Clear virtual registers after they are no longer referenced.

Passes after RegAlloc should be able to rely on MRI->getNumVirtRegs() == 0.
This makes sharing code for pre/postRA passes more robust.
Now, to check if a pass is running before the RA pipeline begins, use MRI->isSSA().
To check if a pass is running after the RA pipeline ends, use !MRI->getNumVirtRegs().

PEI resets virtual regs when it's done scavenging.

PTX will either have to provide its own PEI pass or assign physregs.

llvm-svn: 151032

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/RegAllocFast.cpp b/llvm/lib/CodeGen/RegAllocFast.cpp
index 6d7b5f4b656..b8b05a9f60d 100644
--- a/llvm/lib/CodeGen/RegAllocFast.cpp
+++ b/llvm/lib/CodeGen/RegAllocFast.cpp
@@ -1104,6 +1104,10 @@ bool RAFast::runOnMachineFunction(MachineFunction &Fn) {
       while (*Defs)
         MRI->setPhysRegUsed(*Defs++);
 
+  // All machine operands and other references to virtual registers have been
+  // replaced. Remove the virtual registers.
+  MRI->clearVirtRegs();
+
   SkippedInstrs.clear();
   StackSlotForVirtReg.clear();
   LiveDbgValueMap.clear();