Allow dead insts to be kept in DeadRemat only when they are rematerializable.

Because isReallyTriviallyReMaterializableGeneric puts many limits on
rematerializable instructions, this fix can prevent instructions with
tied virtual operands and instructions with virtual register uses from
being kept in DeadRemat, so as to workaround the live interval consistency
problem for the dummy instructions kept in DeadRemat.

But we still need to fix the live interval consistency problem. This patch
is just a short time relieve. PR28464 has been filed as a reminder.

Differential Revision: http://reviews.llvm.org/D19486

llvm-svn: 274928

diff --git a/llvm/include/llvm/CodeGen/LiveRangeEdit.h b/llvm/include/llvm/CodeGen/LiveRangeEdit.h
index 0c1e794..4250777 100644 (file)
--- a/llvm/include/llvm/CodeGen/LiveRangeEdit.h
+++ b/llvm/include/llvm/CodeGen/LiveRangeEdit.h
@@ -100,7 +100,8 @@ private:
                     SmallVector<LiveInterval*, 8>,
                     SmallPtrSet<LiveInterval*, 8> > ToShrinkSet;
   /// Helper for eliminateDeadDefs.
-  void eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink);
+  void eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink,
+                        AliasAnalysis *AA);
 
   /// MachineRegisterInfo callback to notify when new virtual
   /// registers are created.
@@ -242,7 +243,8 @@ public:
   /// allocator.  These registers should not be split into new intervals
   /// as currently those new intervals are not guaranteed to spill.
   void eliminateDeadDefs(SmallVectorImpl<MachineInstr *> &Dead,
-                         ArrayRef<unsigned> RegsBeingSpilled = None);
+                         ArrayRef<unsigned> RegsBeingSpilled = None,
+                         AliasAnalysis *AA = nullptr);
 
   /// calculateRegClassAndHint - Recompute register class and hint for each new
   /// register.

diff --git a/llvm/lib/CodeGen/InlineSpiller.cpp b/llvm/lib/CodeGen/InlineSpiller.cpp
index 92fe577..197db77 100644 (file)
--- a/llvm/lib/CodeGen/InlineSpiller.cpp
+++ b/llvm/lib/CodeGen/InlineSpiller.cpp
@@ -626,7 +626,7 @@ void InlineSpiller::reMaterializeAll() {
   if (DeadDefs.empty())
     return;
   DEBUG(dbgs() << "Remat created " << DeadDefs.size() << " dead defs.\n");
-  Edit->eliminateDeadDefs(DeadDefs, RegsToSpill);
+  Edit->eliminateDeadDefs(DeadDefs, RegsToSpill, AA);
 
   // LiveRangeEdit::eliminateDeadDef is used to remove dead define instructions
   // after rematerialization.  To remove a VNI for a vreg from its LiveInterval,
@@ -996,7 +996,7 @@ void InlineSpiller::spillAll() {
   // Hoisted spills may cause dead code.
   if (!DeadDefs.empty()) {
     DEBUG(dbgs() << "Eliminating " << DeadDefs.size() << " dead defs\n");
-    Edit->eliminateDeadDefs(DeadDefs, RegsToSpill);
+    Edit->eliminateDeadDefs(DeadDefs, RegsToSpill, AA);
   }
 
   // Finally delete the SnippetCopies.
@@ -1440,7 +1440,7 @@ void HoistSpillHelper::hoistAllSpills() {
           RMEnt->RemoveOperand(i - 1);
       }
     }
-    Edit.eliminateDeadDefs(SpillsToRm, None);
+    Edit.eliminateDeadDefs(SpillsToRm, None, AA);
   }
 }
 

diff --git a/llvm/lib/CodeGen/LiveRangeEdit.cpp b/llvm/lib/CodeGen/LiveRangeEdit.cpp
index 20003dd..b35c0ad 100644 (file)
--- a/llvm/lib/CodeGen/LiveRangeEdit.cpp
+++ b/llvm/lib/CodeGen/LiveRangeEdit.cpp
@@ -234,7 +234,8 @@ bool LiveRangeEdit::useIsKill(const LiveInterval &LI,
 }
 
 /// Find all live intervals that need to shrink, then remove the instruction.
-void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
+void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink,
+                                     AliasAnalysis *AA) {
   assert(MI->allDefsAreDead() && "Def isn't really dead");
   SlotIndex Idx = LIS.getInstructionIndex(*MI).getRegSlot();
 
@@ -327,11 +328,12 @@ void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
     }
     DEBUG(dbgs() << "Converted physregs to:\t" << *MI);
   } else {
-    // 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) {
+    // If the dest of MI is an original reg and MI is reMaterializable,
+    // don't delete the inst. Replace the dest with a new reg, and 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 && DeadRemats && TII.isTriviallyReMaterializable(*MI, AA)) {
       LiveInterval &NewLI = createEmptyIntervalFrom(Dest);
       VNInfo *VNI = NewLI.getNextValue(Idx, LIS.getVNInfoAllocator());
       NewLI.addSegment(LiveInterval::Segment(Idx, Idx.getDeadSlot(), VNI));
@@ -361,13 +363,14 @@ void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
 }
 
 void LiveRangeEdit::eliminateDeadDefs(SmallVectorImpl<MachineInstr *> &Dead,
-                                      ArrayRef<unsigned> RegsBeingSpilled) {
+                                      ArrayRef<unsigned> RegsBeingSpilled,
+                                      AliasAnalysis *AA) {
   ToShrinkSet ToShrink;
 
   for (;;) {
     // Erase all dead defs.
     while (!Dead.empty())
-      eliminateDeadDef(Dead.pop_back_val(), ToShrink);
+      eliminateDeadDef(Dead.pop_back_val(), ToShrink, AA);
 
     if (ToShrink.empty())
       break;

diff --git a/llvm/lib/CodeGen/RegAllocGreedy.cpp b/llvm/lib/CodeGen/RegAllocGreedy.cpp
index 4736da6..c4d4b1e 100644 (file)
--- a/llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ b/llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -129,6 +129,7 @@ class RAGreedy : public MachineFunctionPass,
   EdgeBundles *Bundles;
   SpillPlacement *SpillPlacer;
   LiveDebugVariables *DebugVars;
+  AliasAnalysis *AA;
 
   // state
   std::unique_ptr<Spiller> SpillerInstance;
@@ -2592,6 +2593,7 @@ bool RAGreedy::runOnMachineFunction(MachineFunction &mf) {
   Bundles = &getAnalysis<EdgeBundles>();
   SpillPlacer = &getAnalysis<SpillPlacement>();
   DebugVars = &getAnalysis<LiveDebugVariables>();
+  AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
 
   initializeCSRCost();
 
@@ -2600,7 +2602,7 @@ bool RAGreedy::runOnMachineFunction(MachineFunction &mf) {
   DEBUG(LIS->dump());
 
   SA.reset(new SplitAnalysis(*VRM, *LIS, *Loops));
-  SE.reset(new SplitEditor(*SA, *LIS, *VRM, *DomTree, *MBFI));
+  SE.reset(new SplitEditor(*SA, *AA, *LIS, *VRM, *DomTree, *MBFI));
   ExtraRegInfo.clear();
   ExtraRegInfo.resize(MRI->getNumVirtRegs());
   NextCascade = 1;

diff --git a/llvm/lib/CodeGen/SplitKit.cpp b/llvm/lib/CodeGen/SplitKit.cpp
index c309971..07be24b 100644 (file)
--- a/llvm/lib/CodeGen/SplitKit.cpp
+++ b/llvm/lib/CodeGen/SplitKit.cpp
@@ -338,11 +338,13 @@ void SplitAnalysis::analyze(const LiveInterval *li) {
 //===----------------------------------------------------------------------===//
 
 /// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
-SplitEditor::SplitEditor(SplitAnalysis &sa, LiveIntervals &lis, VirtRegMap &vrm,
+SplitEditor::SplitEditor(SplitAnalysis &sa, AliasAnalysis &aa,
+                         LiveIntervals &lis, VirtRegMap &vrm,
                          MachineDominatorTree &mdt,
                          MachineBlockFrequencyInfo &mbfi)
-    : SA(sa), LIS(lis), VRM(vrm), MRI(vrm.getMachineFunction().getRegInfo()),
-      MDT(mdt), TII(*vrm.getMachineFunction().getSubtarget().getInstrInfo()),
+    : SA(sa), AA(aa), LIS(lis), VRM(vrm),
+      MRI(vrm.getMachineFunction().getRegInfo()), MDT(mdt),
+      TII(*vrm.getMachineFunction().getSubtarget().getInstrInfo()),
       TRI(*vrm.getMachineFunction().getSubtarget().getRegisterInfo()),
       MBFI(mbfi), Edit(nullptr), OpenIdx(0), SpillMode(SM_Partition),
       RegAssign(Allocator) {}
@@ -1130,7 +1132,7 @@ void SplitEditor::deleteRematVictims() {
   if (Dead.empty())
     return;
 
-  Edit->eliminateDeadDefs(Dead);
+  Edit->eliminateDeadDefs(Dead, None, &AA);
 }
 
 void SplitEditor::finish(SmallVectorImpl<unsigned> *LRMap) {

diff --git a/llvm/lib/CodeGen/SplitKit.h b/llvm/lib/CodeGen/SplitKit.h
index 749019b..a968494 100644 (file)
--- a/llvm/lib/CodeGen/SplitKit.h
+++ b/llvm/lib/CodeGen/SplitKit.h
@@ -235,6 +235,7 @@ public:
 ///
 class LLVM_LIBRARY_VISIBILITY SplitEditor {
   SplitAnalysis &SA;
+  AliasAnalysis &AA;
   LiveIntervals &LIS;
   VirtRegMap &VRM;
   MachineRegisterInfo &MRI;
@@ -380,8 +381,9 @@ private:
 public:
   /// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
   /// Newly created intervals will be appended to newIntervals.
-  SplitEditor(SplitAnalysis &SA, LiveIntervals&, VirtRegMap&,
-              MachineDominatorTree&, MachineBlockFrequencyInfo &);
+  SplitEditor(SplitAnalysis &SA, AliasAnalysis &AA, LiveIntervals&,
+              VirtRegMap&, MachineDominatorTree&,
+              MachineBlockFrequencyInfo &);
 
   /// reset - Prepare for a new split.
   void reset(LiveRangeEdit&, ComplementSpillMode = SM_Partition);