[llvm-cov] Prevent llvm-cov from using too many threads

As reported here: https://reviews.llvm.org/D75153#1987272

Before, each instance of llvm-cov was creating one thread per hardware core, which wasn't needed probably because the number of inputs were small. This was probably causing a thread rlimit issue on large core count systems.

After this patch, the previous behavior is restored (to what was before rG8404aeb5):

If --num-threads is not specified, we create one thread per input, up to num.cores.
When specified, --num-threads indicates any number of threads, with no upper limit.

Differential Revision: https://reviews.llvm.org/D78408

1 files changed, 5 insertions, 4 deletions

diff --git a/llvm/lib/Support/Threading.cpp b/llvm/lib/Support/Threading.cpp
index 4bf373d..61f8ee5 100644
--- a/llvm/lib/Support/Threading.cpp
+++ b/llvm/lib/Support/Threading.cpp
@@ -84,14 +84,15 @@ void llvm::llvm_execute_on_thread_async(
 int computeHostNumHardwareThreads();
 
 unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
-  if (ThreadsRequested > 0)
-    return ThreadsRequested;
-
   int MaxThreadCount = UseHyperThreads ? computeHostNumHardwareThreads()
                                        : sys::getHostNumPhysicalCores();
   if (MaxThreadCount <= 0)
     MaxThreadCount = 1;
-  return MaxThreadCount;
+  if (ThreadsRequested == 0)
+    return MaxThreadCount;
+  if (!Limit)
+    return ThreadsRequested;
+  return std::min((unsigned)MaxThreadCount, ThreadsRequested);
 }
 
 namespace {