Part 1.

- Change register allocation hint to a pair of unsigned integers. The hint type is zero (which means prefer the register specified as second part of the pair) or entirely target dependent.
- Allow targets to specify alternative register allocation orders based on allocation hint.

Part 2.
- Use the register allocation hint system to implement more aggressive load / store multiple formation.
- Aggressively form LDRD / STRD. These are formed *before* register allocation. It has to be done this way to shorten live interval of base and offset registers. e.g.
v1025 = LDR v1024, 0
v1026 = LDR v1024, 0
=>
v1025,v1026 = LDRD v1024, 0

If this transformation isn't done before allocation, v1024 will overlap v1025 which means it more difficult to allocate a register pair.

- Even with the register allocation hint, it may not be possible to get the desired allocation. In that case, the post-allocation load / store multiple pass must fix the ldrd / strd instructions. They can either become ldm / stm instructions or back to a pair of ldr / str instructions.

This is work in progress, not yet enabled.

llvm-svn: 73381

1 files changed, 9 insertions, 30 deletions

diff --git a/llvm/lib/CodeGen/VirtRegMap.cpp b/llvm/lib/CodeGen/VirtRegMap.cpp
index 87d75dd006d..4d3417fdff5 100644
--- a/llvm/lib/CodeGen/VirtRegMap.cpp
+++ b/llvm/lib/CodeGen/VirtRegMap.cpp
@@ -100,36 +100,15 @@ void VirtRegMap::grow() {
 }
 
 unsigned VirtRegMap::getRegAllocPref(unsigned virtReg) {
-  std::pair<MachineRegisterInfo::RegAllocHintType, unsigned> Hint =
-    MRI->getRegAllocationHint(virtReg);
-  switch (Hint.first) {
-  default: assert(0);
-  case MachineRegisterInfo::RA_None:
-    return 0;
-  case MachineRegisterInfo::RA_Preference:
-    if (TargetRegisterInfo::isPhysicalRegister(Hint.second))
-      return Hint.second;
-    if (hasPhys(Hint.second))
-      return getPhys(Hint.second);
-  case MachineRegisterInfo::RA_PairEven: {
-    unsigned physReg = Hint.second;
-    if (TargetRegisterInfo::isPhysicalRegister(physReg))
-      return TRI->getRegisterPairEven(*MF, physReg);
-    else if (hasPhys(physReg))
-      return TRI->getRegisterPairEven(*MF, getPhys(physReg));
-    return 0;
-  }
-  case MachineRegisterInfo::RA_PairOdd: {
-    unsigned physReg = Hint.second;
-    if (TargetRegisterInfo::isPhysicalRegister(physReg))
-      return TRI->getRegisterPairOdd(*MF, physReg);
-    else if (hasPhys(physReg))
-      return TRI->getRegisterPairOdd(*MF, getPhys(physReg));
-    return 0;
-  }
-  }
-  // Shouldn't reach here.
-  return 0;
+  std::pair<unsigned, unsigned> Hint = MRI->getRegAllocationHint(virtReg);
+  unsigned physReg = Hint.second;
+  if (physReg &&
+      TargetRegisterInfo::isVirtualRegister(physReg) && hasPhys(physReg))
+    physReg = getPhys(physReg);
+  if (Hint.first == 0)
+    return (physReg && TargetRegisterInfo::isPhysicalRegister(physReg))
+      ? physReg : 0;
+  return TRI->ResolveRegAllocHint(Hint.first, physReg, *MF);
 }
 
 int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) {