MachineSink: Collect registers before clearing their killflags.

Currently whenever we sink any instruction, we do clearKillFlags for
every use of every use operand for that instruction, apparently there
are a lot of duplication, therefore compile time penalties.

This patch collect all the interested registers first, do clearKillFlags
for it all together at once at the end, so we only need to do
clearKillFlags once for one register, duplication is avoided.

Patch by Lawrence Hu!

Differential Revision: http://reviews.llvm.org/D9719

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237510 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MachineSink.cpp

@@ -19,6 +19,7 @@
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/SparseBitVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
@@ -70,6 +71,8 @@ namespace {
     // will be split.
     SetVector<std::pair<MachineBasicBlock*,MachineBasicBlock*> > ToSplit;
 
+    SparseBitVector<> RegsToClearKillFlags;
+
   public:
     static char ID; // Pass identification
     MachineSinking() : MachineFunctionPass(ID) {
@@ -287,6 +290,12 @@ bool MachineSinking::runOnMachineFunction(MachineFunction &MF) {
     if (!MadeChange) break;
     EverMadeChange = true;
   }
+
+  // Now clear any kill flags for recorded registers.
+  for (auto I : RegsToClearKillFlags)
+    MRI->clearKillFlags(I);
+  RegsToClearKillFlags.clear();
+
   return EverMadeChange;
 }
 
@@ -761,7 +770,7 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
   // used registers.
   for (MachineOperand &MO : MI->operands()) {
     if (MO.isReg() && MO.isUse())
-      MRI->clearKillFlags(MO.getReg());
+      RegsToClearKillFlags.set(MO.getReg()); // Remember to clear kill flags.
   }
 
   return true;