[llvm-bugs] [Bug 52239] New: Variable's value not available from second loop iteration at Og

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=52239

            Bug ID: 52239
           Summary: Variable's value not available from second loop
                    iteration at Og
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: DebugInfo
          Assignee: unassignedbugs at nondot.org
          Reporter: cristianassaiante at outlook.com
                CC: jdevlieghere at apple.com, keith.walker at arm.com,
                    llvm-bugs at lists.llvm.org,
                    paul_robinson at playstation.sony.com

Variable l_143 value is not available at line 9 and 10 from the second loop
iteration, in fact it is only available at line 13 in the loop body.
>From bisect, this behavior may be caused by PostOrderFunctionAttrsPass on SCC
(f)

$ cat a.c
char a;
long b;
volatile int d;
char e(c) {
    return a;
}
void f() {
    int l_143 = 0;
    for (;
        b != 3;
        ++b) {
        l_143 = 0;
        l_143 = e(d);
    }
}
int main () {
    f();
}

$ clang -v
clang version 13.0.0
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
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/7.5.0
Candidate multilib: .;@m64
Selected multilib: .;@m64

$ lldb -v
lldb version 13.0.0

$ clang -g -Og -o opt a.c
(lldb) target create "opt"
Current executable set to '/home/stepping/56/reduce/opt' (x86_64).
(lldb) b 10
Breakpoint 1: 2 locations.
(lldb) run
Process 247 launched: '/home/stepping/56/reduce/opt' (x86_64)
Process 247 stopped
* thread #1, name = 'opt', stop reason = breakpoint 1.2
    frame #0: 0x00000000004004d0 opt`main [inlined] f at a.c:10:9
   7    void f() {
   8        int l_143 = 0;
   9        for (;
-> 10           b != 3;
   11           ++b) {
   12           l_143 = 0;
   13           l_143 = e(d);
(lldb) frame var
(int) l_143 = 0
(lldb) n
Process 247 stopped
* thread #1, name = 'opt', stop reason = step over
    frame #0: 0x00000000004004db opt`main [inlined] f at a.c:9:5
   6    }
   7    void f() {
   8        int l_143 = 0;
-> 9        for (;
   10           b != 3;
   11           ++b) {
   12           l_143 = 0;
(lldb) frame var
(int) l_143 = 0
(lldb) n
Process 247 stopped
* thread #1, name = 'opt', stop reason = step over
    frame #0: 0x00000000004004f0 opt`main [inlined] f at a.c:13:19
   10           b != 3;
   11           ++b) {
   12           l_143 = 0;
-> 13           l_143 = e(d);
   14       }
   15   }
   16   int main () {
(lldb) n
Process 247 stopped
* thread #1, name = 'opt', stop reason = step over
    frame #0: 0x00000000004004f6 opt`main [inlined] f at a.c:10:11
   7    void f() {
   8        int l_143 = 0;
   9        for (;
-> 10           b != 3;
   11           ++b) {
   12           l_143 = 0;
   13           l_143 = e(d);
(lldb) frame var
(int) l_143 = <variable not available>

(lldb) n
Process 247 stopped
* thread #1, name = 'opt', stop reason = step over
    frame #0: 0x00000000004004f9 opt`main [inlined] f at a.c:9:5
   6    }
   7    void f() {
   8        int l_143 = 0;
-> 9        for (;
   10           b != 3;
   11           ++b) {
   12           l_143 = 0;
(lldb) frame var
(int) l_143 = <variable not available>

(lldb) n
Process 247 stopped
* thread #1, name = 'opt', stop reason = step over
    frame #0: 0x00000000004004f0 opt`main [inlined] f at a.c:13:19
   10           b != 3;
   11           ++b) {
   12           l_143 = 0;
-> 13           l_143 = e(d);
   14       }
   15   }
   16   int main () {
(lldb) frame var
(int) l_143 = 0

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