Enable MachineOutliner by default under -Oz for AArch64

This patch enables the MachineOutliner by default in AArch64 under -Oz.

The MachineOutliner offers around a 4.5% improvement on the current -Oz code
size improvements.

We have done work into improving the debuggability of outlined code, so that
users of -Oz won't be surprised by the optimization. We have also been executing
the LLVM test suite and common external tests such as the SPEC suites
continuously with no issue. The outliner has a low compile-time overhead of
roughly 1%. At this point, the outliner would be a really good addition to the
-Oz pass pipeline!

llvm-svn: 338133

3 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
index dc3fa4f8c1d..9e5c0b83a4a 100644
--- a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
@@ -5478,3 +5478,8 @@ MachineBasicBlock::iterator AArch64InstrInfo::insertOutlinedCall(
 
   return CallPt;
 }
+
+bool AArch64InstrInfo::shouldOutlineFromFunctionByDefault(
+  MachineFunction &MF) const {
+  return MF.getFunction().optForMinSize();
+}
diff --git a/llvm/lib/Target/AArch64/AArch64InstrInfo.h b/llvm/lib/Target/AArch64/AArch64InstrInfo.h
index 0e5953f6216..585cbd4b9c7 100644
--- a/llvm/lib/Target/AArch64/AArch64InstrInfo.h
+++ b/llvm/lib/Target/AArch64/AArch64InstrInfo.h
@@ -249,6 +249,7 @@ public:
   insertOutlinedCall(Module &M, MachineBasicBlock &MBB,
                      MachineBasicBlock::iterator &It, MachineFunction &MF,
                      const outliner::Candidate &C) const override;
+  bool shouldOutlineFromFunctionByDefault(MachineFunction &MF) const override;
   /// Returns true if the instruction sets to an immediate value that can be
   /// executed more efficiently.
   bool isExynosResetFast(const MachineInstr &MI) const;
diff --git a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
index 01a997e5aed..120d71381c6 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
@@ -255,6 +255,9 @@ AArch64TargetMachine::AArch64TargetMachine(const Target &T, const Triple &TT,
 
   // AArch64 supports the MachineOutliner.
   setMachineOutliner(true);
+
+  // AArch64 supports default outlining behaviour.
+  setSupportsDefaultOutlining(true);
 }
 
 AArch64TargetMachine::~AArch64TargetMachine() = default;