Add CoalescerPair helper class.

Given a copy instruction, CoalescerPair can determine which registers to
coalesce in order to eliminate the copy. It deals with all the subreg fun to
determine a tuple (DstReg, SrcReg, SubIdx) such that:

- SrcReg is a virtual register that will disappear after coalescing.
- DstReg is a virtual or physical register whose live range will be extended.
- SubIdx is 0 when DstReg is a physical register.
- SrcReg can be joined with DstReg:SubIdx.

CoalescerPair::isCoalescable() determines if another copy instruction is
compatible with the same tuple. This fixes some NEON miscompilations where
shuffles are getting coalesced as if they were copies.

The CoalescerPair class will replace a lot of the spaghetti logic in JoinCopy
later.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@105997 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 147 insertions, 0 deletions

diff --git a/lib/CodeGen/RegisterCoalescer.cpp b/lib/CodeGen/RegisterCoalescer.cpp
index 1131e3db4e..b18f0957b6 100644
--- a/lib/CodeGen/RegisterCoalescer.cpp
+++ b/lib/CodeGen/RegisterCoalescer.cpp
@@ -16,6 +16,8 @@
 #include "llvm/CodeGen/RegisterCoalescer.h"
 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
 #include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Pass.h"
 
@@ -33,6 +35,151 @@ char RegisterCoalescer::ID = 0;
 //
 RegisterCoalescer::~RegisterCoalescer() {}
 
+unsigned CoalescerPair::compose(unsigned a, unsigned b) const {
+  if (!a) return b;
+  if (!b) return a;
+  return tri_.composeSubRegIndices(a, b);
+}
+
+bool CoalescerPair::isMoveInstr(const MachineInstr *MI,
+                                unsigned &Src, unsigned &Dst,
+                                unsigned &SrcSub, unsigned &DstSub) const {
+  if (MI->isExtractSubreg()) {
+    Dst = MI->getOperand(0).getReg();
+    DstSub = MI->getOperand(0).getSubReg();
+    Src = MI->getOperand(1).getReg();
+    SrcSub = compose(MI->getOperand(1).getSubReg(), MI->getOperand(2).getImm());
+  } else if (MI->isInsertSubreg() || MI->isSubregToReg()) {
+    Dst = MI->getOperand(0).getReg();
+    DstSub = compose(MI->getOperand(0).getSubReg(), MI->getOperand(3).getImm());
+    Src = MI->getOperand(2).getReg();
+    SrcSub = MI->getOperand(2).getSubReg();
+  } else if (!tii_.isMoveInstr(*MI, Src, Dst, SrcSub, DstSub)) {
+    return false;
+  }
+  return true;
+}
+
+bool CoalescerPair::setRegisters(const MachineInstr *MI) {
+  srcReg_ = dstReg_ = subIdx_ = 0;
+  newRC_ = 0;
+  flipped_ = false;
+
+  unsigned Src, Dst, SrcSub, DstSub;
+  if (!isMoveInstr(MI, Src, Dst, SrcSub, DstSub))
+    return false;
+  partial_ = SrcSub || DstSub;
+
+  // If one register is a physreg, it must be Dst.
+  if (TargetRegisterInfo::isPhysicalRegister(Src)) {
+    if (TargetRegisterInfo::isPhysicalRegister(Dst))
+      return false;
+    std::swap(Src, Dst);
+    std::swap(SrcSub, DstSub);
+    flipped_ = true;
+  }
+
+  const MachineRegisterInfo &MRI = MI->getParent()->getParent()->getRegInfo();
+
+  if (TargetRegisterInfo::isPhysicalRegister(Dst)) {
+    // Eliminate DstSub on a physreg.
+    if (DstSub) {
+      Dst = tri_.getSubReg(Dst, DstSub);
+      if (!Dst) return false;
+      DstSub = 0;
+    }
+
+    // Eliminate SrcSub by picking a corresponding Dst superregister.
+    if (SrcSub) {
+      Dst = tri_.getMatchingSuperReg(Dst, SrcSub, MRI.getRegClass(Src));
+      if (!Dst) return false;
+      SrcSub = 0;
+    } else if (!MRI.getRegClass(Src)->contains(Dst)) {
+      return false;
+    }
+  } else {
+    // Both registers are virtual.
+
+    // Identical sub to sub.
+    if (SrcSub == DstSub)
+      SrcSub = DstSub = 0;
+    else if (SrcSub && DstSub)
+      return false; // FIXME: Qreg:ssub_3 + Dreg:ssub_1 => QReg:dsub_1 + Dreg.
+
+    // There can be no SrcSub.
+    if (SrcSub) {
+      std::swap(Src, Dst);
+      DstSub = SrcSub;
+      SrcSub = 0;
+      assert(!flipped_ && "Unexpected flip");
+      flipped_ = true;
+    }
+
+    // Find the new register class.
+    const TargetRegisterClass *SrcRC = MRI.getRegClass(Src);
+    const TargetRegisterClass *DstRC = MRI.getRegClass(Dst);
+    if (DstSub)
+      newRC_ = tri_.getMatchingSuperRegClass(DstRC, SrcRC, DstSub);
+    else
+      newRC_ = getCommonSubClass(DstRC, SrcRC);
+    if (!newRC_)
+      return false;
+  }
+  // Check our invariants
+  assert(TargetRegisterInfo::isVirtualRegister(Src) && "Src must be virtual");
+  assert(!(TargetRegisterInfo::isPhysicalRegister(Dst) && DstSub) &&
+         "Cannot have a physical SubIdx");
+  srcReg_ = Src;
+  dstReg_ = Dst;
+  subIdx_ = DstSub;
+  return true;
+}
+
+bool CoalescerPair::flip() {
+  if (subIdx_ || TargetRegisterInfo::isPhysicalRegister(dstReg_))
+    return false;
+  std::swap(srcReg_, dstReg_);
+  flipped_ = !flipped_;
+  return true;
+}
+
+bool CoalescerPair::isCoalescable(const MachineInstr *MI) const {
+  if (!MI)
+    return false;
+  unsigned Src, Dst, SrcSub, DstSub;
+  if (!isMoveInstr(MI, Src, Dst, SrcSub, DstSub))
+    return false;
+
+  // Find the virtual register that is srcReg_.
+  if (Dst == srcReg_) {
+    std::swap(Src, Dst);
+    std::swap(SrcSub, DstSub);
+  } else if (Src != srcReg_) {
+    return false;
+  }
+
+  // Now check that Dst matches dstReg_.
+  if (TargetRegisterInfo::isPhysicalRegister(dstReg_)) {
+    if (!TargetRegisterInfo::isPhysicalRegister(Dst))
+      return false;
+    assert(!subIdx_ && "Inconsistent CoalescerPair state.");
+    // DstSub could be set for a physreg from INSERT_SUBREG.
+    if (DstSub)
+      Dst = tri_.getSubReg(Dst, DstSub);
+    // Full copy of Src.
+    if (!SrcSub)
+      return dstReg_ == Dst;
+    // This is a partial register copy. Check that the parts match.
+    return tri_.getSubReg(dstReg_, SrcSub) == Dst;
+  } else {
+    // dstReg_ is virtual.
+    if (dstReg_ != Dst)
+      return false;
+    // Registers match, do the subregisters line up?
+    return compose(subIdx_, SrcSub) == DstSub;
+  }
+}
+
 // Because of the way .a files work, we must force the SimpleRC
 // implementation to be pulled in if the RegisterCoalescer classes are
 // pulled in.  Otherwise we run the risk of RegisterCoalescer being