https://bugs.llvm.org/show_bug.cgi?id=35577
Bug ID: 35577
Summary: [Clang-optimization] wrong code on incremental
operator in a loop
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: -New Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: yangyib...@nju.edu.cn
CC: llvm-bugs@lists.llvm.org
$ clang -v
clang version 6.0.0-svn319838-1~exp1 (trunk)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.2.0
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0
Candidate multilib: .;@m64
Selected multilib: .;@m64
$ cat small.c
int printf(const char *, ...);
union {
short a;
long b;
} c;
short *d = &c.a;
int e = 0;
long *f = &c.b;
int main() {
for (; e <= 1; e++) {
*f = 0;
++*d;
}
printf("%d\n", c.a);
}
$ clang -O0 small.c; ./a.out
1
$ clang -Ofast small.c; ./a.out
2
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