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, 5 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/LiveInterval.cpp b/llvm/lib/CodeGen/LiveInterval.cpp
index 97926dd6fd5..4d3ce3a9d43 100644
--- a/llvm/lib/CodeGen/LiveInterval.cpp
+++ b/llvm/lib/CodeGen/LiveInterval.cpp
@@ -507,12 +507,11 @@ void LiveInterval::join(LiveInterval &Other, const int *LHSValNoAssignments,
   // Update regalloc hint if currently there isn't one.
   if (TargetRegisterInfo::isVirtualRegister(reg) &&
       TargetRegisterInfo::isVirtualRegister(Other.reg)) {
-    std::pair<MachineRegisterInfo::RegAllocHintType, unsigned> Hint =
-      MRI->getRegAllocationHint(reg);
-    if (Hint.first == MachineRegisterInfo::RA_None) {
-      std::pair<MachineRegisterInfo::RegAllocHintType, unsigned> OtherHint =
+    std::pair<unsigned, unsigned> Hint = MRI->getRegAllocationHint(reg);
+    if (Hint.first == 0 && Hint.second == 0) {
+      std::pair<unsigned, unsigned> OtherHint =
         MRI->getRegAllocationHint(Other.reg);
-      if (OtherHint.first != MachineRegisterInfo::RA_None)
+      if (OtherHint.first || OtherHint.second)
         MRI->setRegAllocationHint(reg, OtherHint.first, OtherHint.second);
     }
   }
@@ -772,8 +771,7 @@ void LiveInterval::Copy(const LiveInterval &RHS,
                         BumpPtrAllocator &VNInfoAllocator) {
   ranges.clear();
   valnos.clear();
-  std::pair<MachineRegisterInfo::RegAllocHintType, unsigned> Hint =
-    MRI->getRegAllocationHint(RHS.reg);
+  std::pair<unsigned, unsigned> Hint = MRI->getRegAllocationHint(RHS.reg);
   MRI->setRegAllocationHint(reg, Hint.first, Hint.second);
 
   weight = RHS.weight;