Move LowerTypeTestsPass after inlining in ThinLTO pipeline

[dmikulin]

Summary

LowerTypeTestsPass runs early in the ThinLTO pipeline, which prevents post-inline optimizations to eliminate unnecessary type checks.

llvm/lib/Transforms/IPO/PassManagerBuilder.cpp

void PassManagerBuilder::populateModulePassManager(
   // FIXME: This is a HACK! The inliner pass above implicitly creates a CGSCC
   // pass manager that we are specifically trying to avoid. To prevent this
   // we must insert a no-op module pass to reset the pass manager.
   MPM.add(createBarrierNoopPass());
 
   if (RunPartialInlining)
     MPM.add(createPartialInliningPass());
 
+  if (ImportSummary) {
+    // Run this pass after inlining as it creates more opportunities to
+    // eliminate type checks.
+    MPM.add(createLowerTypeTestsPass(nullptr, ImportSummary));
+  }
+
   if (OptLevel > 1 && !PrepareForLTO && !PrepareForThinLTO)
     // Remove avail extern fns and globals definitions if we aren't
     // compiling an object file for later LTO. For LTO we want to preserve
     // these so they are eligible for inlining at link-time. Note if they
     // are unreferenced they will be removed by GlobalDCE later, so
     // this only impacts referenced available externally globals.
     // Eventually they will be suppressed during codegen, but eliminating
     // here enables more opportunity for GlobalDCE as it may make

 void PassManagerBuilder::populateThinLTOPassManager(
     legacy::PassManagerBase &PM) {
   PerformThinLTO = true;
 
   if (VerifyInput)
     PM.add(createVerifierPass());
 
   if (ImportSummary) {
-    // These passes import type identifier resolutions for whole-program
-    // devirtualization and CFI. They must run early because other passes may
-    // disturb the specific instruction patterns that these passes look for,
+    // This pass imports type identifier resolutions for whole-program
+    // devirtualization. It must run early because other passes may
+    // disturb the specific instruction patterns that this pass looks for,
     // creating dependencies on resolutions that may not appear in the summary.
     //
     // For example, GVN may transform the pattern assume(type.test) appearing in
     // two basic blocks into assume(phi(type.test, type.test)), which would
     // transform a dependency on a WPD resolution into a dependency on a type
     // identifier resolution for CFI.
     //
     // Also, WPD has access to more precise information than ICP and can
     // devirtualize more effectively, so it should operate on the IR first.
     PM.add(createWholeProgramDevirtPass(nullptr, ImportSummary));
-    PM.add(createLowerTypeTestsPass(nullptr, ImportSummary));
   }
 
   populateModulePassManager(PM);
 
   if (VerifyOutput)
     PM.add(createVerifierPass());
   PerformThinLTO = false;
 }