[PATCH] D60952: [ConstantRange] Add urem support

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
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Herald added subscribers: llvm-commits, hiraditya.
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Add urem support to ConstantRange, so we can handle in in LVI. This is an approximate implementation that tries to capture the most useful conditions: If the LHS is always strictly smaller than the RHS, then the urem is a no-op and the result is the same as the LHS range. Otherwise the lower bound is zero and the upper bound is min(LHSMax, RHSMax - 1).


Repository:
  rL LLVM

https://reviews.llvm.org/D60952

Files:
  llvm/include/llvm/IR/ConstantRange.h
  llvm/lib/IR/ConstantRange.cpp
  llvm/unittests/IR/ConstantRangeTest.cpp


Index: llvm/unittests/IR/ConstantRangeTest.cpp
===================================================================
--- llvm/unittests/IR/ConstantRangeTest.cpp
+++ llvm/unittests/IR/ConstantRangeTest.cpp
@@ -759,6 +759,33 @@
   EXPECT_EQ(Wrap.udiv(Wrap), Full);
 }
 
+TEST_F(ConstantRangeTest, URem) {
+  EXPECT_EQ(Full.urem(Empty), Empty);
+  EXPECT_EQ(Empty.urem(Full), Empty);
+  // urem by zero is poison.
+  EXPECT_EQ(Full.urem(ConstantRange(APInt(16, 0))), Empty);
+  // urem by full range doesn't contain MaxValue.
+  EXPECT_EQ(Full.urem(Full), ConstantRange(APInt(16, 0), APInt(16, 0xffff)));
+  // urem is upper bounded by maximum RHS minus one.
+  EXPECT_EQ(Full.urem(ConstantRange(APInt(16, 0), APInt(16, 123))),
+            ConstantRange(APInt(16, 0), APInt(16, 122)));
+  // urem is upper bounded by maximum LHS.
+  EXPECT_EQ(ConstantRange(APInt(16, 0), APInt(16, 123)).urem(Full),
+            ConstantRange(APInt(16, 0), APInt(16, 123)));
+  // If the LHS is always lower than the RHS, the result is the LHS.
+  EXPECT_EQ(ConstantRange(APInt(16, 10), APInt(16, 20))
+                .urem(ConstantRange(APInt(16, 20), APInt(16, 30))),
+            ConstantRange(APInt(16, 10), APInt(16, 20)));
+  // It has to be strictly lower, otherwise the top value may wrap to zero.
+  EXPECT_EQ(ConstantRange(APInt(16, 10), APInt(16, 20))
+                .urem(ConstantRange(APInt(16, 19), APInt(16, 30))),
+            ConstantRange(APInt(16, 0), APInt(16, 20)));
+  // [12, 14] % 10 is [2, 4], but we conservatively compute [0, 9].
+  EXPECT_EQ(ConstantRange(APInt(16, 12), APInt(16, 15))
+                .urem(ConstantRange(APInt(16, 10))),
+            ConstantRange(APInt(16, 0), APInt(16, 10)));
+}
+
 TEST_F(ConstantRangeTest, Shl) {
   ConstantRange Some2(APInt(16, 0xfff), APInt(16, 0x8000));
   ConstantRange WrapNullMax(APInt(16, 0x1), APInt(16, 0x0));
Index: llvm/lib/IR/ConstantRange.cpp
===================================================================
--- llvm/lib/IR/ConstantRange.cpp
+++ llvm/lib/IR/ConstantRange.cpp
@@ -794,6 +794,8 @@
     return multiply(Other);
   case Instruction::UDiv:
     return udiv(Other);
+  case Instruction::URem:
+    return urem(Other);
   case Instruction::Shl:
     return shl(Other);
   case Instruction::LShr:
@@ -991,6 +993,18 @@
   return getNonEmpty(std::move(Lower), std::move(Upper));
 }
 
+ConstantRange ConstantRange::urem(const ConstantRange &RHS) const {
+  if (isEmptySet() || RHS.isEmptySet() || RHS.getUnsignedMax().isNullValue())
+    return getEmpty();
+
+  // L % R for L < R is L.
+  APInt Lower = getUnsignedMax().ult(RHS.getUnsignedMin())
+      ? getUnsignedMin() : APInt::getNullValue(getBitWidth());
+  // L % R is <= L and < R.
+  APInt Upper = APIntOps::umin(getUnsignedMax(), RHS.getUnsignedMax() - 1) + 1;
+  return getNonEmpty(std::move(Lower), std::move(Upper));
+}
+
 ConstantRange
 ConstantRange::binaryAnd(const ConstantRange &Other) const {
   if (isEmptySet() || Other.isEmptySet())
Index: llvm/include/llvm/IR/ConstantRange.h
===================================================================
--- llvm/include/llvm/IR/ConstantRange.h
+++ llvm/include/llvm/IR/ConstantRange.h
@@ -356,6 +356,11 @@
   /// \p Other.
   ConstantRange udiv(const ConstantRange &Other) const;
 
+  /// Return a new range representing the possible values resulting
+  /// from an unsigned remainder operation of a value in this range and a
+  /// value in \p Other.
+  ConstantRange urem(const ConstantRange &Other) const;
+
   /// Return a new range representing the possible values resulting
   /// from a binary-and of a value in this range by a value in \p Other.
   ConstantRange binaryAnd(const ConstantRange &Other) const;


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