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>.

llvm-svn: 126380

include/llvm/CodeGen/FunctionLoweringInfo.h

@@ -159,6 +159,13 @@ public:
     return LOI;
   }
 
+  /// GetLiveOutRegInfo - Gets LiveOutInfo for a register, returning NULL if the
+  /// register is a PHI destination and the PHI's LiveOutInfo is not valid. If
+  /// the register's LiveOutInfo is for a smaller bit width, it is extended to
+  /// the larger bit width by zero extension. The bit width must be no smaller
+  /// than the LiveOutInfo's existing bit width.
+  const LiveOutInfo *GetLiveOutRegInfo(unsigned Reg, unsigned BitWidth);
+
   /// AddLiveOutRegInfo - Adds LiveOutInfo for a register.
   void AddLiveOutRegInfo(unsigned Reg, unsigned NumSignBits,
                          const APInt &KnownZero, const APInt &KnownOne) {
@@ -173,6 +180,10 @@ public:
     LOI.KnownZero = KnownZero;
   }
 
+  /// ComputePHILiveOutRegInfo - Compute LiveOutInfo for a PHI's destination
+  /// register based on the LiveOutInfo of its operands.
+  void ComputePHILiveOutRegInfo(const PHINode*);
+
   /// InvalidatePHILiveOutRegInfo - Invalidates a PHI's LiveOutInfo, to be
   /// called when a block is visited before all of its predecessors.
   void InvalidatePHILiveOutRegInfo(const PHINode *PN) {

lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp

@@ -255,6 +255,122 @@ unsigned FunctionLoweringInfo::CreateRegs(const Type *Ty) {
   return FirstReg;
 }
 
+/// GetLiveOutRegInfo - Gets LiveOutInfo for a register, returning NULL if the
+/// register is a PHI destination and the PHI's LiveOutInfo is not valid. If
+/// the register's LiveOutInfo is for a smaller bit width, it is extended to
+/// the larger bit width by zero extension. The bit width must be no smaller
+/// than the LiveOutInfo's existing bit width.
+const FunctionLoweringInfo::LiveOutInfo *
+FunctionLoweringInfo::GetLiveOutRegInfo(unsigned Reg, unsigned BitWidth) {
+  if (!LiveOutRegInfo.inBounds(Reg))
+    return NULL;
+
+  LiveOutInfo *LOI = &LiveOutRegInfo[Reg];
+  if (!LOI->IsValid)
+    return NULL;
+
+  if (BitWidth >= LOI->KnownZero.getBitWidth()) {
+    LOI->KnownZero = LOI->KnownZero.zextOrTrunc(BitWidth);
+    LOI->KnownOne = LOI->KnownOne.zextOrTrunc(BitWidth);
+  }
+
+  return LOI;
+}
+
+/// ComputePHILiveOutRegInfo - Compute LiveOutInfo for a PHI's destination
+/// register based on the LiveOutInfo of its operands.
+void FunctionLoweringInfo::ComputePHILiveOutRegInfo(const PHINode *PN) {
+  const Type *Ty = PN->getType();
+  if (!Ty->isIntegerTy() || Ty->isVectorTy())
+    return;
+
+  SmallVector<EVT, 1> ValueVTs;
+  ComputeValueVTs(TLI, Ty, ValueVTs);
+  assert(ValueVTs.size() == 1 &&
+         "PHIs with non-vector integer types should have a single VT.");
+  EVT IntVT = ValueVTs[0];
+
+  if (TLI.getNumRegisters(PN->getContext(), IntVT) != 1)
+    return;
+  IntVT = TLI.getTypeToTransformTo(PN->getContext(), IntVT);
+  unsigned BitWidth = IntVT.getSizeInBits();
+
+  unsigned DestReg = ValueMap[PN];
+  if (!TargetRegisterInfo::isVirtualRegister(DestReg))
+    return;
+  LiveOutRegInfo.grow(DestReg);
+  LiveOutInfo &DestLOI = LiveOutRegInfo[DestReg];
+
+  Value *V = PN->getIncomingValue(0);
+  if (isa<UndefValue>(V) || isa<ConstantExpr>(V)) {
+    DestLOI.NumSignBits = 1;
+    APInt Zero(BitWidth, 0);
+    DestLOI.KnownZero = Zero;
+    DestLOI.KnownOne = Zero;
+    return;
+  }
+
+  if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
+    APInt Val = CI->getValue().zextOrTrunc(BitWidth);
+    DestLOI.NumSignBits = Val.getNumSignBits();
+    DestLOI.KnownZero = ~Val;
+    DestLOI.KnownOne = Val;
+  } else {
+    assert(ValueMap.count(V) && "V should have been placed in ValueMap when its"
+                                "CopyToReg node was created.");
+    unsigned SrcReg = ValueMap[V];
+    if (!TargetRegisterInfo::isVirtualRegister(SrcReg)) {
+      DestLOI.IsValid = false;
+      return;
+    }
+    const LiveOutInfo *SrcLOI = GetLiveOutRegInfo(SrcReg, BitWidth);
+    if (!SrcLOI) {
+      DestLOI.IsValid = false;
+      return;
+    }
+    DestLOI = *SrcLOI;
+  }
+
+  assert(DestLOI.KnownZero.getBitWidth() == BitWidth &&
+         DestLOI.KnownOne.getBitWidth() == BitWidth &&
+         "Masks should have the same bit width as the type.");
+
+  for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
+    Value *V = PN->getIncomingValue(i);
+    if (isa<UndefValue>(V) || isa<ConstantExpr>(V)) {
+      DestLOI.NumSignBits = 1;
+      APInt Zero(BitWidth, 0);
+      DestLOI.KnownZero = Zero;
+      DestLOI.KnownOne = Zero;
+      return;      
+    }
+
+    if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
+      APInt Val = CI->getValue().zextOrTrunc(BitWidth);
+      DestLOI.NumSignBits = std::min(DestLOI.NumSignBits, Val.getNumSignBits());
+      DestLOI.KnownZero &= ~Val;
+      DestLOI.KnownOne &= Val;
+      continue;
+    }
+
+    assert(ValueMap.count(V) && "V should have been placed in ValueMap when "
+                                "its CopyToReg node was created.");
+    unsigned SrcReg = ValueMap[V];
+    if (!TargetRegisterInfo::isVirtualRegister(SrcReg)) {
+      DestLOI.IsValid = false;
+      return;
+    }
+    const LiveOutInfo *SrcLOI = GetLiveOutRegInfo(SrcReg, BitWidth);
+    if (!SrcLOI) {
+      DestLOI.IsValid = false;
+      return;
+    }
+    DestLOI.NumSignBits = std::min(DestLOI.NumSignBits, SrcLOI->NumSignBits);
+    DestLOI.KnownZero &= SrcLOI->KnownZero;
+    DestLOI.KnownOne &= SrcLOI->KnownOne;
+  }
+}
+
 /// setByValArgumentFrameIndex - Record frame index for the byval
 /// argument. This overrides previous frame index entry for this argument,
 /// if any.

lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -842,7 +842,12 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
         }
       }
 
-      if (!AllPredsVisited) {
+      if (AllPredsVisited) {
+        for (BasicBlock::const_iterator I = LLVMBB->begin(), E = LLVMBB->end();
+             I != E && isa<PHINode>(I); ++I) {
+          FuncInfo->ComputePHILiveOutRegInfo(cast<PHINode>(I));
+        }
+      } else {
         for (BasicBlock::const_iterator I = LLVMBB->begin(), E = LLVMBB->end();
              I != E && isa<PHINode>(I); ++I) {
           FuncInfo->InvalidatePHILiveOutRegInfo(cast<PHINode>(I));

test/CodeGen/X86/phi-constants.ll

@@ -0,0 +1,35 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+
+%"class.std::bitset" = type { [8 x i8] }
+
+define zeroext i1 @_Z3fooPjmS_mRSt6bitsetILm32EE(i32* nocapture %a, i64 %asize, i32* nocapture %b, i64 %bsize, %"class.std::bitset"* %bits) nounwind readonly ssp noredzone {
+entry:
+  %tmp.i.i.i.i = bitcast %"class.std::bitset"* %bits to i64*
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %0 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+  %conv = zext i32 %0 to i64
+  %cmp = icmp eq i64 %conv, %bsize
+  br i1 %cmp, label %return, label %for.body
+
+for.body:                                         ; preds = %for.cond
+  %arrayidx = getelementptr inbounds i32* %b, i64 %conv
+  %tmp5 = load i32* %arrayidx, align 4
+  %conv6 = zext i32 %tmp5 to i64
+  %rem.i.i.i.i = and i64 %conv6, 63
+  %tmp3.i = load i64* %tmp.i.i.i.i, align 8
+  %shl.i.i = shl i64 1, %rem.i.i.i.i
+  %and.i = and i64 %shl.i.i, %tmp3.i
+  %cmp.i = icmp eq i64 %and.i, 0
+  br i1 %cmp.i, label %for.inc, label %return
+
+for.inc:                                          ; preds = %for.body
+  %inc = add i32 %0, 1
+  br label %for.cond
+
+return:                                           ; preds = %for.body, %for.cond
+; CHECK-NOT: and
+  %retval.0 = phi i1 [ true, %for.body ], [ false, %for.cond ]
+  ret i1 %retval.0
+}