Add support for computing "zext of value" in KnownBits. NFCI

Summary:
The description of KnownBits::zext() and
KnownBits::zextOrTrunc() has confusingly been telling
that the operation is equivalent to zero extending the
value we're tracking. That has not been true, instead
the user has been forced to explicitly set the extended
bits as known zero afterwards.

This patch adds a second argument to KnownBits::zext()
and KnownBits::zextOrTrunc() to control if the extended
bits should be considered as known zero or as unknown.

Reviewers: craig.topper, RKSimon

Reviewed By: RKSimon

Subscribers: javed.absar, hiraditya, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58650

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@355099 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Support/KnownBits.h b/include/llvm/Support/KnownBits.h
index 8983a06cf48a9bebe21401f1697a85111dc99ee3..66c2129fe797497cd655c06725a204c61ccc60e6 100644 (file)
--- a/include/llvm/Support/KnownBits.h
+++ b/include/llvm/Support/KnownBits.h
@@ -113,10 +113,16 @@ public:
     return KnownBits(Zero.trunc(BitWidth), One.trunc(BitWidth));
   }
 
-  /// Zero extends the underlying known Zero and One bits. This is equivalent
-  /// to zero extending the value we're tracking.
-  KnownBits zext(unsigned BitWidth) {
-    return KnownBits(Zero.zext(BitWidth), One.zext(BitWidth));
+  /// Extends the underlying known Zero and One bits.
+  /// By setting ExtendedBitsAreKnownZero=true this will be equivalent to
+  /// zero extending the value we're tracking.
+  /// With ExtendedBitsAreKnownZero=false the extended bits are set to unknown.
+  KnownBits zext(unsigned BitWidth, bool ExtendedBitsAreKnownZero) {
+    unsigned OldBitWidth = getBitWidth();
+    APInt NewZero = Zero.zext(BitWidth);
+    if (ExtendedBitsAreKnownZero)
+      NewZero.setBitsFrom(OldBitWidth);
+    return KnownBits(NewZero, One.zext(BitWidth));
   }
 
   /// Sign extends the underlying known Zero and One bits. This is equivalent
@@ -125,9 +131,13 @@ public:
     return KnownBits(Zero.sext(BitWidth), One.sext(BitWidth));
   }
 
-  /// Zero extends or truncates the underlying known Zero and One bits. This is
-  /// equivalent to zero extending or truncating the value we're tracking.
-  KnownBits zextOrTrunc(unsigned BitWidth) {
+  /// Extends or truncates the underlying known Zero and One bits. When
+  /// extending the extended bits can either be set as known zero (if
+  /// ExtendedBitsAreKnownZero=true) or as unknown (if
+  /// ExtendedBitsAreKnownZero=false).
+  KnownBits zextOrTrunc(unsigned BitWidth, bool ExtendedBitsAreKnownZero) {
+    if (BitWidth > getBitWidth())
+      return zext(BitWidth, ExtendedBitsAreKnownZero);
     return KnownBits(Zero.zextOrTrunc(BitWidth), One.zextOrTrunc(BitWidth));
   }
 

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 80a08e2fdd0217e095dc60006b025754fad5e9da..f6e3886f652e02512f299b197f2b56beccbf483b 100644 (file)
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -1128,12 +1128,9 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
       Q.DL.getTypeSizeInBits(ScalarTy);
 
     assert(SrcBitWidth && "SrcBitWidth can't be zero");
-    Known = Known.zextOrTrunc(SrcBitWidth);
+    Known = Known.zextOrTrunc(SrcBitWidth, false);
     computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
-    Known = Known.zextOrTrunc(BitWidth);
-    // Any top bits are known to be zero.
-    if (BitWidth > SrcBitWidth)
-      Known.Zero.setBitsFrom(SrcBitWidth);
+    Known = Known.zextOrTrunc(BitWidth, true /* ExtendedBitsAreKnownZero */);
     break;
   }
   case Instruction::BitCast: {

diff --git a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index 4a465e8e9ca220a379f5106595b5e7a809e4fc49..de4252aebdf248a27e366a772d2c0db96aff076c 100644 (file)
--- a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
@@ -400,7 +400,7 @@ FunctionLoweringInfo::GetLiveOutRegInfo(unsigned Reg, unsigned BitWidth) {
 
   if (BitWidth > LOI->Known.getBitWidth()) {
     LOI->NumSignBits = 1;
-    LOI->Known = LOI->Known.zextOrTrunc(BitWidth);
+    LOI->Known = LOI->Known.zext(BitWidth, false /* => any extend */);
   }
 
   return LOI;

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index c0bcb7ab1ff3561c7e466f23d2757ccf4a477902..3851fbb96ae7711f4fddeeef06ae9a6e77b4c9eb 100644 (file)
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2800,15 +2800,12 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
     EVT InVT = Op.getOperand(0).getValueType();
     APInt InDemandedElts = DemandedElts.zextOrSelf(InVT.getVectorNumElements());
     Known = computeKnownBits(Op.getOperand(0), InDemandedElts, Depth + 1);
-    Known = Known.zext(BitWidth);
-    Known.Zero.setBitsFrom(InVT.getScalarSizeInBits());
+    Known = Known.zext(BitWidth, true /* ExtendedBitsAreKnownZero */);
     break;
   }
   case ISD::ZERO_EXTEND: {
-    EVT InVT = Op.getOperand(0).getValueType();
     Known = computeKnownBits(Op.getOperand(0), DemandedElts, Depth + 1);
-    Known = Known.zext(BitWidth);
-    Known.Zero.setBitsFrom(InVT.getScalarSizeInBits());
+    Known = Known.zext(BitWidth, true /* ExtendedBitsAreKnownZero */);
     break;
   }
   case ISD::SIGN_EXTEND_VECTOR_INREG: {
@@ -2829,7 +2826,7 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
   }
   case ISD::ANY_EXTEND: {
     Known = computeKnownBits(Op.getOperand(0), Depth+1);
-    Known = Known.zext(BitWidth);
+    Known = Known.zext(BitWidth, false /* ExtendedBitsAreKnownZero */);
     break;
   }
   case ISD::TRUNCATE: {
@@ -3026,7 +3023,7 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
       Known = computeKnownBits(InVec, Depth + 1);
     }
     if (BitWidth > EltBitWidth)
-      Known = Known.zext(BitWidth);
+      Known = Known.zext(BitWidth, false /* => any extend */);
     break;
   }
   case ISD::INSERT_VECTOR_ELT: {

diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index b05e8f14b380746bf38b125984bbc89a6475d159..f9e853058ac9980db0bd7311b4dab6fffcf507eb 100644 (file)
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1163,8 +1163,8 @@ bool TargetLowering::SimplifyDemandedBits(
     if (SimplifyDemandedBits(Src, InDemandedBits, Known, TLO, Depth + 1))
       return true;
     assert(!Known.hasConflict() && "Bits known to be one AND zero?");
-    Known = Known.zext(BitWidth);
-    Known.Zero.setBitsFrom(InBits);
+    assert(Known.getBitWidth() == InBits && "Src width has changed?");
+    Known = Known.zext(BitWidth, true /* ExtendedBitsAreKnownZero */);
     break;
   }
   case ISD::SIGN_EXTEND: {
@@ -1217,7 +1217,7 @@ bool TargetLowering::SimplifyDemandedBits(
     if (SimplifyDemandedBits(Src, InDemandedBits, Known, TLO, Depth + 1))
       return true;
     assert(!Known.hasConflict() && "Bits known to be one AND zero?");
-    Known = Known.zext(BitWidth);
+    Known = Known.zext(BitWidth, false /* => any extend */);
     break;
   }
   case ISD::TRUNCATE: {
@@ -1312,7 +1312,7 @@ bool TargetLowering::SimplifyDemandedBits(
 
     Known = Known2;
     if (BitWidth > EltBitWidth)
-      Known = Known.zext(BitWidth);
+      Known = Known.zext(BitWidth, false /* => any extend */);
     break;
   }
   case ISD::BITCAST: {

diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 01ee6a33c7cc208c54de3e99be41571a42a637e4..524b84ec6f2f4d8c418bf6f746c70476dfbd23a0 100644 (file)
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -13706,8 +13706,7 @@ void ARMTargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
     if (Op.getOpcode() == ARMISD::VGETLANEs)
       Known = Known.sext(DstSz);
     else {
-      Known = Known.zext(DstSz);
-      Known.Zero.setBitsFrom(SrcSz);
+      Known = Known.zext(DstSz, true /* extended bits are known zero */);
     }
     assert(DstSz == Known.getBitWidth());
     break;

diff --git a/lib/Target/SystemZ/SystemZISelLowering.cpp b/lib/Target/SystemZ/SystemZISelLowering.cpp
index abb70e0c152b781719099e24dde8f45f6548cd89..e6cd53f9c4e07d4e4bf019ba696e35a389bf5bce 100644 (file)
--- a/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -6053,12 +6053,10 @@ SystemZTargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
     case Intrinsic::s390_vuplhw:
     case Intrinsic::s390_vuplf: {
       SDValue SrcOp = Op.getOperand(1);
-      unsigned SrcBitWidth = SrcOp.getScalarValueSizeInBits();
       APInt SrcDemE = getDemandedSrcElements(Op, DemandedElts, 0);
       Known = DAG.computeKnownBits(SrcOp, SrcDemE, Depth + 1);
       if (IsLogical) {
-        Known = Known.zext(BitWidth);
-        Known.Zero.setBitsFrom(SrcBitWidth);
+        Known = Known.zext(BitWidth, true);
       } else
         Known = Known.sext(BitWidth);
       break;
@@ -6087,7 +6085,7 @@ SystemZTargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
   // Known has the width of the source operand(s). Adjust if needed to match
   // the passed bitwidth.
   if (Known.getBitWidth() != BitWidth)
-    Known = Known.zextOrTrunc(BitWidth);
+    Known = Known.zextOrTrunc(BitWidth, false);
 }
 
 static unsigned computeNumSignBitsBinOp(SDValue Op, const APInt &DemandedElts,

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 4c85267343a7a0532735fd019f7f122eac5e4a9b..9b585846fa07647df62ae00e020a9c2e0a8244a3 100644 (file)
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -30412,7 +30412,7 @@ void X86TargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
     APInt DemandedElt = APInt::getOneBitSet(SrcVT.getVectorNumElements(),
                                             Op.getConstantOperandVal(1));
     Known = DAG.computeKnownBits(Src, DemandedElt, Depth + 1);
-    Known = Known.zextOrTrunc(BitWidth);
+    Known = Known.zextOrTrunc(BitWidth, false);
     Known.Zero.setBitsFrom(SrcVT.getScalarSizeInBits());
     break;
   }

diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 19cdea6923045418f1ca028326875e93ba163c67..6f9aadea55dcf9439af629694836d12651708cfe 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -365,10 +365,9 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     KnownBits InputKnown(SrcBitWidth);
     if (SimplifyDemandedBits(I, 0, InputDemandedMask, InputKnown, Depth + 1))
       return I;
-    Known = InputKnown.zextOrTrunc(BitWidth);
-    // Any top bits are known to be zero.
-    if (BitWidth > SrcBitWidth)
-      Known.Zero.setBitsFrom(SrcBitWidth);
+    assert(InputKnown.getBitWidth() == SrcBitWidth && "Src width changed?");
+    Known = InputKnown.zextOrTrunc(BitWidth,
+                                   true /* ExtendedBitsAreKnownZero */);
     assert(!Known.hasConflict() && "Bits known to be one AND zero?");
     break;
   }