[llvm-bugs] [Bug 49975] New: Missing variables after instcombine pass at O3

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49975

            Bug ID: 49975
           Summary: Missing variables after instcombine pass at O3
           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

Upon calling a function from an external module, the variable l_28 passed to it
is not visible from lldb. Using -opt-bisect-limit we discovered that the pass
causing the symbols disappear is "InstCombinePass".
Just like the one reported previously, the bug does not occur with lower
optimisation levels.


$ cat a.c
static short a = 4;
void  b( c)
{
short l_25 = 0;
int l_28,  l_35 = 2,  l_36 = 9,  l_37 = 5,  l_38 = 5,  l_69 =   (l_28 = a ) ==
0  & c   ;
test_nop();
test_support_3329(l_25, l_28, l_35, l_36, l_37, l_38, l_69);
}
int main ()
{
b( a)
;
a = 0;
}

$ cat lib/test.c
#include <stdio.h>
#include <stdint.h>
#include "test.h"

void test_nop() {
    printf("\n");
}

void test_support_3329(int l_25, int l_28, int l_35, int l_36, int l_37, int
l_38, int l_69) {
    printf("%d %d %d %d %d %d %d", l_25, l_28, l_35, l_36, l_37, l_38, l_69);
}
$ cat lib/test.h
#pragma once

void test_nop();
void test_support_3329(int l_25, int l_28, int l_35, int l_36, int l_37, int
l_38, int l_69);

$ 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 revision c2c977ce50597b0e5186afc342c5784bd0aa6973
lldb revision c2c977ce50597b0e5186afc342c5784bd0aa6973

$ clang -g -O3 -o opt lib/test.c a.c
$ lldb opt
(lldb) target create "opt"
Current executable set to
'/home/stepping/debuginfo-analysis/bug_submission/opt' (x86_64).
(lldb) b 7
Breakpoint 1: 2 locations.
(lldb) r
Process 26 launched: '/home/stepping/debuginfo-analysis/bug_submission/opt'
(x86_64)

Process 26 stopped
* thread #1, name = 'opt', stop reason = breakpoint 1.2
    frame #0: 0x00000000004005c9 opt`main [inlined] b at a.c:7:1
   4    short l_25 = 0;
   5    int l_28,  l_35 = 2,  l_36 = 9,  l_37 = 5,  l_38 = 5,  l_69 =   (l_28 =
a ) == 0  & c   ;
   6    test_nop();
-> 7    test_support_3329(l_25, l_28, l_35, l_36, l_37, l_38, l_69);
   8    }
   9    int main ()
   10   {
(lldb) frame var
(int) l_69 = 0
(int) l_38 = 5
(int) l_37 = 5
(int) l_36 = 9
(int) l_35 = 2
(short) l_25 = 0
(lldb) frame var l_28
error: no variable named 'l_28' found in this frame

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