continue in __finally fails assert (!BreakContinueStack.empty() && "continue stmt not in a loop)

[jaykrell]

int main()
{
    int a = 10;
    while (1)
    {
        __try {
            a = 20;
            *(volatile char*)0;
            a = 30;
        }
        __finally
        {
            // Next line is not needed.
            //a = _abnormal_termination() ? 40 : 50;
        
            //goto A;
        
            continue;
        }
    }

A:
    return a;
}

/*
1.c(18,13): warning: jump out of __finally block has undefined behavior [-Wjump-seh-finally]
break;;
^
Assertion failed: !BreakContinueStack.empty() && "continue stmt not in a loop!", file C:\Users\swift-ci\jenkins\workspace\oss-swift-windows-toolchain\llvm-project\clang\lib\CodeGen\CGStmt.cpp, line 1402
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:

1. parser at end of file
2. 1.c:1:5: LLVM IR generation of declaration 'main'
3. 1.c:1:5: Generating code for declaration 'main'
4. 1.c:5:5: LLVM IR generation of compound statement ('{}')
5. 1.c:12:9: LLVM IR generation of compound statement ('{}')
   */

[jaykrell]

More information.
The Visual C++ warning has meaning, in that, you can continue once from the exception, but not after that. I wonder if it has locally unwound, vs. duplicated the loop in the finally block. We can find out, step, disassemble, print RIP, etc.

So the first example does return 0xC0000005. I wrote the second example to explore a more states, while avoiding that.

C:\s>type continue-in-finally.c
int main()
{
    int a = 10;
    while (a < 100)
    {
        __try {
            a += 10;
printf("1\n");
            *(volatile char*)0;
printf("2\n");
            a += 10;
        }
        __finally
        {
printf("3\n");
            continue;
        }
    }
printf("4\n");
    return a;
}
C:\s>cl continue-in-finally.c && continue-in-finally.exe
Microsoft (R) C/C++ Optimizing Compiler Version 19.41.34123 for x64
continue-in-finally.c(16): warning C4532: 'continue': jump out of __finally block has undefined behavior 
1
3
1

C:\s>echo %errorlevel%
-1073741819

C:\s>type continue-in-finally-once.c
#include "excpt.h"
int main()
{
    int alternate = 0;
    int once = 0;
    int a = 10;
    while (a < 50) {
        __try {
            a += 10;
printf("1 %d\n", a);
            if (a == 20)
                *(volatile char*)0;
printf("2 %d\n", a);
            a += 10;
        }
        __finally
        {
printf("3 %d\n", a);
            ++alternate;
            if (++once == 1 || (AbnormalTermination() || (alternate & 1))) {
                printf("=> continue\n");
                continue;
            } else {
                printf("=> no continue\n");
            }
printf("4 %d\n", a);
        }
    }
printf("5 %d\n", a);
    return a;
}
C:\s>cl continue-in-finally-once.c && continue-in-finally-once.exe
Microsoft (R) C/C++ Optimizing Compiler Version 19.41.34123 for x64
continue-in-finally-once.c(22): warning C4532: 'continue': jump out of __finally block has undefined behavior during termination handling


1 20
3 20
=> continue
1 30
2 30
3 40
=> no continue
4 40
1 50
2 50
3 60
=> continue
5 60

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Jay Krell (jaykrell)

``` int main() { int a = 10; while (1) { __try { a = 20; *(volatile char*)0; a = 30; } __finally { // Next line is not needed. //a = _abnormal_termination() ? 40 : 50;

        //goto A;
    
        continue;
    }
}

A:
return a;
}

/*
1.c(18,13): warning: jump out of __finally block has undefined behavior [-Wjump-seh-finally]
            break;;
            ^
Assertion failed: !BreakContinueStack.empty() && "continue stmt not in a loop!", file C:\Users\swift-ci\jenkins\workspace\oss-swift-windows-toolchain\llvm-project\clang\lib\CodeGen\CGStmt.cpp, line 1402
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:

1. <eof> parser at end of file
2. 1.c:1:5: LLVM IR generation of declaration 'main'
3. 1.c:1:5: Generating code for declaration 'main'
4. 1.c:5:5: LLVM IR generation of compound statement ('{}')
5. 1.c:12:9: LLVM IR generation of compound statement ('{}')
*/

</details>