc
@@ -688,14 +688,16 @@ do_check_validity (rtx_insn *insn, fold_mem_info *info)
   int icode = INSN_CODE (insn);
   INSN_CODE (insn) = -1;
   rtx mem_addr = XEXP (mem, 0);
-  machine_mode mode = GET_MODE (mem_addr);
+  machine_mode addr_mode = GET_MODE (mem_addr);
+  machine_mode mem_mode = GET_MODE (mem);
   if (new_offset != 0)
-    XEXP (mem, 0) = gen_rtx_PLUS (mode, reg, gen_int_mode (new_offset, mode));
+    XEXP (mem, 0) = gen_rtx_PLUS (addr_mode, reg,
+				   gen_int_mode (new_offset, addr_mode));
   else
     XEXP (mem, 0) = reg;
 
   bool illegal = insn_invalid_p (insn, false)
-		 || !memory_address_addr_space_p (mode, XEXP (mem, 0),
+		 || !memory_address_addr_space_p (mem_mode, XEXP (mem, 0),
 						  MEM_ADDR_SPACE (mem));
 
   /* Restore the instruction.  */