[gcc r12-8584] middle-end/106331 - fix mem attributes for string op arguments

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:1a7200da71550e6f92da66f0b328bb20d3bcdf35

commit r12-8584-g1a7200da71550e6f92da66f0b328bb20d3bcdf35
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Jul 19 09:57:22 2022 +0200

    middle-end/106331 - fix mem attributes for string op arguments
    
    get_memory_rtx tries hard to come up with a MEM_EXPR to record
    in the memory attributes but in the last fallback fails to properly
    account for an unknown offset and thus, as visible in this testcase,
    incorrect alignment computed from set_mem_attributes.  The following
    rectifies both parts.
    
            PR middle-end/106331
            * builtins.cc (get_memory_rtx): Compute alignment from
            the original address and set MEM_OFFSET to unknown when
            we create a MEM_EXPR from the base object of the address.
    
            * gfortran.dg/pr106331.f90: New testcase.
    
    (cherry picked from commit e4ff11a8f2e80adb8ada69bf35ee6a1ab18a9c85)

Diff:
---
 gcc/builtins.cc                        | 13 +++++++++----
 gcc/testsuite/gfortran.dg/pr106331.f90 |  7 +++++++
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/gcc/builtins.cc b/gcc/builtins.cc
index 85459200a09..57929a42bc4 100644
--- a/gcc/builtins.cc
+++ b/gcc/builtins.cc
@@ -1360,7 +1360,7 @@ expand_builtin_prefetch (tree exp)
 rtx
 get_memory_rtx (tree exp, tree len)
 {
-  tree orig_exp = exp;
+  tree orig_exp = exp, base;
   rtx addr, mem;
 
   /* When EXP is not resolved SAVE_EXPR, MEM_ATTRS can be still derived
@@ -1391,10 +1391,11 @@ get_memory_rtx (tree exp, tree len)
   if (is_gimple_mem_ref_addr (TREE_OPERAND (exp, 0)))
     set_mem_attributes (mem, exp, 0);
   else if (TREE_CODE (TREE_OPERAND (exp, 0)) == ADDR_EXPR
-	   && (exp = get_base_address (TREE_OPERAND (TREE_OPERAND (exp, 0),
-						     0))))
+	   && (base = get_base_address (TREE_OPERAND (TREE_OPERAND (exp, 0),
+						      0))))
     {
-      exp = build_fold_addr_expr (exp);
+      unsigned int align = get_pointer_alignment (TREE_OPERAND (exp, 0));
+      exp = build_fold_addr_expr (base);
       exp = fold_build2 (MEM_REF,
 			 build_array_type (char_type_node,
 					   build_range_type (sizetype,
@@ -1402,6 +1403,10 @@ get_memory_rtx (tree exp, tree len)
 							     NULL)),
 			 exp, build_int_cst (ptr_type_node, 0));
       set_mem_attributes (mem, exp, 0);
+      /* Since we stripped parts make sure the offset is unknown and the
+	 alignment is computed from the original address.  */
+      clear_mem_offset (mem);
+      set_mem_align (mem, align);
     }
   set_mem_alias_set (mem, 0);
   return mem;
diff --git a/gcc/testsuite/gfortran.dg/pr106331.f90 b/gcc/testsuite/gfortran.dg/pr106331.f90
new file mode 100644
index 00000000000..3873863be48
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr106331.f90
@@ -0,0 +1,7 @@
+! { dg-do run }
+! { dg-options "-Og" }
+
+PROGRAM main
+  CHARACTER(LEN=24) :: a(2)
+  a = ''
+END PROGRAM