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

This is a recommit of r335887, which was erroneously committed earlier.

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.

https://reviews.llvm.org/D48682

llvm-svn: 335986

llvm/lib/CodeGen/TargetPassConfig.cpp

@@ -111,9 +111,16 @@ 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.
@@ -907,7 +914,7 @@ void TargetPassConfig::addMachinePasses() {
   addPass(&PatchableFunctionID, false);
 
   if (TM->Options.EnableMachineOutliner && getOptLevel() != CodeGenOpt::None &&
-      EnableMachineOutliner)
+      EnableMachineOutliner == AlwaysOutline)
     addPass(createMachineOutlinerPass());
 
   // Add passes that directly emit MI after all other MI passes.

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

@@ -1,7 +1,15 @@
+; 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
@@ -15,12 +23,16 @@
 ;
 ; Cases where it should be added:
 ;  * -enable-machine-outliner
+;  * -enable-machine-outliner=always
 ;
 ; Cases where it should not be added:
 ;  * -O0 or equivalent
 ;  * -enable-machine-outliner is not passed
+;  * -enable-machine-outliner=never is passed
 
+; ALWAYS: Machine Outliner
 ; ENABLE: Machine Outliner
+; NEVER-NOT: Machine Outliner
 ; NOT-ADDED-NOT: Machine Outliner
 ; OPTNONE-NOT: Machine Outliner