[llvm-bugs] [Bug 42580] New: missed optimization leading to compiletime assert with address sanitizer

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42580

            Bug ID: 42580
           Summary: missed optimization leading to compiletime assert with
                    address sanitizer
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: arnd at linaro.org
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

The current clang-9 prerelease causes one file in the linux kernel to get fail
compilation with an assertion triggering when building with
-sanitize=kernel-address:

void __iwl_err(char *, ...);
int a;
void iwl_fw_dbg_apply_point() {
  const char b[] = "WRT ext=%d. Invalid apply point %d for %s\n";
  if (a) {
    void __compiletime_assert_2790(void);
    if (b[sizeof(b) - 2] != '\n')
      __compiletime_assert_2790();
  }
  __iwl_err(0, b);
}

$ clang-9 -O2 -fsanitize=kernel-address  -S dbg.i -o-    | grep compiletime
        callq   __compiletime_assert_2790

both clang-8 and gcc-8 pass the assertion here.

See also https://godbolt.org/z/cPrkv4

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