[Coverage] Speed up function record iteration (#122050)

When iterating over function records, filtered by file name, currently,
the iteration goes over all the function records, repeatedly for each
source file, essentially giving quadratic behavior.

413647d730972eac9675f695c2ea63fb393a5531 sped up some cases by keeping
track of the indices of the function records corresponding to each file
name. This change expands the use of that map to FunctionRecordIterator.

On a test case with Firefox's libxul.so and a 2.5MB profile, this brings
down the runtime of `llvm-cov export $lib --instr-profile $prof -t lcov`
from 12 minutes with 90% spent in skipOtherFiles to 19 seconds with no
samples in skipOtherFiles at all under a sampling profiler (with a
sampling interval of 1ms).

Fixes #62079

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
index 6d6678e..c395856 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
@@ -618,7 +618,7 @@ unsigned CounterMappingContext::getMaxCounterID(const Counter &C) const {
 void FunctionRecordIterator::skipOtherFiles() {
   while (Current != Records.end() && !Filename.empty() &&
          Filename != Current->Filenames[0])
-    ++Current;
+    advanceOne();
   if (Current == Records.end())
     *this = FunctionRecordIterator();
 }