[Legalizer] Only allocate the SetVectors once per function.

Prior to this patch we used to create SetVectors in temporaries that
were created and destroyed for each instruction. Now, instead we create
and destroyed them only once, but clear the content for each
instruction.
This speeds up the pass by ~25%.

NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315756 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/GlobalISel/Legalizer.cpp b/lib/CodeGen/GlobalISel/Legalizer.cpp
index 1c474b9984601d1071843df3182a4d280f5a262c..a9847dea3cee5c743f8a5420f62f45b6f6cfc661 100644 (file)
--- a/lib/CodeGen/GlobalISel/Legalizer.cpp
+++ b/lib/CodeGen/GlobalISel/Legalizer.cpp
@@ -70,6 +70,9 @@ bool Legalizer::runOnMachineFunction(MachineFunction &MF) {
   // convergence for performance reasons.
   bool Changed = false;
   MachineBasicBlock::iterator NextMI;
+  using VecType = SetVector<MachineInstr *, SmallVector<MachineInstr *, 8>>;
+  VecType WorkList;
+  VecType CombineList;
   for (auto &MBB : MF) {
     for (auto MI = MBB.begin(); MI != MBB.end(); MI = NextMI) {
       // Get the next Instruction before we try to legalize, because there's a
@@ -81,9 +84,8 @@ bool Legalizer::runOnMachineFunction(MachineFunction &MF) {
       if (!isPreISelGenericOpcode(MI->getOpcode()))
         continue;
       unsigned NumNewInsns = 0;
-      using VecType = SetVector<MachineInstr *, SmallVector<MachineInstr *, 8>>;
-      VecType WorkList;
-      VecType CombineList;
+      WorkList.clear();
+      CombineList.clear();
       Helper.MIRBuilder.recordInsertions([&](MachineInstr *MI) {
         // Only legalize pre-isel generic instructions.
         // Legalization process could generate Target specific pseudo