Move the FindCopyInsertPoint method of PHIElimination to a new standalone

function so that it can be shared with StrongPHIElimination.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120951 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 61 insertions, 0 deletions

diff --git a/lib/CodeGen/PHIEliminationUtils.cpp b/lib/CodeGen/PHIEliminationUtils.cpp
new file mode 100644
index 0000000000..10bfdcce67
--- /dev/null
+++ b/lib/CodeGen/PHIEliminationUtils.cpp
@@ -0,0 +1,61 @@
+//===-- PHIEliminationUtils.cpp - Helper functions for PHI elimination ----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "PHIEliminationUtils.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/ADT/SmallPtrSet.h"
+using namespace llvm;
+
+// findCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg
+// when following the CFG edge to SuccMBB. This needs to be after any def of
+// SrcReg, but before any subsequent point where control flow might jump out of
+// the basic block.
+MachineBasicBlock::iterator
+llvm::findPHICopyInsertPoint(MachineBasicBlock* MBB, MachineBasicBlock* SuccMBB,
+                             unsigned SrcReg) {
+  // Handle the trivial case trivially.
+  if (MBB->empty())
+    return MBB->begin();
+
+  // Usually, we just want to insert the copy before the first terminator
+  // instruction. However, for the edge going to a landing pad, we must insert
+  // the copy before the call/invoke instruction.
+  if (!SuccMBB->isLandingPad())
+    return MBB->getFirstTerminator();
+
+  // Discover any defs/uses in this basic block.
+  SmallPtrSet<MachineInstr*, 8> DefUsesInMBB;
+  MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo();
+  for (MachineRegisterInfo::reg_iterator RI = MRI.reg_begin(SrcReg),
+         RE = MRI.reg_end(); RI != RE; ++RI) {
+    MachineInstr* DefUseMI = &*RI;
+    if (DefUseMI->getParent() == MBB)
+      DefUsesInMBB.insert(DefUseMI);
+  }
+
+  MachineBasicBlock::iterator InsertPoint;
+  if (DefUsesInMBB.empty()) {
+    // No defs.  Insert the copy at the start of the basic block.
+    InsertPoint = MBB->begin();
+  } else if (DefUsesInMBB.size() == 1) {
+    // Insert the copy immediately after the def/use.
+    InsertPoint = *DefUsesInMBB.begin();
+    ++InsertPoint;
+  } else {
+    // Insert the copy immediately after the last def/use.
+    InsertPoint = MBB->end();
+    while (!DefUsesInMBB.count(&*--InsertPoint)) {}
+    ++InsertPoint;
+  }
+
+  // Make sure the copy goes after any phi nodes however.
+  return MBB->SkipPHIsAndLabels(InsertPoint);
+}