Re: [fpc-devel] Unreachable code warnings
Daniël Mantione wrote:
Op Mon, 15 Oct 2007, schreef Michael Schnell:
So I guess the warning stays. We can discuss some extensions which makes
it easier to code such restrictions like merging parts of the tue branch.
Could the warning not simply be switched off and on (or set to some kind of
level) by a {$... line ?
It is on the to-do list already. However, I don't think it'll be the end
of the discussions; there will always be tension between the compiler
being helpfull to signal dubious code, and the compiler generating too
much noise.
The compiler will be used in different ways by different people for different needs. Thus,
viewpoints will differ ands that means that discussions about the pros and contras of a specific
warning can be endless. The way out, I believe, is an infrastructure where individual warnings can
be put on and off, like gpc and gcc have, e.g. see
http://gcc.gnu.org/onlinedocs/gcc-4.2.2/gcc/Warning-Options.html. I believe I heard that it is on
the todo list ?
Regards,
Adriaan van Os
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Re: [fpc-devel] Unreachable code warnings
Op Thu, 18 Oct 2007, schreef Adriaan van Os:
Daniël Mantione wrote:
Op Mon, 15 Oct 2007, schreef Michael Schnell:
So I guess the warning stays. We can discuss some extensions
which makes
it easier to code such restrictions like merging parts of the tue
branch.
Could the warning not simply be switched off and on (or set to some
kind of
level) by a {$... line ?
It is on the to-do list already. However, I don't think it'll be the end
of the discussions; there will always be tension between the compiler
being helpfull to signal dubious code, and the compiler generating too
much noise.
The compiler will be used in different ways by different people for different
needs. Thus, viewpoints will differ ands that means that discussions about the
pros and contras of a specific warning can be endless. The way out, I believe,
is an infrastructure where individual warnings can be put on and off, like gpc
and gcc have, e.g. see
http://gcc.gnu.org/onlinedocs/gcc-4.2.2/gcc/Warning-Options.html. I believe
I heard that it is on the todo list ?
Indeed it is.
Daniël___
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Re: [fpc-devel] Unreachable code warnings
Could the warning not simply be switched off and on (or set to some kind of
level) by a {$... line ?
It is on the to-do list already. However, I don't think it'll be the end
of the discussions; there will always be tension between the compiler
being helpfull to signal dubious code, and the compiler generating too
much noise.
The OP wanted to avoid a warning at a defined place in his code, because
he is sure that the code he wrote __in these lines__ is correct. So
being able to switch warnings on and off in the code would be easy to do
and very helpful.
-Michael
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Re: [fpc-devel] Unreachable code warnings
Maybe it would better be a hint. Seems reasonable to me. The unused parameter hint is likewise also unavoidable with function callback implementations sometimes. There is a good reason for that the unreachable code is a warning: The compiler _changes_ your code by removing the if-branch. When it is a hint the compiler only has recognized a pattern, but it does not modify anything. Peter ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
Peter Vreman wrote: There is a good reason for that the unreachable code is a warning: The compiler _changes_ your code by removing the if-branch. When it is a hint the compiler only has recognized a pattern, but it does not modify anything. It changes it, but semantically it's the same right? In your reasoning, the compiler should also emit a warning when it does (or would do) common subexpression extraction. Micha ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
Micha Nelissen schrieb:
Peter Vreman wrote:
There is a good reason for that the unreachable code is a warning: The
compiler _changes_ your
code by removing the if-branch. When it is a hint the compiler only
has recognized a pattern, but
it does not modify anything.
It changes it, but semantically it's the same right?
In your reasoning, the compiler should also emit a warning when it does
There were enough other reasons.
(or would do) common subexpression extraction.
Anyways, gcc warns similiar, even two times ;):
~ cat test.c
int f(unsigned char c)
{
if (c0 || c255)
return 1;
return 0;
}
~ gcc -c test.c
test.c: In function ‘f’:
test.c:3: warning: comparison is always false due to limited range of
data type
test.c:3: warning: comparison is always false due to limited range of
data type
So I guess the warning stays. We can discuss some extensions which makes
it easier to code such restrictions like merging parts of the tue branch.
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Re: [fpc-devel] Unreachable code warnings
Florian Klaempfl wrote: ~ gcc -c test.c test.c: In function ‘f’: test.c:3: warning: comparison is always false due to limited range of data type test.c:3: warning: comparison is always false due to limited range of data type Yes, very annoying in gcc as well. It also warns when a variable is shadowed, a similar annoying warning. GCC doesn't even have hints AFAIK. Micha ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
So I guess the warning stays. We can discuss some extensions which makes
it easier to code such restrictions like merging parts of the tue branch.
Could the warning not simply be switched off and on (or set to some kind
of level) by a {$... line ?
-Michael
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Re: [fpc-devel] Unreachable code warnings
Op Mon, 15 Oct 2007, schreef Michael Schnell:
So I guess the warning stays. We can discuss some extensions which makes
it easier to code such restrictions like merging parts of the tue branch.
Could the warning not simply be switched off and on (or set to some kind of
level) by a {$... line ?
It is on the to-do list already. However, I don't think it'll be the end
of the discussions; there will always be tension between the compiler
being helpfull to signal dubious code, and the compiler generating too
much noise.
Daniël___
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[fpc-devel] Unreachable code warnings
Hi, I want to bring up the warning of unreachable code. If one is implementing code according to some spec, e.g. RFC, or what else, it occurs that that requires a sanity check on user input. If it now happens that the type of variable by accident guarantees that this is true; this is fine, the compiler might optimize the check away. The compiler should not give a warning though IMHO, because the check is necessary according to spec, and it might become necessary if someone decides to change the type of the variable being checked to have a wider range. Furthermore, the warning is not suppressible. Micha ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
Op Sun, 14 Oct 2007, schreef Micha Nelissen:
Hi,
I want to bring up the warning of unreachable code. If one is
implementing code according to some spec, e.g. RFC, or what else, it
occurs that that requires a sanity check on user input. If it now
happens that the type of variable by accident guarantees that this is
true; this is fine, the compiler might optimize the check away. The
compiler should not give a warning though IMHO, because the check is
necessary according to spec, and it might become necessary if someone
decides to change the type of the variable being checked to have a wider
range. Furthermore, the warning is not suppressible.
You mean this:
var b:byte;
f:file;
begin
{...}
blockread(f,b,sizeof(b))l
if (b0) or (b255) then
begin
writeln('Error: Invalid value');
halt(255);
end;
{...}
end;
IMO the compiler in the case above totally correct to let you know the
error condition can never occur. Even if a specification says 255 is the
maximum, the code is totally bogus.
It is justified to warn, since in some cases an error situation can occur
but the way the check is written causes a dead code check. We found a few
of these in the compiler sources.
Daniël___
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Re: [fpc-devel] Unreachable code warnings
Daniël Mantione wrote: A warning should always be fixable and doing so, turning it into correct code. The compiler is simply wrong here; my code is correct, so it should not complain. The warning is fixable: Remove the superfluous check. Sigh. That's my point. If you were using smallint before, and someone changes the type to integer, then a bug is introduced; so you don't want to remove the check but the compiler can of course optimize it away. Micha ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
Op Sun, 14 Oct 2007, schreef Micha Nelissen: Daniël Mantione wrote: A warning should always be fixable and doing so, turning it into correct code. The compiler is simply wrong here; my code is correct, so it should not complain. The warning is fixable: Remove the superfluous check. Sigh. That's my point. If you were using smallint before, and someone changes the type to integer, then a bug is introduced; so you don't want to remove the check but the compiler can of course optimize it away. A solution is to make a dedicated type, and write down comments near its declaration. If you remove the warning, code like: if ahigh(a) then ... no longer warns, which results in dead code in many situations. I can follow your reasoning why you want the dead code, but on the other hand the warning is there with good reason. Daniël___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
On 14 Oct 2007, at 22:06, Daniël Mantione wrote: I can follow your reasoning why you want the dead code, but on the other hand the warning is there with good reason. Maybe it would better be a hint. Jonas___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
Jonas Maebe schrieb: On 14 Oct 2007, at 22:06, Daniël Mantione wrote: I can follow your reasoning why you want the dead code, but on the other hand the warning is there with good reason. Maybe it would better be a hint. With the same reasoning you could make every warning a hint. Instead of if one usually uses asserts to check certain conditions. ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
On 14 Oct 2007, at 22:25, Florian Klaempfl wrote: Jonas Maebe schrieb: On 14 Oct 2007, at 22:06, Daniël Mantione wrote: I can follow your reasoning why you want the dead code, but on the other hand the warning is there with good reason. Maybe it would better be a hint. With the same reasoning you could make every warning a hint. I don't think so. While there may be false uninitialised warnings (because the compiler simply missed the initialisation somehow), every use of an uninitialised variable is an error. However, not every case of an if-expression which can evaluated at compile time is an error. I even don't think the majority is. Instead of if one usually uses asserts to check certain conditions. These constructions can also be used instead of ifdefs, even though ifdefs are probably also more often used. Using if's instead is however not wrong imho. Jonas ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
Florian Klaempfl wrote: Maybe it would better be a hint. With the same reasoning you could make every warning a hint. Instead of if one usually uses asserts to check certain conditions. Most are about bad code, that can be made better, AFAIK. E.g. 'an inherited method is hidden' needs a 'override;' or 'reintroduce;'. Micha ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
Jonas Maebe wrote: Maybe it would better be a hint. Seems reasonable to me. The unused parameter hint is likewise also unavoidable with function callback implementations sometimes. Micha ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
Joao Morais schrieb:
Daniël Mantione wrote:
The warning is fixable: Remove the superfluous check.
All,
a new contribution to this theme. What about this warning:
{$mode objfpc}
uses sysutils;
function testresult: boolean;
begin
raise exception.create('foo');
end;
begin
testresult;
end.
The compiler warns that the result wasn't assigned, but that function's
result simply cannot be reached.
Fixed in trunk when compiled with -Oodfa which will be probably a
default in 2.4.0.
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Re: [fpc-devel] Unreachable code warnings
Joao Morais wrote: The compiler warns that the result wasn't assigned, but that function's result simply cannot be reached. Why not make it a procedure ? Micha ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
Micha Nelissen wrote: Joao Morais wrote: The compiler warns that the result wasn't assigned, but that function's result simply cannot be reached. Why not make it a procedure ? Because it is an abstract method. -- Joao Morais ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Unreachable code warnings
Florian Klaempfl wrote:
Joao Morais schrieb:
The compiler warns that the result wasn't assigned, but that function's
result simply cannot be reached.
Fixed in trunk when compiled with -Oodfa which will be probably a
default in 2.4.0.
Thanks. Now a note:
{$mode objfpc}
var
vobj: tclass;
vmethod: function: string of object;
begin
vobj := tobject;
vmethod := @vobj.classname;
writeln(vmethod);
end.
Remove the comment and the note is also removed.
--
Joao Morais
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Re: [fpc-devel] Unreachable code warnings
Joao Morais wrote: Remove the comment and the note is also removed. sed 's/^Remove.*//' -- Joao Morais ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
