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ipa/100373 - fix emutls lowering compare-debug issue

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emutls figured that tls uses in debug-insns need lowering but
that obviously has effects on code-generation as can be seen
in the following IL diff with the new testcase:

   <bb 2> [local count: 1073741824]:
-  a = 0;
+  # DEBUG BEGIN_STMT
   _4 = __builtin___emutls_get_address (&__emutls_v.b);
+  # DEBUG D#1 => *_4
+  # DEBUG d => (long int) D#1
+  # DEBUG BEGIN_STMT
+  a = 0;
+  # DEBUG BEGIN_STMT
   *_4 = 0;
   return;

where it figured the debug use of b in the original

  <bb 2> [local count: 1073741824]:
  # DEBUG BEGIN_STMT
  # DEBUG D#1 => b
  # DEBUG d => (long int) D#1
  # DEBUG BEGIN_STMT
  a = 0;

needs lowering (it maybe does when we want to produce perfect
debug but that's just bad luck).

The following patch fixes this by avoiding to create a new
emutls address when visiting debug stmts and instead resets them.
Another option might be to simply not lower debug stmt uses
but I have no way to verify actual debug info for this.

2021-05-05  Richard Biener  <rguenther@suse.de>

	PR ipa/100373
	* tree-emutls.c (gen_emutls_addr): Pass in whether we're
	dealing with a debug use and only query existing addresses
	if so.
	(lower_emutls_1): Avoid splitting out addresses for debug
	stmts, reset the debug stmt when we fail to find existing
	lowered addresses.
	(lower_emutls_phi_arg): Set wi.stmt.

	* gcc.dg/pr100373.c: New testcase.
This commit is contained in:
Richard Biener 2021-05-05 10:15:27 +02:00
parent 2fd7689cb2
commit b5254d6b75
2 changed files with 24 additions and 4 deletions
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11
gcc/testsuite/gcc.dg/pr100373.c Normal file
View File

@ -0,0 +1,11 @@
/* { dg-do compile } */
/* { dg-options "-O2 -fcompare-debug" } */
int a;
_Thread_local int b;
void c()
{
long d = b;
a = 0;
b = 0;
}

17
gcc/tree-emutls.c
View File

@ -394,13 +394,13 @@ struct lower_emutls_data
Append any new computation statements required to D->SEQ. */
static tree
gen_emutls_addr (tree decl, struct lower_emutls_data *d)
gen_emutls_addr (tree decl, struct lower_emutls_data *d, bool for_debug)
{
/* Compute the address of the TLS variable with help from runtime. */
tls_var_data *data = tls_map->get (varpool_node::get (decl));
tree addr = data->access;
if (addr == NULL)
if (addr == NULL && !for_debug)
{
varpool_node *cvar;
tree cdecl;
@ -480,7 +480,7 @@ lower_emutls_1 (tree *ptr, int *walk_subtrees, void *cb_data)
*ptr = t = unshare_expr (t);
/* If we're allowed more than just is_gimple_val, continue. */
if (!wi->val_only)
if (!wi->val_only || is_gimple_debug (wi->stmt))
{
*walk_subtrees = 1;
return NULL_TREE;
@ -536,7 +536,15 @@ lower_emutls_1 (tree *ptr, int *walk_subtrees, void *cb_data)
return NULL_TREE;
}
addr = gen_emutls_addr (t, d);
addr = gen_emutls_addr (t, d, is_gimple_debug (wi->stmt));
if (!addr)
{
gimple_debug_bind_reset_value (wi->stmt);
update_stmt (wi->stmt);
wi->changed = false;
/* Stop walking operands. */
return error_mark_node;
}
if (is_addr)
{
/* Replace "&var" with "addr" in the statement. */
@ -590,6 +598,7 @@ lower_emutls_phi_arg (gphi *phi, unsigned int i,
memset (&wi, 0, sizeof (wi));
wi.info = d;
wi.val_only = true;
wi.stmt = phi;
walk_tree (&pd->def, lower_emutls_1, &wi, NULL);
/* For normal statements, we let update_stmt do its job. But for phi