[gcc r12-8227] fortran: Pre-evaluate string pointers. [PR102043]

[gcc r12-8227] fortran: Pre-evaluate string pointers. [PR102043]

[Mikael Morin]

https://gcc.gnu.org/g:89ca0fffa48b799b228beee48a16e26e24d8e199

commit r12-8227-g89ca0fffa48b799b228beee48a16e26e24d8e199
Author: Mikael Morin <mikael@gcc.gnu.org>
Date:   Fri Apr 22 22:52:12 2022 +0200

    fortran: Pre-evaluate string pointers. [PR102043]
    
    This avoids a regression on deferred_character_23.f90 later in the
    patch series when array references are rewritten to use pointer
    arithmetic.
    
    The problem is a SAVE_EXPR tree as TYPE_SIZE_UNIT of one array element
    type, which is used by the pointer arithmetic expressions.  As these
    expressions appear in both branches of an if-then-else block, the tree
    is lowered to a variable in one of the branches but it’s used in both
    branches, which is invalid middle-end code.
    
    This change pre-evaluates the array references or pointer arithmetics
    to variables before the if-then-else block, so that the SAVE_EXPR are
    expanded to variables in the parent scope of the if-then-else block,
    and expressions referencing the variables remain valid in both
    branches.
    
            PR fortran/102043
    
    gcc/fortran/ChangeLog:
            * trans-expr.cc: Pre-evaluate src and dest to variables
            before using them.
    
    gcc/testsuite/ChangeLog:
            * gfortran.dg/dependency_49.f90: Update variable occurence
            count.

Diff:
---
 gcc/fortran/trans-expr.cc                   | 7 +++++++
 gcc/testsuite/gfortran.dg/dependency_49.f90 | 3 ++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/gcc/fortran/trans-expr.cc b/gcc/fortran/trans-expr.cc
index ab710efc451..d7a368a685f 100644
--- a/gcc/fortran/trans-expr.cc
+++ b/gcc/fortran/trans-expr.cc
@@ -8093,6 +8093,13 @@ gfc_trans_string_copy (stmtblock_t * block, tree dlength, tree dest,
   cond2 = fold_build2_loc (input_location, LT_EXPR, logical_type_node, slen,
 			   dlen);
 
+  /* Pre-evaluate pointers unless one of the IF arms will be optimized away.  */
+  if (!CONSTANT_CLASS_P (cond2))
+    {
+      dest = gfc_evaluate_now (dest, block);
+      src = gfc_evaluate_now (src, block);
+    }
+
   /* Copy and pad with spaces.  */
   tmp3 = build_call_expr_loc (input_location,
 			      builtin_decl_explicit (BUILT_IN_MEMMOVE),
diff --git a/gcc/testsuite/gfortran.dg/dependency_49.f90 b/gcc/testsuite/gfortran.dg/dependency_49.f90
index 73d517e8f76..9638f65c069 100644
--- a/gcc/testsuite/gfortran.dg/dependency_49.f90
+++ b/gcc/testsuite/gfortran.dg/dependency_49.f90
@@ -11,4 +11,5 @@ program main
   a%x = a%x(2:3)
   print *,a%x
 end program main
-! { dg-final { scan-tree-dump-times "__var_1" 4 "original" } }
+! The temporary var appears three times: declaration, copy-in and copy-out
+! { dg-final { scan-tree-dump-times "__var_1" 3 "original" } }