Teach the register scavenger to take subregs into account when finding a free register.

llvm-svn: 127049

1 files changed, 10 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/RegisterScavenging.cpp b/llvm/lib/CodeGen/RegisterScavenging.cpp
index a2580b85bcc..b9dd28e5c78 100644
--- a/llvm/lib/CodeGen/RegisterScavenging.cpp
+++ b/llvm/lib/CodeGen/RegisterScavenging.cpp
@@ -241,12 +241,13 @@ unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RC) const {
 
 /// getRegsAvailable - Return all available registers in the register class
 /// in Mask.
-void RegScavenger::getRegsAvailable(const TargetRegisterClass *RC,
-                                    BitVector &Mask) {
+BitVector RegScavenger::getRegsAvailable(const TargetRegisterClass *RC) {
+  BitVector Mask(TRI->getNumRegs());
   for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end();
        I != E; ++I)
     if (!isAliasUsed(*I))
       Mask.set(*I);
+  return Mask;
 }
 
 /// findSurvivorReg - Return the candidate register that is unused for the
@@ -335,9 +336,13 @@ unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC,
   }
 
   // Try to find a register that's unused if there is one, as then we won't
-  // have to spill.
-  if ((Candidates & RegsAvailable).any())
-     Candidates &= RegsAvailable;
+  // have to spill. Search explicitly rather than masking out based on
+  // RegsAvailable, as RegsAvailable does not take aliases into account.
+  // That's what getRegsAvailable() is for.
+  BitVector Available = getRegsAvailable(RC);
+
+  if ((Candidates & Available).any())
+     Candidates &= Available;
 
   // Find the register whose use is furthest away.
   MachineBasicBlock::iterator UseMI;