On 10/9/25 15:00, Sam James wrote:
Sandra Loosemore <[email protected]> writes:
On 10/8/25 21:15, Sam James wrote:
CCP interacts poorly with -Wmaybe-uninitialized in some cases by assuming a
value
which stops us warning about it (false negatives). Inform users about this
infamous interaction.
gcc/ChangeLog:
PR tree-optimization/18501
* doc/invoke.texi (-Wmaybe-uninitialized): Mention interaction
with
CCP.
---
That works for me. I've checked this in.
gcc/doc/invoke.texi | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index f93fe43733dc..8802d416b30c 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -8375,7 +8375,10 @@ known to read the object.) Annotating the function with
attribute
the object and avoids the warning (@pxref{Common Function Attributes}).
These warnings are only possible in optimizing compilation,
because otherwise
-GCC does not keep track of the state of variables.
+GCC does not keep track of the state of variables. On the other hand,
+@option{-Wmaybe-uninitialized} is known not to warn in many situations
+(false negatives) due to optimizations taking advantage of undefinedness
+of uninitialized uses like constant propagation.
These warnings are made optional because GCC may not be able to
determine when
the code is correct in spite of appearing to have an error. Here is one
I'm sorry, I can't parse this one. Do you maybe mean "optimizations
like constant propagation" instead of "uninitialized uses like
constant propagation"?
Read it as: "optimizations like constant propagation taking advantage of
uninitialized uses [of variables]". I'll change it to that if you're
fine with that phrasing?
Well, I'm confused. If we're not going to tell users what optimizations
to disable or what other options to use to get the best results, what's
the purpose of the added text? I guess I know more about typical
compiler optimization strategies and GCC's in particular than most users
and since I don't see an immediate connection between the warning and
constant propagation, I suspect this would be even more meaningless to
average users. We might as well just tell them that some optimizations
interfere with -Wmaybe-uninitialized, and leave it at that.
-Sandra
