[clang][NewPM] Do not eliminate available_externally durng `-O2 -flto` runs

[leonardchan]

Summary

This fixes CodeGen/available-externally-suppress.c when the new pass manager is turned on by default. available_externally was not emitted during -O2 -flto runs when it should still be retained for link time inlining purposes. This can be fixed by checking that we aren't LTOPrelinking when adding the EliminateAvailableExternallyPass.

[chandlerc]

LGTM, again, really nice. Tiny tweak below.

llvm/test/Other/available-externally-lto.ll

2

Wrap to 80-columns?

clang/test/CodeGen/available-externally-suppress.c

-// RUN: %clang_cc1 -emit-llvm -o - -triple x86_64-apple-darwin10 %s | FileCheck %s
-// RUN: %clang_cc1 -O2 -fno-inline -emit-llvm -o - -triple x86_64-apple-darwin10 %s | FileCheck %s
-// RUN: %clang_cc1 -flto -O2 -fno-inline -emit-llvm -o - -triple x86_64-apple-darwin10 %s | FileCheck %s -check-prefix=LTO
+// RUN: %clang_cc1 -fno-experimental-new-pass-manager -emit-llvm -o - -triple x86_64-apple-darwin10 %s | FileCheck %s
+// RUN: %clang_cc1 -fno-experimental-new-pass-manager -O2 -fno-inline -emit-llvm -o - -triple x86_64-apple-darwin10 %s | FileCheck %s
+// RUN: %clang_cc1 -fno-experimental-new-pass-manager -flto -O2 -fno-inline -emit-llvm -o - -triple x86_64-apple-darwin10 %s | FileCheck %s -check-prefix=LTO
+// RUN: %clang_cc1 -fexperimental-new-pass-manager -emit-llvm -o - -triple x86_64-apple-darwin10 %s | FileCheck %s
+// RUN: %clang_cc1 -fexperimental-new-pass-manager -O2 -fno-inline -emit-llvm -o - -triple x86_64-apple-darwin10 %s | FileCheck %s
+// RUN: %clang_cc1 -fexperimental-new-pass-manager -flto -O2 -fno-inline -emit-llvm -o - -triple x86_64-apple-darwin10 %s | FileCheck %s -check-prefix=LTO
 
 // Ensure that we don't emit available_externally functions at -O0.
 // Also should not emit them at -O2, unless -flto is present in which case
 // we should preserve them for link-time inlining decisions.
 int x;
 
 inline void f0(int y) { x = y; }
 

llvm/lib/Passes/PassBuilder.cpp

ModulePassManager PassBuilder::buildModuleOptimizationPipeline(
 
   // 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
   // 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 globals referenced by available external functions dead and saves
-  // running remaining passes on the eliminated functions.
+  // running remaining passes on the eliminated functions. These should be
+  // preserved during prelinking for link-time inlining decisions.
+  if (!LTOPreLink)
     MPM.addPass(EliminateAvailableExternallyPass());
 
   if (EnableOrderFileInstrumentation)
     MPM.addPass(InstrOrderFilePass());
 
   // Do RPO function attribute inference across the module to forward-propagate
   // attributes where applicable.
   // FIXME: Is this really an optimization rather than a canonicalization?
   MPM.addPass(ReversePostOrderFunctionAttrsPass());

llvm/test/Other/available-externally-lto.ll

+; Ensure that we don't emit available_externally functions at -O2, unless
+; -flto is present in which case we should preserve them for link-time inlining
+; decisions.
+; RUN: opt < %s -S -passes='default<O2>' | FileCheck %s
+; RUN: opt < %s -S -passes='lto-pre-link<O2>' | FileCheck %s --check-prefix=LTO
+
+@x = common local_unnamed_addr global i32 0, align 4
+
+define void @test() local_unnamed_addr #0 {
+entry:
+  tail call void @f0(i32 17)
+  ret void
+}
+
+; CHECK: declare void @f0(i32)
+; LTO: define available_externally void @f0(i32 %y)
+define available_externally void @f0(i32 %y) local_unnamed_addr #0 {
+entry:
+  store i32 %y, i32* @x, align 4
+  ret void
+}
+
+attributes #0 = { noinline }