[llvm] 6729b6d - [KnownBits] Move ValueTracking SREM KnownBits handling to KnownBits::srem. NFCI.

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-11-05T14:58:33Z
New Revision: 6729b6de1f5b753251b4f31fd6349912d07d34ef

URL: https://github.com/llvm/llvm-project/commit/6729b6de1f5b753251b4f31fd6349912d07d34ef
DIFF: https://github.com/llvm/llvm-project/commit/6729b6de1f5b753251b4f31fd6349912d07d34ef.diff

LOG: [KnownBits] Move ValueTracking SREM KnownBits handling to KnownBits::srem. NFCI.

Move the ValueTracking implementation to KnownBits, the SelectionDAG version is more limited so I'm intending to replace that as a separate commit.

Added: 
    

Modified: 
    llvm/include/llvm/Support/KnownBits.h
    llvm/lib/Analysis/ValueTracking.cpp
    llvm/lib/Support/KnownBits.cpp
    llvm/unittests/Support/KnownBitsTest.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/Support/KnownBits.h b/llvm/include/llvm/Support/KnownBits.h
index 2ef4a8f38c20..de1c0cdf9177 100644
--- a/llvm/include/llvm/Support/KnownBits.h
+++ b/llvm/include/llvm/Support/KnownBits.h
@@ -264,6 +264,9 @@ struct KnownBits {
   /// Compute known bits for urem(LHS, RHS).
   static KnownBits urem(const KnownBits &LHS, const KnownBits &RHS);
 
+  /// Compute known bits for srem(LHS, RHS).
+  static KnownBits srem(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
index 632a5eaef4b2..44cf4f80b59d 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1294,39 +1294,11 @@ static void computeKnownBitsFromOperator(const Operator *I,
     break;
   }
   case Instruction::SRem:
-    if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
-      APInt RA = Rem->getValue().abs();
-      if (RA.isPowerOf2()) {
-        APInt LowBits = RA - 1;
-        computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
-
-        // The low bits of the first operand are unchanged by the srem.
-        Known.Zero = Known2.Zero & LowBits;
-        Known.One = Known2.One & LowBits;
-
-        // If the first operand is non-negative or has all low bits zero, then
-        // the upper bits are all zero.
-        if (Known2.isNonNegative() || LowBits.isSubsetOf(Known2.Zero))
-          Known.Zero |= ~LowBits;
-
-        // If the first operand is negative and not all low bits are zero, then
-        // the upper bits are all one.
-        if (Known2.isNegative() && LowBits.intersects(Known2.One))
-          Known.One |= ~LowBits;
-
-        assert((Known.Zero & Known.One) == 0 && "Bits known to be one AND zero?");
-        break;
-      }
-    }
-
-    // The sign bit is the LHS's sign bit, except when the result of the
-    // remainder is zero.
-    computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
-    // If it's known zero, our sign bit is also zero.
-    if (Known2.isNonNegative())
-      Known.makeNonNegative();
-
+    computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
+    computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
+    Known = KnownBits::srem(Known, Known2);
     break;
+
   case Instruction::URem:
     computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
     computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);

diff  --git a/llvm/lib/Support/KnownBits.cpp b/llvm/lib/Support/KnownBits.cpp
index 3a509382a1f4..7ca949b418bf 100644
--- a/llvm/lib/Support/KnownBits.cpp
+++ b/llvm/lib/Support/KnownBits.cpp
@@ -345,6 +345,36 @@ KnownBits KnownBits::urem(const KnownBits &LHS, const KnownBits &RHS) {
   return Known;
 }
 
+KnownBits KnownBits::srem(const KnownBits &LHS, const KnownBits &RHS) {
+  unsigned BitWidth = LHS.getBitWidth();
+  assert(!LHS.hasConflict() && !RHS.hasConflict());
+  KnownBits Known(BitWidth);
+
+  if (RHS.isConstant() && RHS.getConstant().isPowerOf2()) {
+    // The low bits of the first operand are unchanged by the srem.
+    APInt LowBits = RHS.getConstant() - 1;
+    Known.Zero = LHS.Zero & LowBits;
+    Known.One = LHS.One & LowBits;
+
+    // If the first operand is non-negative or has all low bits zero, then
+    // the upper bits are all zero.
+    if (LHS.isNonNegative() || LowBits.isSubsetOf(LHS.Zero))
+      Known.Zero |= ~LowBits;
+
+    // If the first operand is negative and not all low bits are zero, then
+    // the upper bits are all one.
+    if (LHS.isNegative() && LowBits.intersects(LHS.One))
+      Known.One |= ~LowBits;
+    return Known;
+  }
+
+  // The sign bit is the LHS's sign bit, except when the result of the
+  // remainder is zero. If it's known zero, our sign bit is also zero.
+  if (LHS.isNonNegative())
+    Known.makeNonNegative();
+  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
index 60e61b5ce1a4..709a3fcb40c7 100644
--- a/llvm/unittests/Support/KnownBitsTest.cpp
+++ b/llvm/unittests/Support/KnownBitsTest.cpp
@@ -115,6 +115,7 @@ TEST(KnownBitsTest, BinaryExhaustive) {
       KnownBits KnownMul(KnownAnd);
       KnownBits KnownUDiv(KnownAnd);
       KnownBits KnownURem(KnownAnd);
+      KnownBits KnownSRem(KnownAnd);
       KnownBits KnownShl(KnownAnd);
       KnownBits KnownLShr(KnownAnd);
       KnownBits KnownAShr(KnownAnd);
@@ -163,6 +164,10 @@ TEST(KnownBitsTest, BinaryExhaustive) {
             Res = N1.urem(N2);
             KnownURem.One &= Res;
             KnownURem.Zero &= ~Res;
+
+            Res = N1.srem(N2);
+            KnownSRem.One &= Res;
+            KnownSRem.Zero &= ~Res;
           }
 
           if (N2.ult(1ULL << N1.getBitWidth())) {
@@ -227,6 +232,10 @@ TEST(KnownBitsTest, BinaryExhaustive) {
       EXPECT_TRUE(ComputedURem.Zero.isSubsetOf(KnownURem.Zero));
       EXPECT_TRUE(ComputedURem.One.isSubsetOf(KnownURem.One));
 
+      KnownBits ComputedSRem = KnownBits::srem(Known1, Known2);
+      EXPECT_TRUE(ComputedSRem.Zero.isSubsetOf(KnownSRem.Zero));
+      EXPECT_TRUE(ComputedSRem.One.isSubsetOf(KnownSRem.One));
+
       KnownBits ComputedShl = KnownBits::shl(Known1, Known2);
       EXPECT_TRUE(ComputedShl.Zero.isSubsetOf(KnownShl.Zero));
       EXPECT_TRUE(ComputedShl.One.isSubsetOf(KnownShl.One));