[PATCH v2] implement -Winfinite-recursion [PR88232]

Martin Sebor msebor@gmail.com
Thu Nov 11 21:46:46 GMT 2021

Attached is a v2 of the solution I posted earlier this week
with a few tweaks made after a more careful consideration of
the problem and possible false negatives and positives.

1) It avoids warning for [apparently infinitely recursive] calls
    in noreturn functions where the recursion may be prevented by
    a call to a noreturn function.
2) It avoids warning for calls where the recursion may be prevented
    by a call to a longjmp or siglongjmp.
3) It warns for recursive calls to built-ins in definitions of
    the corresponding library functions (e.g., for a call to
    __builtin_malloc in malloc).
4) It warns for calls to C++ functions even if they call other
    functions that might throw and so break out of the infinite
    recursion.  (E.g., operator new.)  This is the same as Clang.
5) It doesn't warn for calls to C++ functions with the throw

Besides these changes to the warning itself, I've also improved
the code a bit by making the workhorse function a member of
the pass so recursive calls don't need to pass as many arguments
to itself.

Retested on x86_64-linux and by building Glibc and Binutils/GDB.

A possible enhancement is to warn for calls to calloc, malloc,
or realloc from within the definition of one of the other two
functions.  That might be a mistake made in code that tries
naively to replace the allocator with its own implementation.

On 11/9/21 9:28 PM, Martin Sebor wrote:
> The attached patch adds support to the middle end for detecting
> infinitely recursive calls.  The warning is controlled by the new
> -Winfinite-recursion option.  The option name is the same as
> Clang's.
> I scheduled the warning pass to run after early inlining to
> detect mutually recursive calls but before tail recursion which
> turns some recursive calls into infinite loops and so makes
> the two indistinguishable.
> The warning detects a superset of problems detected by Clang
> (based on its tests).  It detects the problem in PR88232
> (the feature request) as well as the one in PR 87742,
> an unrelated problem report that was root-caused to bug due
> to infinite recursion.
> This initial version doesn't attempt to deal with superimposed
> symbols, so those might trigger false positives.  I'm not sure
> that's something to worry about.
> The tests are very light, but those for the exceptional cases
> are exceedingly superficial, so it's possible those might harbor
> some false positives and negatives.
> Tested on x86_64-linux.
> Martin

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