[MachineCopyPropagation] Expose more dead copies across instructions with regmasks

When encountering instructions with regmasks, instead of cleaning up all the
elements in MaybeDeadCopies map, remove only the instructions erased. By keeping
more instruction in MaybeDeadCopies, this change will expose more dead copies
across instructions with regmasks.

llvm-svn: 264462

1 files changed, 14 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/MachineCopyPropagation.cpp b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
index 2bfd65019fc..3a6f2b5330e 100644
--- a/llvm/lib/CodeGen/MachineCopyPropagation.cpp
+++ b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
@@ -285,18 +285,28 @@ void MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
     // defined registers.
     if (RegMask) {
       // Erase any MaybeDeadCopies whose destination register is clobbered.
-      for (MachineInstr *MaybeDead : MaybeDeadCopies) {
+      for (SmallSetVector<MachineInstr *, 8>::iterator DI =
+               MaybeDeadCopies.begin();
+           DI != MaybeDeadCopies.end();) {
+        MachineInstr *MaybeDead = *DI;
         unsigned Reg = MaybeDead->getOperand(0).getReg();
         assert(!MRI->isReserved(Reg));
-        if (!RegMask->clobbersPhysReg(Reg))
+
+        if (!RegMask->clobbersPhysReg(Reg)) {
+          ++DI;
           continue;
+        }
+
         DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
               MaybeDead->dump());
+
+        // erase() will return the next valid iterator pointing to the next
+        // element after the erased one.
+        DI = MaybeDeadCopies.erase(DI);
         MaybeDead->eraseFromParent();
         Changed = true;
         ++NumDeletes;
       }
-      MaybeDeadCopies.clear();
 
       removeClobberedRegsFromMap(AvailCopyMap, *RegMask);
       removeClobberedRegsFromMap(CopyMap, *RegMask);
@@ -348,3 +358,4 @@ bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) {
 
   return Changed;
 }
+