[Inlining] Add PreInlineThreshold for the new pass manager

[kazu]

Summary

This patch makes it easy to try out different preinlining thresholds
with a command-line switch just like -preinline-threshold for the
legacy pass manager.

[davidxl]

lgtm

llvm/lib/Passes/PassBuilder.cpp

 
 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),
                        cl::Hidden, cl::ZeroOrMore,
                        cl::desc("Run Partial inlinining pass"));
 
+static cl::opt<int> PreInlineThreshold(
+    "npm-preinline-threshold", cl::Hidden, cl::init(75), cl::ZeroOrMore,
+    cl::desc("Control the amount of inlining in pre-instrumentation inliner "
+             "(default = 75)"));
+
 static cl::opt<bool>
     RunNewGVN("enable-npm-newgvn", cl::init(false),
               cl::Hidden, cl::ZeroOrMore,
               cl::desc("Run NewGVN instead of GVN"));
 
 static cl::opt<bool> EnableGVNHoist(
     "enable-npm-gvn-hoist", cl::init(false), cl::Hidden,
     cl::desc("Enable the GVN hoisting pass for the new PM (default = off)"));
void PassBuilder::addPGOInstrPasses(ModulePassManager &MPM, bool DebugLogging,
   // Generally running simplification passes and the inliner with an high
   // threshold results in smaller executables, but there may be cases where
   // the size grows, so let's be conservative here and skip this simplification
   // at -Os/Oz. We will not do this  inline for context sensistive PGO (when
   // IsCS is true).
   if (!isOptimizingForSize(Level) && !IsCS) {
     InlineParams IP;
 
-    // In the old pass manager, this is a cl::opt. Should still this be one?
-    IP.DefaultThreshold = 75;
+    IP.DefaultThreshold = PreInlineThreshold;
 
     // FIXME: The hint threshold has the same value used by the regular inliner.
     // This should probably be lowered after performance testing.
     // FIXME: this comment is cargo culted from the old pass manager, revisit).
     IP.HintThreshold = 325;
 
     CGSCCPassManager CGPipeline(DebugLogging);