gimplify: Don't optimize register const vars to static [PR93949]

The following testcase is rejected, while it was accepted in 3.4 and earlier
(before tree-ssa merge).
The problem is that we decide to promote the const variable to TREE_STATIC,
but TREE_STATIC DECL_REGISTER VAR_DECLs may only be the global register vars
and so assemble_variable/make_decl_rtl diagnoses it.

Either we do what the following patch does, where we could consider
register as a hint the user doesn't want such optimization, because if
something is forced static, it is not "register" anymore and register static
is not valid in C either, or we could clear DECL_REGISTER instead, but would
still need to punt at least on DECL_HARD_REGISTER cases.

2020-02-27  Jakub Jelinek  <jakub@redhat.com>

	PR c/93949
	* gimplify.c (gimplify_init_constructor): Don't promote readonly
	DECL_REGISTER variables to TREE_STATIC.

	* gcc.c-torture/compile/pr93949.c: New test.

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 38bfbb9..d8cfd09 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,9 @@
 2020-02-27  Jakub Jelinek  <jakub@redhat.com>
 
+       PR c/93949
+       * gimplify.c (gimplify_init_constructor): Don't promote readonly
+       DECL_REGISTER variables to TREE_STATIC.
+
        PR tree-optimization/93582
        PR tree-optimization/93945
        * tree-ssa-sccvn.c (vn_reference_lookup_3): Handle memset with

diff --git a/gcc/gimplify.c b/gcc/gimplify.c
index a6205d6..ef531f3 100644 (file)
--- a/gcc/gimplify.c
+++ b/gcc/gimplify.c
@@ -4923,6 +4923,7 @@ gimplify_init_constructor (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p,
            && num_nonzero_elements > 1
            && TREE_READONLY (object)
            && VAR_P (object)
+           && !DECL_REGISTER (object)
            && (flag_merge_constants >= 2 || !TREE_ADDRESSABLE (object))
            /* For ctors that have many repeated nonzero elements
               represented through RANGE_EXPRs, prefer initializing

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 70897c5..3cc13f9 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 2020-02-27  Jakub Jelinek  <jakub@redhat.com>
 
+       PR c/93949
+       * gcc.c-torture/compile/pr93949.c: New test.
+
        PR tree-optimization/93582
        PR tree-optimization/93945
        * gcc.dg/tree-ssa/pr93582-9.c: New test.

diff --git a/gcc/testsuite/gcc.c-torture/compile/pr93949.c b/gcc/testsuite/gcc.c-torture/compile/pr93949.c
new file mode 100644 (file)
index 0000000..bbda020
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr93949.c
@@ -0,0 +1,7 @@
+/* PR c/93949 */
+
+void
+foo (void)
+{
+  register const double d[3] = { 0., 1., 2. };
+}