Extended Description

Clang "CodeGen Function" timers from -ftime-trace for some functions falls outside of the "Frontend" timer and thus between Frontend and Backend (see attached screenshot). I think this should be counted under Frontend. In the original motivating example the time between "Frontend" and "Backend" was 11% of the overall execution time so fairly significant.

e.g. at r361164

Apply patch to trace ALL durations however small (to allow small reproducible)

diff --git a/llvm/lib/Support/TimeProfiler.cpp b/llvm/lib/Support/TimeProfiler.cpp
index bc234081564..f63847a8a28 100644
--- a/llvm/lib/Support/TimeProfiler.cpp
+++ b/llvm/lib/Support/TimeProfiler.cpp
@@ -65,8 +65,8 @@ struct TimeTraceProfiler {
E.Duration = steady_clock::now() - E.Start;

 // Only include sections longer than TimeTraceGranularity msec.

• if (duration_cast(E.Duration).count() > TimeTraceGranularity)

•  Entries.emplace_back(E);
  

• //if (duration_cast(E.Duration).count() > TimeTraceGranularity)

• Entries.emplace_back(E);

  // Track total time taken by each "name", but only the topmost levels of
  // them; e.g. if there's a template instantiation that instantiates other

$ cat test.cpp
template void foo(T) {}
void bar() { foo(0); }
$ clang -c -ftime-trace test.cpp

test.json now has CodeGen Function for foo between "Frontend" and "Backend"

{
"traceEvents": [
...
{
"args": {
"detail": ""
},
"dur": 1451,
"name": "Frontend",
"ph": "X",
"pid": 1,
"tid": 0,
"ts": 3722
},
{
"args": {
"detail": "foo"
},
"dur": 66,
"name": "CodeGen Function",
"ph": "X",
"pid": 1,
"tid": 0,
"ts": 5177
},
...
{
"args": {
"detail": ""
},
"dur": 2866,
"name": "Backend",
"ph": "X",
"pid": 1,
"tid": 0,
"ts": 5287
},
...
}