From 16a50c9e642fd085e5ceb68c403b71b5b2e0607c Mon Sep 17 00:00:00 2001
From: River Riddle <riddleriver@gmail.com>
Date: Tue, 23 Feb 2021 16:40:09 -0800
Subject: [PATCH] [mlir][Inliner] Keep the number of async pass managers
 constant

This prevents a bug in the pass instrumentation implementation where the main thread would end up with a different pass manager in different runs of the pass.
---
 mlir/lib/Transforms/Inliner.cpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mlir/lib/Transforms/Inliner.cpp b/mlir/lib/Transforms/Inliner.cpp
index ad89e47715085..0a2cc7eb4c98a 100644
--- a/mlir/lib/Transforms/Inliner.cpp
+++ b/mlir/lib/Transforms/Inliner.cpp
@@ -687,10 +687,10 @@ LogicalResult
 InlinerPass::optimizeSCCAsync(MutableArrayRef<CallGraphNode *> nodesToVisit,
                               MLIRContext *context) {
   // Ensure that there are enough pipeline maps for the optimizer to run in
-  // parallel.
-  size_t numThreads =
-      std::min((size_t)llvm::hardware_concurrency().compute_thread_count(),
-               nodesToVisit.size());
+  // parallel. Note: The number of pass managers here needs to remain constant
+  // to prevent issues with pass instrumentations that rely on having the same
+  // pass manager for the main thread.
+  size_t numThreads = llvm::hardware_concurrency().compute_thread_count();
   if (opPipelines.size() < numThreads) {
     // Reserve before resizing so that we can use a reference to the first
     // element.