[MachineOutliner] Add always and never options to -enable-machine-outliner

[paquette]

Summary

To enable the MachineOutliner by default on AArch64, we need to be able to disable the MachineOutliner and also provide an option to "always" enable the outliner.

This adds that capability. It allows the user to still use the old -enable-machine-outliner option, which defaults to "always". This is building up to allowing the user to specify "always" versus the target default outlining behaviour.

[javed.absar]

lib/CodeGen/TargetPassConfig.cpp

121

"linkonceodr" - is it a typo? not sure how to read this

[paquette]

lib/CodeGen/TargetPassConfig.cpp

121

The intention was to say "I would also like to outline from functions with linkonceodr linkage", which the outliner doesn't do by default. I'm open to changing this if it's confusing though. Any thoughts?

[paquette]

lib/CodeGen/TargetPassConfig.cpp

121

Actually, I see why this is confusing. I'll just remove the note since it's kind of misleading.

[paquette]

Removed the reference to enable-linkonceodr-outlining, since it was confusing.

[javed.absar]

Thanks. LGTM.

[paquette]

Thanks!

Committed in r335986.
https://reviews.llvm.org/rL335986

lib/CodeGen/TargetPassConfig.cpp

 static cl::opt<bool> PrintISelInput("print-isel-input", cl::Hidden,
     cl::desc("Print LLVM IR input to isel pass"));
 static cl::opt<bool> PrintGCInfo("print-gc", cl::Hidden,
     cl::desc("Dump garbage collector data"));
 static cl::opt<bool> VerifyMachineCode("verify-machineinstrs", cl::Hidden,
     cl::desc("Verify generated machine code"),
     cl::init(false),
     cl::ZeroOrMore);
-static cl::opt<bool> EnableMachineOutliner("enable-machine-outliner",
-    cl::Hidden,
-    cl::desc("Enable machine outliner"));
+enum RunOutliner { AlwaysOutline, NeverOutline };
+// Enable or disable the MachineOutliner.
+static cl::opt<RunOutliner> EnableMachineOutliner(
+    "enable-machine-outliner", cl::desc("Enable the machine outliner"),
+    cl::Hidden, cl::ValueOptional, cl::init(NeverOutline),
+    cl::values(clEnumValN(AlwaysOutline, "always",
+                          "Run on all functions guaranteed to be beneficial"),
+               clEnumValN(NeverOutline, "never", "Disable all outlining"),
+               // Sentinel value for unspecified option.
+               clEnumValN(AlwaysOutline, "", "")));
 // Enable or disable FastISel. Both options are needed, because
 // FastISel is enabled by default with -fast, and we wish to be
 // able to enable or disable fast-isel independently from -O0.
 static cl::opt<cl::boolOrDefault>
 EnableFastISelOption("fast-isel", cl::Hidden,
   cl::desc("Enable the \"fast\" instruction selector"));
 
 static cl::opt<cl::boolOrDefault> EnableGlobalISelOption(
void TargetPassConfig::addMachinePasses() {
 
   // Insert before XRay Instrumentation.
   addPass(&FEntryInserterID, false);
 
   addPass(&XRayInstrumentationID, false);
   addPass(&PatchableFunctionID, false);
 
   if (TM->Options.EnableMachineOutliner &&
-      EnableMachineOutliner)
+      EnableMachineOutliner == AlwaysOutline)
     addPass(createMachineOutlinerPass());
 
   // Add passes that directly emit MI after all other MI passes.
   addPreEmitPass2();
 
   AddingMachinePasses = false;
 }
 

test/CodeGen/AArch64/machine-outliner-flags.ll

+; RUN: llc %s -debug-pass=Structure -verify-machineinstrs \
+; RUN: -enable-machine-outliner=always -mtriple arm64---- -o /dev/null 2>&1 \
+; RUN: | FileCheck %s -check-prefix=ALWAYS
+
+; RUN: llc %s -debug-pass=Structure -verify-machineinstrs \
+; RUN: -enable-machine-outliner -mtriple arm64---- -o /dev/null 2>&1 \
+; RUN: | FileCheck %s -check-prefix=ENABLE
+
+; RUN: llc %s -debug-pass=Structure -verify-machineinstrs \
+; RUN: -enable-machine-outliner=never -mtriple arm64---- -o /dev/null 2>&1 \
+; RUN: | FileCheck %s -check-prefix=NEVER
+
+; RUN: llc %s -debug-pass=Structure -verify-machineinstrs \
+; RUN: -mtriple arm64---- -o /dev/null 2>&1 \
+; RUN: | FileCheck %s -check-prefix=NOT-ADDED
+
+; Make sure that the outliner flags all work properly. If we specify
+; -enable-machine-outliner with always or no argument, it should be added to the
+; pass pipeline. If we specify it with never, or don't pass the flag,
+; then we shouldn't add it.
+
+; ALWAYS: Machine Outliner
+; ENABLE: Machine Outliner
+; NEVER-NOT: Machine Outliner
+; NOT-ADDED-NOT: Machine Outliner
+
+define void @foo() {
+  ret void;
+}
+