Also attempt trivial coalescing for live intervals that end in a copy.

The coalescer is supposed to clean these up, but when setting up parameters
for a function call, there may be copies to physregs. If the defining
instruction has been LICM'ed far away, the coalescer won't touch it.

The register allocation hint does not always work - when the register
allocator is backtracking, it clears the hints.

This patch takes care of a few more cases that r90163 missed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90502 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 48 insertions, 44 deletions

diff --git a/lib/CodeGen/RegAllocLinearScan.cpp b/lib/CodeGen/RegAllocLinearScan.cpp
index 4ff512932f..79bde1611f 100644
--- a/lib/CodeGen/RegAllocLinearScan.cpp
+++ b/lib/CodeGen/RegAllocLinearScan.cpp
@@ -390,66 +390,70 @@ void RALinScan::ComputeRelatedRegClasses() {
         RelatedRegClasses.unionSets(I->second, OneClassForEachPhysReg[*AS]);
 }
 
-/// attemptTrivialCoalescing - If a simple interval is defined by a copy,
-/// try allocate the definition the same register as the source register
-/// if the register is not defined during live time of the interval. This
-/// eliminate a copy. This is used to coalesce copies which were not
-/// coalesced away before allocation either due to dest and src being in
-/// different register classes or because the coalescer was overly
-/// conservative.
+/// attemptTrivialCoalescing - If a simple interval is defined by a copy, try
+/// allocate the definition the same register as the source register if the
+/// register is not defined during live time of the interval. If the interval is
+/// killed by a copy, try to use the destination register. This eliminates a
+/// copy. This is used to coalesce copies which were not coalesced away before
+/// allocation either due to dest and src being in different register classes or
+/// because the coalescer was overly conservative.
 unsigned RALinScan::attemptTrivialCoalescing(LiveInterval &cur, unsigned Reg) {
   unsigned Preference = vrm_->getRegAllocPref(cur.reg);
   if ((Preference && Preference == Reg) || !cur.containsOneValue())
     return Reg;
 
   VNInfo *vni = cur.begin()->valno;
-  if ((vni->def == SlotIndex()) ||
-      vni->isUnused() || !vni->isDefAccurate())
+  if (vni->isUnused())
     return Reg;
-  MachineInstr *CopyMI = li_->getInstructionFromIndex(vni->def);
-  unsigned SrcReg, DstReg, SrcSubReg, DstSubReg, PhysReg;
-  if (!CopyMI ||
-      !tii_->isMoveInstr(*CopyMI, SrcReg, DstReg, SrcSubReg, DstSubReg))
-    return Reg;
-  PhysReg = SrcReg;
-  if (TargetRegisterInfo::isVirtualRegister(SrcReg)) {
-    if (!vrm_->isAssignedReg(SrcReg))
+  unsigned CandReg;
+  bool forward;                 // extending physreg forward
+  {
+    MachineInstr *CopyMI;
+    unsigned SrcReg, DstReg, SrcSubReg, DstSubReg;
+    if (vni->def != SlotIndex() && vni->isDefAccurate() &&
+        (CopyMI = li_->getInstructionFromIndex(vni->def)) &&
+        tii_->isMoveInstr(*CopyMI, SrcReg, DstReg, SrcSubReg, DstSubReg))
+      // Defined by a copy, try to extend SrcReg forward
+      CandReg = SrcReg, forward = true;
+    else if (cur.ranges.size()==1 &&
+             (CopyMI =
+              li_->getInstructionFromIndex(cur.begin()->end.getBaseIndex())) &&
+             tii_->isMoveInstr(*CopyMI, SrcReg, DstReg, SrcSubReg, DstSubReg) &&
+             cur.reg == SrcReg)
+      // Only used by a copy, try to extend DstReg backwards
+      CandReg = DstReg, forward = false;
+    else
+      return Reg;
+  }
+
+  if (TargetRegisterInfo::isVirtualRegister(CandReg)) {
+    if (!vrm_->isAssignedReg(CandReg))
       return Reg;
-    PhysReg = vrm_->getPhys(SrcReg);
+    CandReg = vrm_->getPhys(CandReg);
   }
-  if (Reg == PhysReg)
+  if (Reg == CandReg)
     return Reg;
 
   const TargetRegisterClass *RC = mri_->getRegClass(cur.reg);
-  if (!RC->contains(PhysReg))
+  if (!RC->contains(CandReg))
     return Reg;
 
-  // Try to coalesce.
-  if (!li_->conflictsWithPhysRegDef(cur, *vrm_, PhysReg)) {
-    DEBUG(errs() << "Coalescing: " << cur << " -> " << tri_->getName(PhysReg)
-                 << '\n');
-    vrm_->clearVirt(cur.reg);
-    vrm_->assignVirt2Phys(cur.reg, PhysReg);
-
-    // Remove unnecessary kills since a copy does not clobber the register.
-    if (li_->hasInterval(SrcReg)) {
-      LiveInterval &SrcLI = li_->getInterval(SrcReg);
-      for (MachineRegisterInfo::use_iterator I = mri_->use_begin(cur.reg),
-             E = mri_->use_end(); I != E; ++I) {
-        MachineOperand &O = I.getOperand();
-        if (!O.isKill())
-          continue;
-        MachineInstr *MI = &*I;
-        if (SrcLI.liveAt(li_->getInstructionIndex(MI).getDefIndex()))
-          O.setIsKill(false);
-      }
-    }
-
-    ++NumCoalesce;
-    return PhysReg;
+  if (forward) {
+    if (li_->conflictsWithPhysRegDef(cur, *vrm_, CandReg))
+      return Reg;
+  } else {
+    if (li_->conflictsWithPhysRegUse(cur, *vrm_, CandReg))
+      return Reg;
   }
 
-  return Reg;
+  // Try to coalesce.
+  DEBUG(errs() << "Coalescing: " << cur << " -> " << tri_->getName(CandReg)
+        << '\n');
+  vrm_->clearVirt(cur.reg);
+  vrm_->assignVirt2Phys(cur.reg, CandReg);
+
+  ++NumCoalesce;
+  return CandReg;
 }
 
 bool RALinScan::runOnMachineFunction(MachineFunction &fn) {