[IR/MachineOutliner] Add a "nooutline" function attr and respect it

Add `nooutline` + update LangRef to say it exists.

This makes it possible to say "don't outline from this function ever."

We want to be able to toggle whether or not a function should be in the search
set regardless of default behaviour.

Add testcases for the IR Outliner + Machine Outliner.

Also remove an unnecessary check for an empty function in the Machine Outliner.

Differential Revision: https://reviews.llvm.org/D140438

1 files changed, 6 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/MachineOutliner.cpp b/llvm/lib/CodeGen/MachineOutliner.cpp
index 56c3d27..c7ba66b 100644
--- a/llvm/lib/CodeGen/MachineOutliner.cpp
+++ b/llvm/lib/CodeGen/MachineOutliner.cpp
@@ -880,10 +880,13 @@ void MachineOutliner::populateMapper(InstructionMapper &Mapper, Module &M,
   // iterating over each Function in M.
   for (Function &F : M) {
 
-    // If there's nothing in F, then there's no reason to try and outline from
-    // it.
-    if (F.empty())
+    if (F.hasFnAttribute("nooutline")) {
+      LLVM_DEBUG({
+        dbgs() << "... Skipping function with nooutline attribute: "
+               << F.getName() << "\n";
+      });
       continue;
+    }
 
     // There's something in F. Check if it has a MachineFunction associated with
     // it.