Hi!
The following invalid testcase ICEs, because we:
1) for some strange reason ignore invalid punctuations in
parse_output_constraint, which has just
default:
if (!ISALPHA (*p))
break;
compared to parse_input_constraint
default:
if (! ISALPHA (constraint[j]))
{
error ("invalid punctuation %qc in constraint", constraint[j]);
return false;
}
Haven't touched this because I fear it could break real-world code
2) the checking whether = or + is first in the output constraint is
a warning only:
if (p != constraint)
warning (0, "output constraint %qc for operand %d "
"is not at the beginning",
*p, operand_num);
3) parse_input_constraint parses also the corresponding output constraint
if the input constraint has a number as the only variant, but
even the comment removed in the following patch explains that it
doesn't work correctly and skips the first character; now, usually
that is not a big deal because if the first character of the output
constraint is = or + as it should, then the checking doesn't do anything;
but as 2) is just a warning, we accept it and then we fail to check it
4) far later on we parse the whole output constraint when input constraint
refers to it and assert it succeeds, which it doesn't due to 1), 2) and 3)
The following patch fixes the 3) spot, when switching to the output
constraint, instead of setting j = 0; and break; (== continue;) so that it
first does j += CONSTRAINT_LEN (constraint[0], constraint+0) and thus
usually starts at second, sometimes third character of the output constraint
it uses goto before the loop which sets j = 0; and doesn't do the j += ...
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2026-01-08 Jakub Jelinek <[email protected]>
PR middle-end/111817
* stmt.cc (parse_input_constraint): For matching construct, goto
before the loop without changing j instead of break. Remove comment
about that problem.
* c-c++-common/pr111817.c: New test.
--- gcc/stmt.cc.jj 2026-01-02 09:56:10.331333745 +0100
+++ gcc/stmt.cc 2026-01-07 15:57:35.329401594 +0100
@@ -508,6 +508,7 @@ parse_input_constraint (const char **con
unsigned int alt = 0;
unsigned long match = 0;
+repeat:
for (j = 0; j < c_len; j += CONSTRAINT_LEN (constraint[j], constraint+j))
switch (constraint[j])
{
@@ -583,12 +584,7 @@ parse_input_constraint (const char **con
constraint = constraints[match];
*constraint_p = constraint;
c_len = strlen (constraint);
- j = 0;
- /* ??? At the end of the loop, we will skip the first part of
- the matched constraint. This assumes not only that the
- other constraint is an output constraint, but also that
- the '=' or '+' come first. */
- break;
+ goto repeat;
}
else
j = end - constraint;
--- gcc/testsuite/c-c++-common/pr111817.c.jj 2026-01-07 17:07:23.449815574
+0100
+++ gcc/testsuite/c-c++-common/pr111817.c 2026-01-07 17:10:47.408343658
+0100
@@ -0,0 +1,9 @@
+/* PR middle-end/111817 */
+/* { dg-do compile } */
+
+int
+foo (int x, int y)
+{
+ asm ("" : "\n=g" (x) : "0" (y)); /* { dg-warning "output constraint '='
for operand 0 is not at the beginning" } */
+ return x; /* { dg-error "invalid punctuation
'\\\\x\[0-9a-zA-Z]*' in constraint" "" { target *-*-* } .-1 } */
+}
Jakub
