From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 8EAD73858C52; Tue,  5 Mar 2024 22:12:57 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 8EAD73858C52
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1709676777;
	bh=tNnF4EG28048+8V9+ZHB8GrxAncbvGrn5RWPPQ44W38=;
	h=From:To:Subject:Date:From;
	b=DXRGcgjnhSZ/tamlzLCM1kSm5XkWFWrhmhELN83TvsJWI//LEnC5voiqRrS5u92HN
	 MiHnR7SydKpxtkVAIgBPBlv1YZ8yAnRwuMUynXb5SQzjx9ZzIbbqegX8iMr0S9L3h4
	 mW1vwJoeJXI2g9dTEHpNY9fbEud5YAFoLUf2f2Cc=
From: "patrick at rivosinc dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/114247] New: RISC-V: miscompile at -O3
Date: Tue, 05 Mar 2024 22:12:57 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: patrick at rivosinc dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-114247-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114247

            Bug ID: 114247
           Summary: RISC-V: miscompile at -O3
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: patrick at rivosinc dot com
  Target Milestone: ---

Testcase:
int printf(const char *, ...);
union a {
  unsigned short b;
  int c;
  signed short d;
};
int e, f =3D 1, g;
long h;
const int **i;
void j(union a k, int l, unsigned m) {
  const int *a[100];
  i =3D &a[0];
  h =3D k.d;
}
static int o(union a k) {
  k.d =3D -1;
  while (1)
    if (f)
      break;
  j(k, g, e);
  return 0;
}
int main() {
  union a n =3D {1};
  o(n);
  printf("dec: %ld\n", h);
  printf("hex: %lX\n", h);
}

Commands:
> riscv64-unknown-linux-gnu-gcc -O3 red.c -o red.out -fno-strict-aliasing -=
fwrapv -fno-aggressive-loop-optimizations
> qemu-riscv64 red.out
dec: 65535
hex: FFFF

> riscv64-unknown-linux-gnu-gcc -O2 red.c -o red.out -fno-strict-aliasing -=
fwrapv -fno-aggressive-loop-optimizations
> qemu-riscv64 red.out
dec: -1
hex: FFFFFFFFFFFFFFFF

This testcase looks very suspect but AFAICT it doesn't contain any UB.

Found via fuzzer=