[Inliner] Don't skip inlining alwaysinline in optnone functions

[aeubanks]

Summary

Previously the NPM inliner would skip all potential inlines in an
optnone function, but alwaysinline callees should be inlined regardless
of optnone.

Fixes inline-optnone.ll under NPM.

[aeubanks]

Remove unused import

[kazu]

LGTM. Thanks!

[aeubanks]

Actually, I'm wondering if the NPM inliner properly handles alwaysinline in all cases? I don't see any other references to "alwaysinline" in Inliner.cpp (besides some legacy passes).

[aeubanks]

In D83021#2128775, @aeubanks wrote:

Actually, I'm wondering if the NPM inliner properly handles alwaysinline in all cases? I don't see any other references to "alwaysinline" in Inliner.cpp (besides some legacy passes).

jyknight pointed me to llvm::getAttributeBasedInliningDecision() where alwaysinline is handled.
It still seems a little weird to me that alwaysinline isn't a separate pass under the -O1/-O2/-O3 pipelines and would make opt-bisect always run the inliner pass (once it's implemented in NPM). But this will do for now.

llvm/lib/Transforms/IPO/Inliner.cpp

for (int I = 0; I < (int)Calls.size(); ++I) {
     // We expect the calls to typically be batched with sequences of calls that
     // have the same caller, so we first set up some shared infrastructure for
     // this caller. We also do any pruning we can at this layer on the caller
     // alone.
     Function &F = *Calls[I].first->getCaller();
     LazyCallGraph::Node &N = *CG.lookup(F);
     if (CG.lookupSCC(N) != C)
       continue;
-    if (F.hasOptNone()) {
+    if (!Calls[I].first->getCalledFunction()->hasFnAttribute(
+            Attribute::AlwaysInline) &&
+        F.hasOptNone()) {
       setInlineRemark(*Calls[I].first, "optnone attribute");
       continue;
     }
 
     LLVM_DEBUG(dbgs() << "Inlining calls in: " << F.getName() << "\n");
 
     auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & {
       return FAM.getResult<AssumptionAnalysis>(F);

llvm/test/Transforms/Inline/inline-optnone.ll

 ; RUN: opt < %s -inline -S | FileCheck %s
+; RUN: opt < %s --passes=inline -S | FileCheck %s
 
 ; Test that functions with attribute optnone are not inlined.
 ; Also test that only functions with attribute alwaysinline are
 ; valid candidates for inlining if the caller has the optnone attribute.
 
 ; Function Attrs: alwaysinline nounwind readnone uwtable
 define i32 @alwaysInlineFunction(i32 %a) #0 {
 entry: