Add register-reuse to frame-index register scavenging. When a target uses

a virtual register to eliminate a frame index, it can return that register
and the constant stored there to PEI to track. When scavenging to allocate
for those registers, PEI then tracks the last-used register and value, and
if it is still available and matches the value for the next index, reuses
the existing value rather and removes the re-materialization instructions.
Fancier tracking and adjustment of scavenger allocations to keep more
values live for longer is possible, but not yet implemented and would likely
be better done via a different, less special-purpose, approach to the
problem.

eliminateFrameIndex() is modified so the target implementations can return
the registers they wish to be tracked for reuse.

ARM Thumb1 implements and utilizes the new mechanism. All other targets are
simply modified to adjust for the changed eliminateFrameIndex() prototype.

llvm-svn: 83467

1 files changed, 8 insertions, 5 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCRegisterInfo.cpp b/llvm/lib/Target/PowerPC/PPCRegisterInfo.cpp
index f120caaa42d..cf5c7c0f598 100644
--- a/llvm/lib/Target/PowerPC/PPCRegisterInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCRegisterInfo.cpp
@@ -699,8 +699,10 @@ void PPCRegisterInfo::lowerCRSpilling(MachineBasicBlock::iterator II,
   MBB.erase(II);
 }
 
-void PPCRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
-                                          int SPAdj, RegScavenger *RS) const {
+unsigned
+PPCRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
+                                     int SPAdj, int *Value,
+                                     RegScavenger *RS) const {
   assert(SPAdj == 0 && "Unexpected");
 
   // Get the instruction.
@@ -739,14 +741,14 @@ void PPCRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   if (FPSI && FrameIndex == FPSI &&
       (OpC == PPC::DYNALLOC || OpC == PPC::DYNALLOC8)) {
     lowerDynamicAlloc(II, SPAdj, RS);
-    return;
+    return 0;
   }
 
   // Special case for pseudo-op SPILL_CR.
   if (EnableRegisterScavenging) // FIXME (64-bit): Enable by default.
     if (OpC == PPC::SPILL_CR) {
       lowerCRSpilling(II, FrameIndex, SPAdj, RS);
-      return;
+      return 0;
     }
 
   // Replace the FrameIndex with base register with GPR1 (SP) or GPR31 (FP).
@@ -788,7 +790,7 @@ void PPCRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
     if (isIXAddr)
       Offset >>= 2;    // The actual encoded value has the low two bits zero.
     MI.getOperand(OffsetOperandNo).ChangeToImmediate(Offset);
-    return;
+    return 0;
   }
 
   // The offset doesn't fit into a single register, scavenge one to build the
@@ -828,6 +830,7 @@ void PPCRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   unsigned StackReg = MI.getOperand(FIOperandNo).getReg();
   MI.getOperand(OperandBase).ChangeToRegister(StackReg, false);
   MI.getOperand(OperandBase + 1).ChangeToRegister(SReg, false);
+  return 0;
 }
 
 /// VRRegNo - Map from a numbered VR register to its enum value.