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From: "zhan3299 at purdue dot edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/99156] New: __builtin_expect affects the interpretation of its first operand
Date: Fri, 19 Feb 2021 04:29:22 +0000 [thread overview]
Message-ID: <bug-99156-4@http.gcc.gnu.org/bugzilla/> (raw)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99156
Bug ID: 99156
Summary: __builtin_expect affects the interpretation of its
first operand
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: zhan3299 at purdue dot edu
Target Milestone: ---
I hope it does not bother. I try to refer to a bug in llvm which may also
affect gcc.
Following are copied-and-pasted from the discussion about a similar bug in
clang (https://bugs.llvm.org/show_bug.cgi?id=49239#c3).
Specifically,
> int maybe_vla(int n) {
> goto label;
> int arr[({0;})];
> label:
> return sizeof(arr);
> }
>
> ... is rejected by both Clang and GCC because the statement-expression is not an ICE, but
>
> int maybe_vla(int n) {
> goto label;
> int arr[__builtin_expect(({0;}), 0)];
> label:
> return sizeof(arr);
> }
>
> ... is accepted. This seems like a bug in both compilers to me: __builtin_expect isn't supposed to affect the interpretation of its first operand, and presumably shouldn't be weakening the strict ICE checks.
case 1: https://godbolt.org/z/zWGEfx
case 2: https://godbolt.org/z/bejfcc
next reply other threads:[~2021-02-19 4:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-19 4:29 zhan3299 at purdue dot edu [this message]
2021-02-19 15:15 ` [Bug c/99156] " marxin at gcc dot gnu.org
2021-02-19 21:32 ` zhan3299 at purdue dot edu
2021-07-23 18:18 ` [Bug c/99156] __builtin_expect is folded too soon allowing an non-integer-constant-expr to become an integer-const-expr pinskia at gcc dot gnu.org
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