[KnownBits] Move ValueTracking/SelectionDAG UDIV KnownBits handling t…

…o KnownBits::udiv. NFCI. Both these have the same implementation - so move them to a single KnownBits copy. GlobalISel will be able to use this as well with minimal effort.
llvm · Nov 5, 2020 · 32bee18 · 32bee18
1 parent 2f84b59
commit 32bee18
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Showing 5 changed files with 36 additions and 23 deletions.
diff --git a/llvm/include/llvm/Support/KnownBits.h b/llvm/include/llvm/Support/KnownBits.h
@@ -258,6 +258,9 @@ struct KnownBits {
   /// Compute known bits resulting from multiplying LHS and RHS.
   static KnownBits computeForMul(const KnownBits &LHS, const KnownBits &RHS);
 
+  /// Compute known bits for udiv(LHS, RHS).
+  static KnownBits udiv(const KnownBits &LHS, const KnownBits &RHS);
+
   /// Compute known bits for umax(LHS, RHS).
   static KnownBits umax(const KnownBits &LHS, const KnownBits &RHS);
 

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1127,19 +1127,9 @@ static void computeKnownBitsFromOperator(const Operator *I,
     break;
   }
   case Instruction::UDiv: {
-    // For the purposes of computing leading zeros we can conservatively
-    // treat a udiv as a logical right shift by the power of 2 known to
-    // be less than the denominator.
-    computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
-    unsigned LeadZ = Known2.countMinLeadingZeros();
-
-    Known2.resetAll();
+    computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
     computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
-    unsigned RHSMaxLeadingZeros = Known2.countMaxLeadingZeros();
-    if (RHSMaxLeadingZeros != BitWidth)
-      LeadZ = std::min(BitWidth, LeadZ + BitWidth - RHSMaxLeadingZeros - 1);
-
-    Known.Zero.setHighBits(LeadZ);
+    Known = KnownBits::udiv(Known, Known2);
     break;
   }
   case Instruction::Select: {

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2884,18 +2884,9 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
     break;
   }
   case ISD::UDIV: {
-    // For the purposes of computing leading zeros we can conservatively
-    // treat a udiv as a logical right shift by the power of 2 known to
-    // be less than the denominator.
-    Known2 = computeKnownBits(Op.getOperand(0), DemandedElts, Depth + 1);
-    unsigned LeadZ = Known2.countMinLeadingZeros();
-
+    Known = computeKnownBits(Op.getOperand(0), DemandedElts, Depth + 1);
     Known2 = computeKnownBits(Op.getOperand(1), DemandedElts, Depth + 1);
-    unsigned RHSMaxLeadingZeros = Known2.countMaxLeadingZeros();
-    if (RHSMaxLeadingZeros != BitWidth)
-      LeadZ = std::min(BitWidth, LeadZ + BitWidth - RHSMaxLeadingZeros - 1);
-
-    Known.Zero.setHighBits(LeadZ);
+    Known = KnownBits::udiv(Known, Known2);
     break;
   }
   case ISD::SELECT:

diff --git a/llvm/lib/Support/KnownBits.cpp b/llvm/lib/Support/KnownBits.cpp
@@ -306,6 +306,24 @@ KnownBits KnownBits::computeForMul(const KnownBits &LHS, const KnownBits &RHS) {
   return Res;
 }
 
+KnownBits KnownBits::udiv(const KnownBits &LHS, const KnownBits &RHS) {
+  unsigned BitWidth = LHS.getBitWidth();
+  assert(!LHS.hasConflict() && !RHS.hasConflict());
+  KnownBits Known(BitWidth);
+
+  // For the purposes of computing leading zeros we can conservatively
+  // treat a udiv as a logical right shift by the power of 2 known to
+  // be less than the denominator.
+  unsigned LeadZ = LHS.countMinLeadingZeros();
+  unsigned RHSMaxLeadingZeros = RHS.countMaxLeadingZeros();
+
+  if (RHSMaxLeadingZeros != BitWidth)
+    LeadZ = std::min(BitWidth, LeadZ + BitWidth - RHSMaxLeadingZeros - 1);
+
+  Known.Zero.setHighBits(LeadZ);
+  return Known;
+}
+
 KnownBits &KnownBits::operator&=(const KnownBits &RHS) {
   // Result bit is 0 if either operand bit is 0.
   Zero |= RHS.Zero;

diff --git a/llvm/unittests/Support/KnownBitsTest.cpp b/llvm/unittests/Support/KnownBitsTest.cpp
@@ -113,6 +113,7 @@ TEST(KnownBitsTest, BinaryExhaustive) {
       KnownBits KnownSMax(KnownAnd);
       KnownBits KnownSMin(KnownAnd);
       KnownBits KnownMul(KnownAnd);
+      KnownBits KnownUDiv(KnownAnd);
       KnownBits KnownShl(KnownAnd);
       KnownBits KnownLShr(KnownAnd);
       KnownBits KnownAShr(KnownAnd);
@@ -153,6 +154,12 @@ TEST(KnownBitsTest, BinaryExhaustive) {
           KnownMul.One &= Res;
           KnownMul.Zero &= ~Res;
 
+          if (!N2.isNullValue()) {
+            Res = N1.udiv(N2);
+            KnownUDiv.One &= Res;
+            KnownUDiv.Zero &= ~Res;
+          }
+
           if (N2.ult(1ULL << N1.getBitWidth())) {
             Res = N1.shl(N2);
             KnownShl.One &= Res;
@@ -207,6 +214,10 @@ TEST(KnownBitsTest, BinaryExhaustive) {
       EXPECT_TRUE(ComputedMul.Zero.isSubsetOf(KnownMul.Zero));
       EXPECT_TRUE(ComputedMul.One.isSubsetOf(KnownMul.One));
 
+      KnownBits ComputedUDiv = KnownBits::udiv(Known1, Known2);
+      EXPECT_TRUE(ComputedUDiv.Zero.isSubsetOf(KnownUDiv.Zero));
+      EXPECT_TRUE(ComputedUDiv.One.isSubsetOf(KnownUDiv.One));
+
       KnownBits ComputedShl = KnownBits::shl(Known1, Known2);
       EXPECT_TRUE(ComputedShl.Zero.isSubsetOf(KnownShl.Zero));
       EXPECT_TRUE(ComputedShl.One.isSubsetOf(KnownShl.One));