[PATCH] middle-end/106331 - fix mem attributes for string op arguments

[Richard Biener <rguenther@suse.de>]

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.

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

	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.
---
 gcc/builtins.cc                        | 13 +++++++++----
 gcc/testsuite/gfortran.dg/pr106331.f90 |  7 +++++++
 2 files changed, 16 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/gfortran.dg/pr106331.f90

diff --git a/gcc/builtins.cc b/gcc/builtins.cc
index 35b9197945f..bc05a40bfe7 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
-- 
2.35.3