https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112296
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |documentation
CC| |jsm28 at gcc dot gnu.org,
| |rth at gcc dot gnu.org
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
+FAIL: gcc.c-torture/execute/bcp-1.c -O1 (test for excess errors)
+UNRESOLVED: gcc.c-torture/execute/bcp-1.c -O1 compilation failed to produce
executable
that's because
bcp-1.c:(.text+0x6c): undefined reference to `func'^M
collect2: error: ld returned 1 exit status^M
the testcase can be reduced to
int func(void);
int bad7(void) { return __builtin_constant_p(func()); }
and we want the side-effect to disappear!? There's more fun in this testcase,
like verifying that
int bad1(void) { return __builtin_constant_p(global++); }
returns 0 (but not verifying whether 'global' is altered or not).
I don't see it documented that __builtin_constant_p discards side-effects on
operands - that would in fact make it behave like 'constexpr'?!
commit 54303b5cb3076f7bae9102c08b59d57b1a9f5104
Author: Richard Henderson <r...@cygnus.com>
Date: Tue Jul 7 06:41:17 1998 -0700
* gcc.c-torture/execute/bcp-1.c: New test.
So this also becomes a documentation thing and I doubt we can start to
retain side-effects we've thrown away for decades now. But then
relying on _folding_ to implement what becomes a language extension this
way is definitely error-prone and fragile.
I think we should also definitely diagnose this somehow (which would also
mean moving discarding of side-effects to the frontend(s)).
Joseph, Richard, do you have anything to add or remember discussions about
this semantic detail of __builtin_constant_p?
