[llvm-bugs] [Bug 49541] New: compile-time explosion with assumes at -O2 and -Os

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49541

            Bug ID: 49541
           Summary: compile-time explosion with assumes at -O2 and -Os
           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 code, small.c, is a valid program but makes Clang trunk hung on at compile
time at -O2 and -Os. Note that this issue also occurs in recently released
versions of clang, e.g., clang-10, clang-11.

$cat small.c
#include <stdint.h>
int a;
void b(int c) {
  int32_t *d = a;
  uint64_t e;
  int8_t f = 4;
  uint16_t g;
  if (0)
  j:
    if (e <= (*d *= a))
      goto j;
i:
  if (c ? g %= f : *d)
    goto i;
  goto j;
}

$clang -O2 -w small.c (or -Os)
//endless compiling

$clang -v
clang version 13.0.0 (https://github.com/llvm/llvm-project
590ac0a26af4c9f63d5564be8c13b12d409a7fd9)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir:
/home/haoxin/haoxin-data/dut-research/compilers/llvm-project/build-20210310/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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