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.

diff --git a/gcc/builtins.cc b/gcc/builtins.cc
index 91b9c9f0875a12fb0a94db9a47ce3b4a45db5f39..0d13197703d9388e87a64b9620663f3e26881dfc 100644 (file)
--- 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 (file)
index 0000000..3873863
--- /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