<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/63676>63676</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            FlameGraphs incorrect from `llvm-xray stack --stack-format=flame`
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          DerickEddington
      </td>
    </tr>
</table>

<pre>
    ## Summary

The numeric values produced by `llvm-xray stack --stack-format=flame --aggregation-type=time --all-stacks` are incorrect because they are the total amount of time spent in each function, but [`flamegraph.pl`](https://github.com/brendangregg/FlameGraph) needs these values to instead be only the amount of time spent directly in each function excluding any time spent in functions called by a function, because `flamegraph.pl` does its own summing of each's total time.

## Description

For the [reproducible example program](#reproducible-example) given farther below:

The incorrect output is like:
```
main; 17797754976
main;f2; 5925051360
main;f2;busy; 5925047168
main;f1; 5941978880
main;f1;busy; 5941971904
main;busy; 5930714592
```
Which renders as an incorrect graph:

But correct output would be like:
```
main; 10144
main;f2; 4192
main;f2;busy; 5925047168
main;f1; 6976
main;f1;busy; 5941971904
main;busy; 5930714592
```
Which renders as the correct graph:

I.e., only leafs should have their total amount of time, and non-leafs should have the difference between their total and the sum of all their children's totals, because `flamegraph.pl` itself will sum each non-leaf's value with its descendents' values for showing each non-leaf's total amount of time.

<details>

<summary>More precisely: <i>(click to expand)</i></summary>

```
bad-val(STACK) = total(STACK)
total(STACK) = exit(STACK) - enter(STACK)

bad-val(main) =  17797754976 = exit(main) - enter(main)
enter(main) = 69839874297664
exit(main)  = 69857672052640

bad-val(main;f1) =   5941978880 = exit(main;f1) - enter(main;f1)
enter(main;f1) = 69845805019744
exit(main;f1)  = 69851746998624

...
```
```
good-val(STACK) = total(STACK) - child-sum(STACK)
child-sum(STACK) = total(STACK;CHILD-1) + ... + total(STACK;CHILD-N)

good-val(main) = 10144 = total(main) - child-sum(main)
child-sum(main) = total(main;busy) + total(main;f1) + total(main;f2)
                =       5930714592 +     5941978880 + 5925051360
                =   good-val(main;busy)
                  + good-val(main;f1) + good-val(main;f1;busy)
                  + good-val(main;f2) + good-val(main;f2;busy)

child-sum(main;busy) = 0
child-sum(main;f1) = total(main;f1;busy)
child-sum(main;f2) = total(main;f2;busy)
child-sum(main;f1;busy) = 0
child-sum(main;f2;busy) = 0

...
```
(Hopefully, I didn't screw that up.  I think you'll get the idea.)

</details>

## Reproducible Example

#### `main.c` file
```c
static void busy(void) { for (unsigned i = 4000000000; i > 0; i--) ; }
static void f1(void) { busy(); }
static void f2(void) { busy(); }
int main(void) { busy(); f1(); f2(); }
```

#### Build, run, and generate
```shell
clang -O0 -fxray-instrument -fxray-instruction-threshold=1 main.c -o main
```
```shell
XRAY_OPTIONS="patch_premain=true xray_mode=xray-basic verbosity=1" ./main
```
```shell
X=xray-log.main.$YOURS

llvm-xray stack --stack-format=flame --aggregation-type=time --all-stacks \
 --instr_map=./main $X > $X.flame

flamegraph.pl $X.flame > $X.svg
```

Note: I've also had some other similarly incorrect flame-graphs from my much more complicated programs, that were compiled without `-fxray-instruction-threshold=$T` (i.e. where that threshold was the default larger one), but I didn't analyze their (much more complicated) flame output to prove the incorrectness for those.

## Versions

```
$ llvm-xray --version
LLVM (http://llvm.org/):
 LLVM version 16.0.6
  Optimized build.
```
```
$ clang --version
clang version 16.0.6
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /nix/store/b3qg3lglka8s298plxfkhlaifw5njv5c-clang-16.0.6/bin
```
(Both installed via the [NixOS packages](https://github.com/NixOS/nixpkgs) `llvmPackages_16.libllvm` and `clang_16` (from the `unstable` channel, to have the latest version `16.0.6`).)

Version of `flamegraph.pl`: `d9fcc272b6a08c3e3e5b7919040f0ab5f8952d65` (Git commit of repo).
</pre>
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