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, 1 deletions

diff --git a/llvm/lib/CodeGen/RegAllocBasic.cpp b/llvm/lib/CodeGen/RegAllocBasic.cpp
index 18d6f47..d1b289b 100644
--- a/llvm/lib/CodeGen/RegAllocBasic.cpp
+++ b/llvm/lib/CodeGen/RegAllocBasic.cpp
@@ -342,7 +342,10 @@ bool RABasic::runOnMachineFunction(MachineFunction &mf) {
   // Write out new DBG_VALUE instructions.
   getAnalysis<LiveDebugVariables>().emitDebugValues(VRM);
 
-  // The pass output is in VirtRegMap. Release all the transient data.
+  // All machine operands and other references to virtual registers have been
+  // replaced. Remove the virtual registers and release all the transient data.
+  VRM->clearAllVirt();
+  MRI->clearVirtRegs();
   releaseMemory();
 
   return true;