[llvm-bugs] [Bug 46124] New: Clang stop detecting UBs after a divide by zero

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46124

            Bug ID: 46124
           Summary: Clang stop detecting UBs after a divide by zero
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: haoxintu at gmail.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

This code test1.cc

#include<iostream>
int main () {
    int a = 1;
    for (int i = 0; i < 10; ++i) {
        a /= i; // Error: division by zero on the first iteration
    }

    int b = 0;
    int bb = 0 / b;
    0 / 0;
    std::cout << "ok" << std::endl;
    return 0;
}

$clang++-trunk -w -fsanitize=integer-divide-by-zero test1.cc ; ./a.out 
test1.cc:5:11: runtime error: division by zero
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior example.cpp:5:11 in 
UndefinedBehaviorSanitizer:DEADLYSIGNAL
==1==ERROR: UndefinedBehaviorSanitizer: FPE on unknown address 0x000000431817
(pc 0x000000431817 bp 0x7fff88ddde50 sp 0x7fff88ddde20 T1)
    #0 0x431817  (/app/output.s+0x431817)
    #1 0x7f56e7e59b96  (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #2 0x4031e9  (/app/output.s+0x4031e9)
UndefinedBehaviorSanitizer can not provide additional info.
SUMMARY: UndefinedBehaviorSanitizer: FPE (/app/output.s+0x431817) 
==1==ABORTING

Clang only detects one runtime error in for statement but leaves out detecting
the statements following ones.

In test2.cc

#include<iostream>
int main () {
    /*
    int a = 1;
    for (int i = 0; i < 10; ++i) {
        a /= i; // Error: division by zero on the first iteration
    }
    */

    int b = 0;
    int bb = 0 / b;
    0 / 0;
    std::cout << "ok" << std::endl;
    return 0;
}
$clang++-trunk -fsanitize=integer-divide-by-zero test2.cc ; ./a.out 
test2.cc:11:16: runtime error: division by zero
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior example.cpp:11:16 in 
UndefinedBehaviorSanitizer:DEADLYSIGNAL
==1==ERROR: UndefinedBehaviorSanitizer: FPE on unknown address 0x0000004317fd
(pc 0x0000004317fd bp 0x7ffd6c2922f0 sp 0x7ffd6c2922d0 T1)
    #0 0x4317fd  (/app/output.s+0x4317fd)
    #1 0x7fe566be1b96  (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #2 0x4031e9  (/app/output.s+0x4031e9)
UndefinedBehaviorSanitizer can not provide additional info.
SUMMARY: UndefinedBehaviorSanitizer: FPE (/app/output.s+0x4317fd) 
==1==ABORTING

In gcc-trunk
$./g++ -w -fsanitize=integer-divide-by-zero test2.cc ; ./a.out 
test.cc:11:16: runtime error: division by zero
test.cc:12:7: runtime error: division by zero
ok

Should the main function return from "return 0" rather than exit directly from
the for statement?

I also file a bug report in GCC, they confirmed this limitation immediately.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95385

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