[RISCV] Enable MachineOutliner by default under -Oz for RISCV

Enable default outlining when the function has the minsize attribute.

`addr-label.ll` crashed after enabling this, so a barrier is added before
instruction selection as a workaround.

Reviewed By: luismarques

Differential Revision: https://reviews.llvm.org/D122213

llvm/lib/Target/RISCV/CMakeLists.txt

@@ -47,6 +47,7 @@ add_llvm_target(RISCVCodeGen
   Analysis
   AsmPrinter
   Core
+  IPO
   CodeGen
   MC
   RISCVDesc

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -1196,6 +1196,11 @@ enum MachineOutlinerConstructionID {
   MachineOutlinerDefault
 };
 
+bool RISCVInstrInfo::shouldOutlineFromFunctionByDefault(
+    MachineFunction &MF) const {
+  return MF.getFunction().hasMinSize();
+}
+
 outliner::OutlinedFunction RISCVInstrInfo::getOutliningCandidateInfo(
     std::vector<outliner::Candidate> &RepeatedSequenceLocs) const {
 

llvm/lib/Target/RISCV/RISCVInstrInfo.h

@@ -135,6 +135,8 @@ public:
   virtual bool isMBBSafeToOutlineFrom(MachineBasicBlock &MBB,
                                       unsigned &Flags) const override;
 
+  bool shouldOutlineFromFunctionByDefault(MachineFunction &MF) const override;
+
   // Calculate target-specific information for a set of outlining candidates.
   outliner::OutlinedFunction getOutliningCandidateInfo(
       std::vector<outliner::Candidate> &RepeatedSequenceLocs) const override;

llvm/lib/Target/RISCV/RISCVTargetMachine.cpp

@@ -33,6 +33,7 @@
 #include "llvm/MC/TargetRegistry.h"
 #include "llvm/Support/FormattedStream.h"
 #include "llvm/Target/TargetOptions.h"
+#include "llvm/Transforms/IPO.h"
 using namespace llvm;
 
 static cl::opt<bool> EnableRedundantCopyElimination(
@@ -80,6 +81,7 @@ RISCVTargetMachine::RISCVTargetMachine(const Target &T, const Triple &TT,
 
   // RISC-V supports the MachineOutliner.
   setMachineOutliner(true);
+  setSupportsDefaultOutlining(true);
 }
 
 const RISCVSubtarget *
@@ -141,6 +143,7 @@ public:
   }
 
   void addIRPasses() override;
+  bool addPreISel() override;
   bool addInstSelector() override;
   bool addIRTranslator() override;
   bool addLegalizeMachineIR() override;
@@ -167,6 +170,16 @@ void RISCVPassConfig::addIRPasses() {
   TargetPassConfig::addIRPasses();
 }
 
+bool RISCVPassConfig::addPreISel() {
+  if (TM->getOptLevel() != CodeGenOpt::None) {
+    // Add a barrier before instruction selection so that we will not get
+    // deleted block address after enabling default outlining. See D99707 for
+    // more details.
+    addPass(createBarrierNoopPass());
+  }
+  return false;
+}
+
 bool RISCVPassConfig::addInstSelector() {
   addPass(createRISCVISelDag(getRISCVTargetMachine()));
 

llvm/test/CodeGen/RISCV/O3-pipeline.ll

@@ -60,9 +60,12 @@
 ; CHECK-NEXT:       CodeGen Prepare
 ; CHECK-NEXT:       Dominator Tree Construction
 ; CHECK-NEXT:       Exception handling preparation
+; CHECK-NEXT:     A No-Op Barrier Pass
+; CHECK-NEXT:     FunctionPass Manager
 ; CHECK-NEXT:       Safe Stack instrumentation pass
 ; CHECK-NEXT:       Insert stack protectors
 ; CHECK-NEXT:       Module Verifier
+; CHECK-NEXT:       Dominator Tree Construction
 ; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:       Function Alias Analysis Results
 ; CHECK-NEXT:       Natural Loop Information
@@ -151,6 +154,8 @@
 ; CHECK-NEXT:       Contiguously Lay Out Funclets
 ; CHECK-NEXT:       StackMap Liveness Analysis
 ; CHECK-NEXT:       Live DEBUG_VALUE analysis
+; CHECK-NEXT:     Machine Outliner
+; CHECK-NEXT:     FunctionPass Manager
 ; CHECK-NEXT:       RISCV pseudo instruction expansion pass
 ; CHECK-NEXT:       RISCV atomic pseudo instruction expansion pass
 ; CHECK-NEXT:       Lazy Machine Block Frequency Analysis