[llvm] r194286 - increase the accuracy of register pressure computation in the presence of dead definitions by using live intervals, if available, to identify dead definitions and proceed accordingly.

[Pedro Artigas]

Author: partigas
Date: Fri Nov  8 16:46:28 2013
New Revision: 194286

URL: http://llvm.org/viewvc/llvm-project?rev=194286&view=rev
Log:
increase the accuracy of register pressure computation in the presence of dead definitions by using live intervals, if available, to identify dead definitions and proceed accordingly.

Modified:
    llvm/trunk/lib/CodeGen/MachineVerifier.cpp
    llvm/trunk/lib/CodeGen/RegisterPressure.cpp

Modified: llvm/trunk/lib/CodeGen/MachineVerifier.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineVerifier.cpp?rev=194286&r1=194285&r2=194286&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineVerifier.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineVerifier.cpp Fri Nov  8 16:46:28 2013
@@ -1096,6 +1096,14 @@ void MachineVerifier::checkLiveness(cons
           report("No live segment at def", MO, MONum);
           *OS << DefIdx << " is not live in " << LI << '\n';
         }
+        // Check that, if the dead def flag is present, LiveInts agree.
+        if (MO->isDead()) {
+          LiveQueryResult LRQ = LI.Query(DefIdx);
+          if (!LRQ.isDeadDef()) {
+            report("Live range continues after dead def flag", MO, MONum);
+            *OS << "Live range: " << LI << '\n';
+          }
+        }
       } else {
         report("Virtual register has no Live interval", MO, MONum);
       }
@@ -1517,22 +1525,13 @@ void MachineVerifier::verifyLiveRangeSeg
     // A live segment can end with either a redefinition, a kill flag on a
     // use, or a dead flag on a def.
     bool hasRead = false;
-    bool hasDeadDef = false;
     for (ConstMIBundleOperands MOI(MI); MOI.isValid(); ++MOI) {
       if (!MOI->isReg() || MOI->getReg() != Reg)
         continue;
       if (MOI->readsReg())
         hasRead = true;
-      if (MOI->isDef() && MOI->isDead())
-        hasDeadDef = true;
     }
-
-    if (S.end.isDead()) {
-      if (!hasDeadDef) {
-        report("Instruction doesn't have a dead def operand", MI);
-        *OS << S << " in " << LR << '\n';
-      }
-    } else {
+    if (!S.end.isDead()) {
       if (!hasRead) {
         report("Instruction ending live segment doesn't read the register", MI);
         *OS << S << " in " << LR << '\n';

Modified: llvm/trunk/lib/CodeGen/RegisterPressure.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegisterPressure.cpp?rev=194286&r1=194285&r2=194286&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegisterPressure.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegisterPressure.cpp Fri Nov  8 16:46:28 2013
@@ -498,10 +498,20 @@ bool RegPressureTracker::recede(SmallVec
   // TODO: consider earlyclobbers?
   for (unsigned i = 0, e = RegOpers.Defs.size(); i < e; ++i) {
     unsigned Reg = RegOpers.Defs[i];
-    if (LiveRegs.erase(Reg))
-      decreaseRegPressure(Reg);
-    else
-      discoverLiveOut(Reg);
+    bool DeadDef = false;
+    if (RequireIntervals) {
+      const LiveRange *LR = getLiveRange(Reg);
+      if (LR) {
+        LiveQueryResult LRQ = LR->Query(SlotIdx);
+        DeadDef = LRQ.isDeadDef();
+      }
+    }
+    if (!DeadDef) {
+      if (LiveRegs.erase(Reg))
+        decreaseRegPressure(Reg);
+      else
+        discoverLiveOut(Reg);
+    }
   }
 
   // Generate liveness for uses.
@@ -702,8 +712,19 @@ void RegPressureTracker::bumpUpwardPress
   // Kill liveness at live defs.
   for (unsigned i = 0, e = RegOpers.Defs.size(); i < e; ++i) {
     unsigned Reg = RegOpers.Defs[i];
-    if (!containsReg(RegOpers.Uses, Reg))
-      decreaseRegPressure(Reg);
+    bool DeadDef = false;
+    if (RequireIntervals) {
+      const LiveRange *LR = getLiveRange(Reg);
+      if (LR) {
+        SlotIndex SlotIdx = LIS->getInstructionIndex(MI);
+        LiveQueryResult LRQ = LR->Query(SlotIdx);
+        DeadDef = LRQ.isDeadDef();
+      }
+    }
+    if (!DeadDef) {
+      if (!containsReg(RegOpers.Uses, Reg))
+        decreaseRegPressure(Reg);
+    }
   }
   // Generate liveness for uses.
   for (unsigned i = 0, e = RegOpers.Uses.size(); i < e; ++i) {