[ShrinkWrap] Add optimization remarks to the shrink-wrapping pass

Start by emitting remarks for very basic unsupported cases such as
irreducible CFGs and EHFunclets. The end goal is to be able to cover all
the cases where we give up with an explanation.

llvm-svn: 333972

1 files changed, 27 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/ShrinkWrap.cpp b/llvm/lib/CodeGen/ShrinkWrap.cpp
index 7647df0d340..d3454ca6ba6 100644
--- a/llvm/lib/CodeGen/ShrinkWrap.cpp
+++ b/llvm/lib/CodeGen/ShrinkWrap.cpp
@@ -63,6 +63,7 @@
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineLoopInfo.h"
 #include "llvm/CodeGen/MachineOperand.h"
+#include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
 #include "llvm/CodeGen/MachinePostDominators.h"
 #include "llvm/CodeGen/RegisterClassInfo.h"
 #include "llvm/CodeGen/RegisterScavenging.h"
@@ -130,6 +131,9 @@ class ShrinkWrap : public MachineFunctionPass {
   /// are in the same loop.
   MachineLoopInfo *MLI;
 
+  // Emit remarks.
+  MachineOptimizationRemarkEmitter *ORE = nullptr;
+
   /// Frequency of the Entry block.
   uint64_t EntryFreq;
 
@@ -189,6 +193,7 @@ class ShrinkWrap : public MachineFunctionPass {
     Restore = nullptr;
     MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
     MLI = &getAnalysis<MachineLoopInfo>();
+    ORE = &getAnalysis<MachineOptimizationRemarkEmitterPass>().getORE();
     EntryFreq = MBFI->getEntryFreq();
     const TargetSubtargetInfo &Subtarget = MF.getSubtarget();
     const TargetInstrInfo &TII = *Subtarget.getInstrInfo();
@@ -222,6 +227,7 @@ public:
     AU.addRequired<MachineDominatorTree>();
     AU.addRequired<MachinePostDominatorTree>();
     AU.addRequired<MachineLoopInfo>();
+    AU.addRequired<MachineOptimizationRemarkEmitterPass>();
     MachineFunctionPass::getAnalysisUsage(AU);
   }
 
@@ -248,6 +254,7 @@ INITIALIZE_PASS_DEPENDENCY(MachineBlockFrequencyInfo)
 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
 INITIALIZE_PASS_DEPENDENCY(MachinePostDominatorTree)
 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
+INITIALIZE_PASS_DEPENDENCY(MachineOptimizationRemarkEmitterPass)
 INITIALIZE_PASS_END(ShrinkWrap, DEBUG_TYPE, "Shrink Wrap Pass", false, false)
 
 bool ShrinkWrap::useOrDefCSROrFI(const MachineInstr &MI,
@@ -432,6 +439,19 @@ void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB,
   }
 }
 
+static bool giveUpWithRemarks(MachineOptimizationRemarkEmitter *ORE,
+                              StringRef RemarkName, StringRef RemarkMessage,
+                              const DiagnosticLocation &Loc,
+                              const MachineBasicBlock *MBB) {
+  ORE->emit([&]() {
+    return MachineOptimizationRemarkMissed(DEBUG_TYPE, RemarkName, Loc, MBB)
+           << RemarkMessage;
+  });
+
+  LLVM_DEBUG(dbgs() << RemarkMessage << '\n');
+  return false;
+}
+
 bool ShrinkWrap::runOnMachineFunction(MachineFunction &MF) {
   if (skipFunction(MF.getFunction()) || MF.empty() || !isShrinkWrapEnabled(MF))
     return false;
@@ -448,8 +468,9 @@ bool ShrinkWrap::runOnMachineFunction(MachineFunction &MF) {
     // results. Moreover, we may miss that the prologue and
     // epilogue are not in the same loop, leading to unbalanced
     // construction/deconstruction of the stack frame.
-    LLVM_DEBUG(dbgs() << "Irreducible CFGs are not supported yet\n");
-    return false;
+    return giveUpWithRemarks(ORE, "UnsupportedIrreducibleCFG",
+                             "Irreducible CFGs are not supported yet.",
+                             MF.getFunction().getSubprogram(), &MF.front());
   }
 
   const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
@@ -460,10 +481,10 @@ bool ShrinkWrap::runOnMachineFunction(MachineFunction &MF) {
     LLVM_DEBUG(dbgs() << "Look into: " << MBB.getNumber() << ' '
                       << MBB.getName() << '\n');
 
-    if (MBB.isEHFuncletEntry()) {
-      LLVM_DEBUG(dbgs() << "EH Funclets are not supported yet.\n");
-      return false;
-    }
+    if (MBB.isEHFuncletEntry())
+      return giveUpWithRemarks(ORE, "UnsupportedEHFunclets",
+                               "EH Funclets are not supported yet.",
+                               MBB.front().getDebugLoc(), &MBB);
 
     if (MBB.isEHPad()) {
       // Push the prologue and epilogue outside of