Merge information about the number of zero, one, and sign bits of live-out registers

at phis. This enables us to eliminate a lot of pointless zexts during the DAGCombine
phase. This fixes <rdar://problem/8760114>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126170 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 54 insertions, 7 deletions

diff --git a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index 98582ba..8adaf05 100644
--- a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
@@ -127,10 +127,13 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf) {
     for (BasicBlock::const_iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
       // Mark values used outside their block as exported, by allocating
       // a virtual register for them.
-      if (isUsedOutsideOfDefiningBlock(I))
+      if (!EnableFastISel && isa<PHINode>(I)) {
+        PHIDestRegs.insert(InitializeRegForValue(I));
+      } else if (isUsedOutsideOfDefiningBlock(I)) {
         if (!isa<AllocaInst>(I) ||
             !StaticAllocaMap.count(cast<AllocaInst>(I)))
           InitializeRegForValue(I);
+      }
 
       // Collect llvm.dbg.declare information. This is done now instead of
       // during the initial isel pass through the IR so that it is done
@@ -219,6 +222,9 @@ void FunctionLoweringInfo::clear() {
   CatchInfoFound.clear();
 #endif
   LiveOutRegInfo.clear();
+  VisitedBBs.clear();
+  PHIDestRegs.clear();
+  PHISrcToDestMap.clear();
   ArgDbgValues.clear();
   ByValArgFrameIndexMap.clear();
   RegFixups.clear();
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 452f561..c1be3e9 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -644,7 +644,10 @@ SDValue RegsForValue::getCopyFromRegs(SelectionDAG &DAG,
           !RegisterVT.isInteger() || RegisterVT.isVector() ||
           !FuncInfo.LiveOutRegInfo.inBounds(Regs[Part+i]))
         continue;
-      
+
+      if (FuncInfo.PHIDestRegs.count(Regs[Part+i]) && !FuncInfo.AllPredsVisited)
+        continue;
+
       const FunctionLoweringInfo::LiveOutInfo &LOI =
         FuncInfo.LiveOutRegInfo[Regs[Part+i]];
 
@@ -6466,6 +6469,9 @@ SelectionDAGBuilder::HandlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
         }
       }
 
+      if (!EnableFastISel)
+        FuncInfo.PHISrcToDestMap[Reg] = FuncInfo.ValueMap[PN];
+
       // Remember that this register needs to added to the machine PHI node as
       // the input for this MBB.
       SmallVector<EVT, 4> ValueVTs;
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index bbc62d8..450757f 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -471,6 +471,13 @@ void SelectionDAGISel::ComputeLiveOutVRegInfo() {
     if (!TargetRegisterInfo::isVirtualRegister(DestReg))
       continue;
 
+    bool IsPHI = false;
+    DenseMap<unsigned, unsigned>::const_iterator It = FuncInfo->PHISrcToDestMap.find(DestReg);
+    if (It != FuncInfo->PHISrcToDestMap.end()) {
+      IsPHI = true;
+      DestReg = It->second;
+    }
+
     // Ignore non-scalar or non-integer values.
     SDValue Src = N->getOperand(2);
     EVT SrcVT = Src.getValueType();
@@ -482,14 +489,27 @@ void SelectionDAGISel::ComputeLiveOutVRegInfo() {
     CurDAG->ComputeMaskedBits(Src, Mask, KnownZero, KnownOne);
 
     // Only install this information if it tells us something.
-    if (NumSignBits != 1 || KnownZero != 0 || KnownOne != 0) {
-      FuncInfo->LiveOutRegInfo.grow(DestReg);
+    if (!IsPHI && NumSignBits == 1 && KnownZero == 0 && KnownOne == 0)
+      continue;
+
+    FuncInfo->LiveOutRegInfo.grow(DestReg);
+    FunctionLoweringInfo::LiveOutInfo &LOI = FuncInfo->LiveOutRegInfo[DestReg];
+
+    // If this is a PHI and there is existing information, merge it with the
+    // information from this block.
+    if (IsPHI && LOI.IsValid) {
       FunctionLoweringInfo::LiveOutInfo &LOI =
         FuncInfo->LiveOutRegInfo[DestReg];
-      LOI.NumSignBits = NumSignBits;
-      LOI.KnownOne = KnownOne;
-      LOI.KnownZero = KnownZero;
+      LOI.NumSignBits = std::min(LOI.NumSignBits, NumSignBits);
+      LOI.KnownOne &= KnownOne;
+      LOI.KnownZero &= KnownZero;
+      continue;
     }
+
+    LOI.NumSignBits = NumSignBits;
+    LOI.KnownOne = KnownOne;
+    LOI.KnownZero = KnownZero;
+    LOI.IsValid = true;
   } while (!Worklist.empty());
 }
 
@@ -840,6 +860,21 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
 #ifndef NDEBUG
     CheckLineNumbers(LLVMBB);
 #endif
+
+    if (EnableFastISel) {
+      FuncInfo->AllPredsVisited = false;
+    } else {
+      FuncInfo->AllPredsVisited = true;
+      for (const_pred_iterator PI = pred_begin(LLVMBB), PE = pred_end(LLVMBB);
+           PI != PE; ++PI) {
+        if (!FuncInfo->VisitedBBs.count(*PI)) {
+          FuncInfo->AllPredsVisited = false;
+          break;
+        }
+      }
+      FuncInfo->VisitedBBs.insert(LLVMBB);
+    }
+
     FuncInfo->MBB = FuncInfo->MBBMap[LLVMBB];
     FuncInfo->InsertPt = FuncInfo->MBB->getFirstNonPHI();