On 7/11/25 9:09 AM, Jakub Jelinek wrote:
On Thu, Jul 10, 2025 at 04:35:49PM -0400, Jason Merrill wrote:
@@ -211,8 +211,27 @@ mark_use (tree expr, bool rvalue_p, bool
}
return expr;
}
- gcc_fallthrough();
+ gcc_fallthrough ();
CASE_CONVERT:
+ if (VOID_TYPE_P (TREE_TYPE (expr)))
+ switch (TREE_CODE (TREE_OPERAND (expr, 0)))
+ {
+ case PREINCREMENT_EXPR:
+ case PREDECREMENT_EXPR:
+ case POSTINCREMENT_EXPR:
+ case POSTDECREMENT_EXPR:
Why is this specific to these codes? I would think we would want consistent
handling of (void) here and in mark_exp_read.
The second/third levels of the warnings (i.e. the new ones) want
++op0
--op0
op0++
op0--
not to be treated as uses of op0 (but op1 = ++op0 etc. counts as use).
Which is why it checks for these special cases. The cast to void is there
to just ignore the pre/post inc/decrements alone when their value isn't
used.
The above mark_exp_read changes wouldn't be needed if
case PREINCREMENT_EXPR:
case PREDECREMENT_EXPR:
case POSTINCREMENT_EXPR:
case POSTDECREMENT_EXPR:
mark_exp_read (TREE_OPERAND (exp, 0));
break;
weren't added, but that is needed so that x = ++op0; etc. are treated as
use of op0, while ++op0; on its own is not.
Coming back to this comment, it still seems to me that we can generalize
this and ignore anything cast to void here, as in the below; after
something has been cast to void, it can no longer be read. I don't get
any regressions from this simplification, either.
We might generalize to anything of void type, but I haven't tested that.
commit adcf4220b73a9b7f44a35728f60aa5b351ef51d8
Author: Jason Merrill <ja...@redhat.com>
Date: Mon Jul 14 18:29:17 2025 -0400
void
diff --git a/gcc/cp/expr.cc b/gcc/cp/expr.cc
index 8b5a098ecb3..e4a7cfd7bec 100644
--- a/gcc/cp/expr.cc
+++ b/gcc/cp/expr.cc
@@ -214,24 +214,7 @@ mark_use (tree expr, bool rvalue_p, bool read_p,
gcc_fallthrough ();
CASE_CONVERT:
if (VOID_TYPE_P (TREE_TYPE (expr)))
- switch (TREE_CODE (TREE_OPERAND (expr, 0)))
- {
- case PREINCREMENT_EXPR:
- case PREDECREMENT_EXPR:
- case POSTINCREMENT_EXPR:
- case POSTDECREMENT_EXPR:
- tree op0;
- op0 = TREE_OPERAND (TREE_OPERAND (expr, 0), 0);
- STRIP_ANY_LOCATION_WRAPPER (op0);
- if ((VAR_P (op0) || TREE_CODE (op0) == PARM_DECL)
- && !DECL_READ_P (op0)
- && (VAR_P (op0) ? warn_unused_but_set_variable
- : warn_unused_but_set_parameter) > 1)
- read_p = false;
- break;
- default:
- break;
- }
+ read_p = false;
recurse_op[0] = true;
break;
@@ -382,16 +365,7 @@ mark_exp_read (tree exp)
break;
CASE_CONVERT:
if (VOID_TYPE_P (TREE_TYPE (exp)))
- switch (TREE_CODE (TREE_OPERAND (exp, 0)))
- {
- case PREINCREMENT_EXPR:
- case PREDECREMENT_EXPR:
- case POSTINCREMENT_EXPR:
- case POSTDECREMENT_EXPR:
- return;
- default:
- break;
- }
+ return;
/* FALLTHRU */
case ARRAY_REF:
case COMPONENT_REF:
