https://bugs.llvm.org/show_bug.cgi?id=37676
Bug ID: 37676
Summary: Intermittent bug in opt with -O3 -newgvn
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: -New Bugs
Assignee: unassignedclangbugs at nondot.org
Reporter: Vsevolod.Livinskij at frtk.ru
CC: llvm-bugs at lists.llvm.org
Created attachment 20388
--> https://bugs.llvm.org/attachment.cgi?id=20388&action=edit
Reproducer.
Intermittent bug in opt with -O3 -newgvn.
It gives 2 variants of assembler for different compilations.
opt-bisect-limit points to "Global Value Numbering on function"
Reproducer:
>$ cat func.c
extern unsigned long long b, e, g;
extern const signed char a;
extern const unsigned c;
extern unsigned d, h;
extern signed char f, i;
extern unsigned *j;
extern unsigned long long *k;
extern signed char *l;
void foo() {
if (*k <= (8 & -b * ((1 - 8ULL) * c) ?: ~i))
f = 8 & -(b * ((1 - 8ULL) * c)) ?: i * d;
e = g ? -(8 & -b * ((1 - 8ULL) * c) ?: i * d) : 0;
if (!a) {
*l = ~0 ? 8 & -(b * ((1 - 8ULL) * c)) ?: i * d : 2022409665839104;
h = 8 & -(b * ((1ULL - 8) * c)) ? b * ((1 - 8ULL) * c) : 0;
}
if (8 & -(b * ((1ULL - 8) * c)) ? 0 : ~0)
*j = b * ((1 - 8ULL) * c);
}
>$ cat driver.c
#include <stdio.h>
unsigned long long b, e, g;
const signed char a = 8;
const unsigned c = 92620;
unsigned d, h, m;
signed char f, i;
unsigned *j = &m;
unsigned long long *k = &e;
signed char *l;
void foo();
int main() {
*j = 42;
foo();
printf("%u\n", *j);
}
Error:
>$ clang driver.c func.c
>$ ./a.out
0
>$ clang -O3 -Xclang -disable-llvm-optzns -emit-llvm -c -o func.bc func.c
>$ opt -O3 -o func.ll func.bc -newgvn
>$ clang -O3 -c -o func.o func.ll
>$ clang -O3 driver.c func.o
>$ ./a.out
42
LLVM version:
clang version 7.0.0 (trunk 333836)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /users/vlivinsk/llvm/bin-trunk/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
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