Update PEI's virtual-register-based scavenging to support multiple simultaneous mappings

The previous algorithm could not deal properly with scavenging multiple virtual
registers because it kept only one live virtual -> physical mapping (and
iterated through operands in order). Now we don't maintain a current mapping,
but rather use replaceRegWith to completely remove the virtual register as
soon as the mapping is established.

In order to allow the register scavenger to return a physical register killed
by an instruction for definition by that same instruction, we now call
RS->forward(I) prior to eliminating virtual registers defined in I. This
requires a minor update to forward to ignore virtual registers.

These new features will be tested in forthcoming commits.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178058 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 2 deletions

diff --git a/include/llvm/CodeGen/RegisterScavenging.h b/include/llvm/CodeGen/RegisterScavenging.h
index babb96b962..0eb2b2ab07 100644
--- a/include/llvm/CodeGen/RegisterScavenging.h
+++ b/include/llvm/CodeGen/RegisterScavenging.h
@@ -94,8 +94,11 @@ public:
   }
 
   /// skipTo - Move the internal MBB iterator but do not update register states.
-  ///
-  void skipTo(MachineBasicBlock::iterator I) { MBBI = I; }
+  void skipTo(MachineBasicBlock::iterator I) {
+    if (I == MachineBasicBlock::iterator(NULL))
+      Tracking = false;
+    MBBI = I;
+  }
 
   /// getRegsUsed - return all registers currently in use in used.
   void getRegsUsed(BitVector &used, bool includeReserved);