Replace analyzeSiblingValues with new algorithm to fix its compile

time issue. The patch is to solve PR17409 and its duplicates.

analyzeSiblingValues is a N x N complexity algorithm where N is
the number of siblings generated by reg splitting. Although it
causes siginificant compile time issue when N is large, it is also
important for performance since it removes redundent spills and
enables rematerialization.

To solve the compile time issue, the patch removes analyzeSiblingValues
and replaces it with lower cost alternatives containing two parts. The
first part creates a new spill hoisting method in postOptimization of
register allocation. It does spill hoisting at once after all the spills
are generated instead of inside every instance of selectOrSplit. The
second part queries the define expr of the original register for
rematerializaiton and keep it always available during register allocation
even if it is already dead. It deletes those dead instructions only in
postOptimization. With the two parts in the patch, it can remove
analyzeSiblingValues without sacrificing performance.

Differential Revision: http://reviews.llvm.org/D15302



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265309 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 43 insertions, 20 deletions

diff --git a/lib/CodeGen/LiveRangeEdit.cpp b/lib/CodeGen/LiveRangeEdit.cpp
index 72eafcd0792..5610c5afa0d 100644
--- a/lib/CodeGen/LiveRangeEdit.cpp
+++ b/lib/CodeGen/LiveRangeEdit.cpp
@@ -63,10 +63,13 @@ void LiveRangeEdit::scanRemattable(AliasAnalysis *aa) {
   for (VNInfo *VNI : getParent().valnos) {
     if (VNI->isUnused())
       continue;
-    MachineInstr *DefMI = LIS.getInstructionFromIndex(VNI->def);
+    unsigned Original = VRM->getOriginal(getReg());
+    LiveInterval &OrigLI = LIS.getInterval(Original);
+    VNInfo *OrigVNI = OrigLI.getVNInfoAt(VNI->def);
+    MachineInstr *DefMI = LIS.getInstructionFromIndex(OrigVNI->def);
     if (!DefMI)
       continue;
-    checkRematerializable(VNI, DefMI, aa);
+    checkRematerializable(OrigVNI, DefMI, aa);
   }
   ScannedRemattable = true;
 }
@@ -113,24 +116,18 @@ bool LiveRangeEdit::allUsesAvailableAt(const MachineInstr *OrigMI,
   return true;
 }
 
-bool LiveRangeEdit::canRematerializeAt(Remat &RM,
-                                       SlotIndex UseIdx,
-                                       bool cheapAsAMove) {
+bool LiveRangeEdit::canRematerializeAt(Remat &RM, VNInfo *OrigVNI,
+                                       SlotIndex UseIdx, bool cheapAsAMove) {
   assert(ScannedRemattable && "Call anyRematerializable first");
 
   // Use scanRemattable info.
-  if (!Remattable.count(RM.ParentVNI))
+  if (!Remattable.count(OrigVNI))
     return false;
 
   // No defining instruction provided.
   SlotIndex DefIdx;
-  if (RM.OrigMI)
-    DefIdx = LIS.getInstructionIndex(*RM.OrigMI);
-  else {
-    DefIdx = RM.ParentVNI->def;
-    RM.OrigMI = LIS.getInstructionFromIndex(DefIdx);
-    assert(RM.OrigMI && "No defining instruction for remattable value");
-  }
+  assert(RM.OrigMI && "No defining instruction for remattable value");
+  DefIdx = LIS.getInstructionIndex(*RM.OrigMI);
 
   // If only cheap remats were requested, bail out early.
   if (cheapAsAMove && !TII.isAsCheapAsAMove(RM.OrigMI))
@@ -261,6 +258,15 @@ void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
   // Collect virtual registers to be erased after MI is gone.
   SmallVector<unsigned, 8> RegsToErase;
   bool ReadsPhysRegs = false;
+  bool isOrigDef = false;
+  unsigned Dest;
+  if (VRM && MI->getOperand(0).isReg()) {
+    Dest = MI->getOperand(0).getReg();
+    unsigned Original = VRM->getOriginal(Dest);
+    LiveInterval &OrigLI = LIS.getInterval(Original);
+    VNInfo *OrigVNI = OrigLI.getVNInfoAt(Idx);
+    isOrigDef = SlotIndex::isSameInstr(OrigVNI->def, Idx);
+  }
 
   // Check for live intervals that may shrink
   for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
@@ -314,11 +320,24 @@ void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
     }
     DEBUG(dbgs() << "Converted physregs to:\t" << *MI);
   } else {
-    if (TheDelegate)
-      TheDelegate->LRE_WillEraseInstruction(MI);
-    LIS.RemoveMachineInstrFromMaps(*MI);
-    MI->eraseFromParent();
-    ++NumDCEDeleted;
+    // If the dest of MI is an original reg, don't delete the inst. Replace
+    // the dest with a new reg, keep the inst for remat of other siblings.
+    // The inst is saved in LiveRangeEdit::DeadRemats and will be deleted
+    // after all the allocations of the func are done.
+    if (isOrigDef) {
+      unsigned NewDest = createFrom(Dest);
+      pop_back();
+      markDeadRemat(MI);
+      const TargetRegisterInfo &TRI = *MRI.getTargetRegisterInfo();
+      MI->substituteRegister(Dest, NewDest, 0, TRI);
+      MI->getOperand(0).setIsDead(false);
+    } else {
+      if (TheDelegate)
+        TheDelegate->LRE_WillEraseInstruction(MI);
+      LIS.RemoveMachineInstrFromMaps(*MI);
+      MI->eraseFromParent();
+      ++NumDCEDeleted;
+    }
   }
 
   // Erase any virtregs that are now empty and unused. There may be <undef>
@@ -332,8 +351,9 @@ void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
   }
 }
 
-void LiveRangeEdit::eliminateDeadDefs(SmallVectorImpl<MachineInstr*> &Dead,
-                                      ArrayRef<unsigned> RegsBeingSpilled) {
+void LiveRangeEdit::eliminateDeadDefs(SmallVectorImpl<MachineInstr *> &Dead,
+                                      ArrayRef<unsigned> RegsBeingSpilled,
+                                      bool NoSplit) {
   ToShrinkSet ToShrink;
 
   for (;;) {
@@ -355,6 +375,9 @@ void LiveRangeEdit::eliminateDeadDefs(SmallVectorImpl<MachineInstr*> &Dead,
     if (!LIS.shrinkToUses(LI, &Dead))
       continue;
 
+    if (NoSplit)
+      continue;
+
     // Don't create new intervals for a register being spilled.
     // The new intervals would have to be spilled anyway so its not worth it.
     // Also they currently aren't spilled so creating them and not spilling