[gcc r13-1990] Fix middle-end/103645: empty struct store not removed when using compound literal

[Andrew Pinski <pinskia@gcc.gnu.org>]

https://gcc.gnu.org/g:21c7aab09805d0c8c7695c8a69c8715d673a739a

commit r13-1990-g21c7aab09805d0c8c7695c8a69c8715d673a739a
Author: Andrew Pinski <apinski@marvell.com>
Date:   Mon Dec 20 20:27:33 2021 -0800

    Fix middle-end/103645: empty struct store not removed when using compound literal
    
    For compound literals empty struct stores are not removed as they go down a
    different path of the gimplifier; trying to optimize the init constructor.
    This fixes the problem by not adding the gimple assignment at the end
    of gimplify_init_constructor if it was an empty type.
    
    Note this updates gcc.dg/pr87052.c where we had:
    const char d[0] = { };
    And was expecting a store to d but after this, there is no store
    as the decl's type is zero in size.
    
    OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.
    
    gcc/ChangeLog:
    
            PR middle-end/103645
            * gimplify.cc (gimplify_init_constructor): Don't build/add
            gimple assignment of an empty type.
    
    gcc/testsuite/ChangeLog:
            * gcc.dg/pr87052.c: Update d var to expect nothing.

Diff:
---
 gcc/gimplify.cc                | 7 +++++--
 gcc/testsuite/gcc.dg/pr87052.c | 6 +++---
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
index 2ac7ca0855e..f0fbdb48012 100644
--- a/gcc/gimplify.cc
+++ b/gcc/gimplify.cc
@@ -5488,8 +5488,11 @@ gimplify_init_constructor (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p,
   if (ret == GS_ERROR)
     return GS_ERROR;
   /* If we have gimplified both sides of the initializer but have
-     not emitted an assignment, do so now.  */
-  if (*expr_p)
+     not emitted an assignment, do so now.   */
+  if (*expr_p
+      /* If the type is an empty type, we don't need to emit the
+	 assignment. */
+      && !is_empty_type (TREE_TYPE (TREE_OPERAND (*expr_p, 0))))
     {
       tree lhs = TREE_OPERAND (*expr_p, 0);
       tree rhs = TREE_OPERAND (*expr_p, 1);
diff --git a/gcc/testsuite/gcc.dg/pr87052.c b/gcc/testsuite/gcc.dg/pr87052.c
index 18e092c4674..796fe6440c1 100644
--- a/gcc/testsuite/gcc.dg/pr87052.c
+++ b/gcc/testsuite/gcc.dg/pr87052.c
@@ -23,8 +23,7 @@ void test (void)
 
   const char d[0] = { };
 
-  /* Expect the following:
-     d = ""; */
+  /* Expect nothing.  */
 
   const char e[0] = "";
 
@@ -36,6 +35,7 @@ void test (void)
 /* { dg-final { scan-tree-dump-times "a = \"\\\\x00ab\";" 1 "gimple" } }
    { dg-final { scan-tree-dump-times "b = \"a\\\\x00bc\";"  1 "gimple" } }
    { dg-final { scan-tree-dump-times "c = \"\";"  1 "gimple" } }
-   { dg-final { scan-tree-dump-times "d = { *};"  1 "gimple" } }
+   { dg-final { scan-tree-dump-times "d = "  1 "gimple" } }
+   { dg-final { scan-tree-dump-times "d = {CLOBBER\\(eol\\)}"  1 "gimple" } }
    { dg-final { scan-tree-dump-times "e = "  1 "gimple" } }
    { dg-final { scan-tree-dump-times "e = {CLOBBER\\(eol\\)}"  1 "gimple" } }  */