[PATCH] D30173: [ExecutionDepsFix] Don't revisit true dependencies

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This revision was automatically updated to reflect the committed changes.
Closed by commit rL299467: [ExecutionDepsFix] Don't revisit true dependencies (authored by kfischer).

Changed prior to commit:
  https://reviews.llvm.org/D30173?vs=89131&id=94113#toc

Repository:
  rL LLVM

https://reviews.llvm.org/D30173

Files:
  llvm/trunk/include/llvm/CodeGen/ExecutionDepsFix.h
  llvm/trunk/lib/CodeGen/ExecutionDepsFix.cpp


Index: llvm/trunk/include/llvm/CodeGen/ExecutionDepsFix.h
===================================================================
--- llvm/trunk/include/llvm/CodeGen/ExecutionDepsFix.h
+++ llvm/trunk/include/llvm/CodeGen/ExecutionDepsFix.h
@@ -210,7 +210,7 @@
   void processDefs(MachineInstr *, bool breakDependency, bool Kill);
   void visitSoftInstr(MachineInstr*, unsigned mask);
   void visitHardInstr(MachineInstr*, unsigned domain);
-  void pickBestRegisterForUndef(MachineInstr *MI, unsigned OpIdx,
+  bool pickBestRegisterForUndef(MachineInstr *MI, unsigned OpIdx,
                                 unsigned Pref);
   bool shouldBreakDependence(MachineInstr*, unsigned OpIdx, unsigned Pref);
   void processUndefReads(MachineBasicBlock*);
Index: llvm/trunk/lib/CodeGen/ExecutionDepsFix.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/ExecutionDepsFix.cpp
+++ llvm/trunk/lib/CodeGen/ExecutionDepsFix.cpp
@@ -288,16 +288,18 @@
 /// \brief Helps avoid false dependencies on undef registers by updating the
 /// machine instructions' undef operand to use a register that the instruction
 /// is truly dependent on, or use a register with clearance higher than Pref.
-void ExecutionDepsFix::pickBestRegisterForUndef(MachineInstr *MI,
-    unsigned OpIdx, unsigned Pref) {
+/// Returns true if it was able to find a true dependency, thus not requiring
+/// a dependency breaking instruction regardless of clearance.
+bool ExecutionDepsFix::pickBestRegisterForUndef(MachineInstr *MI,
+                                                unsigned OpIdx, unsigned Pref) {
   MachineOperand &MO = MI->getOperand(OpIdx);
   assert(MO.isUndef() && "Expected undef machine operand");
 
   unsigned OriginalReg = MO.getReg();
 
   // Update only undef operands that are mapped to one register.
   if (AliasMap[OriginalReg].size() != 1)
-    return;
+    return false;
 
   // Get the undef operand's register class
   const TargetRegisterClass *OpRC =
@@ -312,7 +314,7 @@
     // We found a true dependency - replace the undef register with the true
     // dependency.
     MO.setReg(CurrMO.getReg());
-    return;
+    return true;
   }
 
   // Go over all registers in the register class and find the register with
@@ -337,6 +339,8 @@
   // Update the operand if we found a register with better clearance.
   if (MaxClearanceReg != OriginalReg)
     MO.setReg(MaxClearanceReg);
+
+  return false;
 }
 
 /// \brief Return true to if it makes sense to break dependence on a partial def
@@ -371,8 +375,11 @@
   if (breakDependency) {
     unsigned Pref = TII->getUndefRegClearance(*MI, OpNum, TRI);
     if (Pref) {
-      pickBestRegisterForUndef(MI, OpNum, Pref);
-      if (shouldBreakDependence(MI, OpNum, Pref))
+      bool HadTrueDependency = pickBestRegisterForUndef(MI, OpNum, Pref);
+      // We don't need to bother trying to break a dependency if this
+      // instruction has a true dependency on that register through another
+      // operand - we'll have to wait for it to be available regardless.
+      if (!HadTrueDependency && shouldBreakDependence(MI, OpNum, Pref))
         UndefReads.push_back(std::make_pair(MI, OpNum));
     }
   }


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