[llvm] r233395 - [RegisterCoalescer] Refine the terminal rule to still consider the terminal

[Quentin Colombet]

Author: qcolombet
Date: Fri Mar 27 13:37:15 2015
New Revision: 233395

URL: http://llvm.org/viewvc/llvm-project?rev=233395&view=rev
Log:
[RegisterCoalescer] Refine the terminal rule to still consider the terminal
nodes.
When a node is terminal it is pushed at the end of the list of the copies to
coalesce instead of being completely ignored. In effect, this reduces its
priority over non-terminal nodes.

Because of that, we do not miss the rematerialization opportunities, nor the
copies that can be merged with more complex, than the terminal rule,
interference checks.

Related to PR22768.

Modified:
    llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp
    llvm/trunk/test/CodeGen/X86/sret-implicit.ll

Modified: llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp?rev=233395&r1=233394&r2=233395&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp Fri Mar 27 13:37:15 2015
@@ -2733,13 +2733,17 @@ bool RegisterCoalescer::applyTerminalRul
     return false;
   // Check if the destination of this copy has any other affinity.
   unsigned DstReg = Copy.getOperand(0).getReg();
+  unsigned SrcReg = Copy.getOperand(1).getReg();
   if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
+      // If SrcReg is a physical register, the copy won't be coalesced.
+      // Ignoring it may have other side effect (like missing
+      // rematerialization). So keep it.
+      TargetRegisterInfo::isPhysicalRegister(SrcReg) ||
       !isTerminalReg(DstReg, Copy, MRI))
     return false;
 
   // DstReg is a terminal node. Check if it inteferes with any other
   // copy involving SrcReg.
-  unsigned SrcReg = Copy.getOperand(1).getReg();
   const MachineBasicBlock *OrigBB = Copy.getParent();
   const LiveInterval &DstLI = LIS->getInterval(DstReg);
   for (const MachineInstr &MI : MRI->reg_nodbg_instructions(SrcReg)) {
@@ -2775,25 +2779,45 @@ RegisterCoalescer::copyCoalesceInMBB(Mac
   // yet, it might invalidate the iterator.
   const unsigned PrevSize = WorkList.size();
   if (JoinGlobalCopies) {
+    SmallVector<MachineInstr*, 2> LocalTerminals;
+    SmallVector<MachineInstr*, 2> GlobalTerminals;
     // Coalesce copies bottom-up to coalesce local defs before local uses. They
     // are not inherently easier to resolve, but slightly preferable until we
     // have local live range splitting. In particular this is required by
     // cmp+jmp macro fusion.
     for (MachineBasicBlock::iterator MII = MBB->begin(), E = MBB->end();
          MII != E; ++MII) {
-      if (!MII->isCopyLike() || applyTerminalRule(*MII))
+      if (!MII->isCopyLike())
         continue;
-      if (isLocalCopy(&(*MII), LIS))
-        LocalWorkList.push_back(&(*MII));
-      else
-        WorkList.push_back(&(*MII));
+      bool ApplyTerminalRule = applyTerminalRule(*MII);
+      if (isLocalCopy(&(*MII), LIS)) {
+        if (ApplyTerminalRule)
+          LocalTerminals.push_back(&(*MII));
+        else
+          LocalWorkList.push_back(&(*MII));
+      } else {
+        if (ApplyTerminalRule)
+          GlobalTerminals.push_back(&(*MII));
+        else
+          WorkList.push_back(&(*MII));
+      }
     }
+    // Append the copies evicted by the terminal rule at the end of the list.
+    LocalWorkList.append(LocalTerminals.begin(), LocalTerminals.end());
+    WorkList.append(GlobalTerminals.begin(), GlobalTerminals.end());
   }
   else {
+    SmallVector<MachineInstr*, 2> Terminals;
      for (MachineBasicBlock::iterator MII = MBB->begin(), E = MBB->end();
           MII != E; ++MII)
-       if (MII->isCopyLike() && !applyTerminalRule(*MII))
-         WorkList.push_back(MII);
+       if (MII->isCopyLike()) {
+        if (applyTerminalRule(*MII))
+          Terminals.push_back(&(*MII));
+        else
+          WorkList.push_back(MII);
+       }
+     // Append the copies evicted by the terminal rule at the end of the list.
+     WorkList.append(Terminals.begin(), Terminals.end());
   }
   // Try coalescing the collected copies immediately, and remove the nulls.
   // This prevents the WorkList from getting too large since most copies are

Modified: llvm/trunk/test/CodeGen/X86/sret-implicit.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/sret-implicit.ll?rev=233395&r1=233394&r2=233395&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/sret-implicit.ll (original)
+++ llvm/trunk/test/CodeGen/X86/sret-implicit.ll Fri Mar 27 13:37:15 2015
@@ -1,5 +1,7 @@
 ; RUN: llc -mtriple=x86_64-apple-darwin8 < %s | FileCheck %s
 ; RUN: llc -mtriple=x86_64-pc-linux < %s | FileCheck %s
+; RUN: llc -mtriple=x86_64-apple-darwin8 -terminal-rule < %s | FileCheck %s
+; RUN: llc -mtriple=x86_64-pc-linux -terminal-rule < %s | FileCheck %s
 
 ; CHECK-LABEL: return32
 ; CHECK-DAG: movq	$0, (%rdi)