[NewPM] Set -enable-npm-optnone to true by default

[aeubanks]

Summary

This makes the NPM skip not required passes on functions marked optnone.

If this causes a pass that should be required but has not been marked
required to be skipped, add
static bool isRequired() { return true; }
to the pass class. AlwaysInlinerPass is an example.

clang/test/CodeGen/O0-no-skipped-passes.c is useful for checking that
no passes are skipped under -O0.

The -enable-npm-optnone option will be removed once this has been stable
for long enough without issues.

[aeubanks]

ping?

[asbirlea]

Could you add a few lines about this in the LLVM documentation?
We've had all the discussion in patches, so it may get unnoticed if it's not documented.

[aeubanks]

In D87869#2295655, @asbirlea wrote:

Could you add a few lines about this in the LLVM documentation?
We've had all the discussion in patches, so it may get unnoticed if it's not documented.

Do you mean create new documentation? Or add to the documentation I wrote recently on writing NPM passes?
And do you mean writing up the part about adding isRequired() for passes that shouldn't be skipped? Or something specific about optnone?

[asbirlea]

Add to the documentation on NPM passes.
I meant to add about isRequired, but with mentioning the behavior for optnone functions. I didn't mean to document what optnone means.

[aeubanks]

Documentation done in https://reviews.llvm.org/D88342

[aeubanks]

Ping

[ychen]

LGTM

[asbirlea]

Thank you, and sorry for the delays in reviews.

llvm/lib/Passes/StandardInstrumentations.cpp

 #include "llvm/Support/raw_ostream.h"
 #include <unordered_set>
 #include <vector>
 
 using namespace llvm;
 
 // TODO: remove once all required passes are marked as such.
 static cl::opt<bool>
-    EnableOptnone("enable-npm-optnone", cl::init(false),
+    EnableOptnone("enable-npm-optnone", cl::init(true),
                   cl::desc("Enable skipping optional passes optnone functions "
                            "under new pass manager"));
 
 cl::opt<bool> PreservedCFGCheckerInstrumentation::VerifyPreservedCFG(
     "verify-cfg-preserved", cl::Hidden,
 #ifdef NDEBUG
     cl::init(false));
 #else