[llvm-bugs] [Bug 49475] New: compile-time explosion with assumes at -O1

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49475

            Bug ID: 49475
           Summary: compile-time explosion with assumes at -O1
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: haoxintu at gmail.com
                CC: llvm-bugs at lists.llvm.org

Hi, all.

This program, small.c, makes Clang-trunk hung on with -O1 at compile time.

$cat small.c
#include <stdint.h>
int a;
void b() {
  int c;
  uint16_t d;
  uint64_t e;
  if (d = a) {
    uint8_t *f;
    for (;;) {
      for (; *f;)
        f = &d;
      uint8_t g = &e;
    }
  }
  for (;;) {
    int8_t i;
    int32_t j;
    int64_t k;
    if (a) {
      int64_t *l = &e;
      j = e - (*l = 0);
      for (; i; i++) {
        int32_t *m = &j;
        k ^= a & (5 ? j || d : 0);
        if (d |= (k |= e &= a) >= i - *m)
          for (c = 3; c; c)
            ;
      }
    }
  }
}

$clang -w -c -O1 small.c
//endless compiling

#clang -v
clang version 13.0.0 (https://github.com/llvm/llvm-project
a968e7b82eac364d411c81aae58722a0b3a4b29c)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir:
/home/haoxin/haoxin-data/dut-research/compilers/llvm-project/build-20210304/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Candidate multilib: .;@m64
Selected multilib: .;@m64

Thanks,
Haoxin

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