Index: lib/Passes/PassBuilder.cpp
===================================================================
--- lib/Passes/PassBuilder.cpp
+++ lib/Passes/PassBuilder.cpp
@@ -155,10 +155,11 @@
 
 static cl::opt<unsigned> MaxDevirtIterations("pm-max-devirt-iterations",
                                              cl::ReallyHidden, cl::init(4));
+
 static cl::opt<bool>
-    RunPartialInlining("enable-npm-partial-inlining", cl::init(false),
+    RunPartialInliningThinLTOPreLink("enable-npm-lto-prelink-partial-inlining", cl::init(true),
                        cl::Hidden, cl::ZeroOrMore,
-                       cl::desc("Run Partial inlinining pass"));
+                       cl::desc("Run Partial inlining pass during thinLTO prelink"));
 
 static cl::opt<bool>
     RunNewGVN("enable-npm-newgvn", cl::init(false),
@@ -691,8 +692,7 @@
 
   // Run partial inlining pass to partially inline functions that have
   // large bodies.
-  if (RunPartialInlining)
-    MPM.addPass(PartialInlinerPass());
+  MPM.addPass(PartialInlinerPass());
 
   // Remove avail extern fns and globals definitions since we aren't compiling
   // an object file for later LTO. For LTO we want to preserve these so they
@@ -861,7 +861,7 @@
   // phase that will run after the thin link, running this here ends up with
   // less information than will be available later and it may grow functions in
   // ways that aren't beneficial.
-  if (RunPartialInlining)
+  if (RunPartialInliningThinLTOPreLink)
     MPM.addPass(PartialInlinerPass());
 
   // Reduce the size of the IR as much as possible.
Index: lib/Transforms/IPO/PassManagerBuilder.cpp
===================================================================
--- lib/Transforms/IPO/PassManagerBuilder.cpp
+++ lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -44,8 +44,9 @@
 using namespace llvm;
 
 static cl::opt<bool>
-    RunPartialInlining("enable-partial-inlining", cl::init(false), cl::Hidden,
-                       cl::ZeroOrMore, cl::desc("Run Partial inlinining pass"));
+    RunPartialInliningThinLTOPreLink("enable-lto-prelink-partial-inlining", cl::init(false),
+                       cl::Hidden, cl::ZeroOrMore,
+                       cl::desc("Run Partial inlining pass during thinLTO prelink"));
 
 static cl::opt<bool>
     RunLoopVectorization("vectorize-loops", cl::Hidden,
@@ -517,7 +518,9 @@
   // we must insert a no-op module pass to reset the pass manager.
   MPM.add(createBarrierNoopPass());
 
-  if (RunPartialInlining)
+  // Only run partial inlining when we're either i) not preparing for thinLTO,
+  // or ii) preparing for thinLTO AND we've turned on the CL option.
+  if (!PrepareForThinLTO || (PrepareForThinLTO && RunPartialInliningThinLTOPreLink))
     MPM.add(createPartialInliningPass());
 
   if (OptLevel > 1 && !PrepareForLTO && !PrepareForThinLTO)