On 6/9/25 4:12 PM, Iain Sandoe wrote:
Hi Jason,
There was some discussion of this in the PR116775 comments. In the
end I have matched what clang does in this circumstance, since that
seems reasonable - and we may ignore the attributes as needed.
tested on x86-64-darwin, powerpc64le-linux, OK for trunk?
thanks
Iain
--- 8< ---
Here we have an expression that is not evaluated but is still seen
as potentially-evaluated. We handle this by determining if the
operand has side-effects, producing a warning that the assume has
been ignored and eliding it.
gcc/cp/ChangeLog:
* coroutines.cc (analyze_expression_awaits): Elide assume
attributes containing await expressions, since these have
side effects. Emit a diagnostic that this has been done.
gcc/testsuite/ChangeLog:
* g++.dg/coroutines/assume.C: New test.
---
gcc/cp/coroutines.cc | 13 ++++++++
gcc/testsuite/g++.dg/coroutines/assume.C | 40 ++++++++++++++++++++++++
2 files changed, 53 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/coroutines/assume.C
diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index bbdc33abc0e..21b1d85b02c 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -3587,6 +3587,19 @@ analyze_expression_awaits (tree *stmt, int *do_subtree,
void *d)
}
*do_subtree = 0;
}
+ else if (!fn && CALL_EXPR_IFN (*stmt) == IFN_ASSUME)
+ {
+ tree expr = CALL_EXPR_ARG (*stmt, 0);
+ if (TREE_SIDE_EFFECTS (expr))
+ {
+ location_t loc_e = cp_expr_location (expr);
+ location_t loc_s = cp_expr_location (*stmt);
+ location_t loc_n = make_location (loc_e, loc_s, loc_s);
+ warning_at (loc_n, OPT_Wattributes,"assumption ignored"
+ " because it contains possible side-effects");
+ *stmt = build_empty_stmt (loc_n);
+ }
+ }
Why is this in coroutines.cc?
We do badly at assume of even trivial calls
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118995) but any warning
about that should be emitted by the code that chooses to give up, not in
the front end.
Jason
