[llvm] [InstCombine] Fold comparison of adding two z/sext booleans (PR #67895)

[Nikita Popov via llvm-commits]

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@@ -2895,19 +2896,89 @@ Instruction *InstCombinerImpl::foldICmpSubConstant(ICmpInst &Cmp,
   return new ICmpInst(SwappedPred, Add, ConstantInt::get(Ty, ~C));
 }
 
+static Value *createLogicFromTable(const std::bitset<4> &Table, Value *Op0,
+                                   Value *Op1, IRBuilderBase &Builder,
+                                   bool HasOneUse) {
+  switch (Table.to_ulong()) {
+  case 0: // 0 0 0 0
+    return Builder.getFalse();
+  case 1: // 0 0 0 1
+    return HasOneUse ? Builder.CreateNot(Builder.CreateOr(Op0, Op1)) : nullptr;
+  case 2: // 0 0 1 0
+    return HasOneUse ? Builder.CreateAnd(Builder.CreateNot(Op0), Op1) : nullptr;
+  case 3: // 0 0 1 1
+    return Builder.CreateNot(Op0);
+  case 4: // 0 1 0 0
+    return HasOneUse ? Builder.CreateAnd(Op0, Builder.CreateNot(Op1)) : nullptr;
+  case 5: // 0 1 0 1
+    return Builder.CreateNot(Op1);
+  case 6: // 0 1 1 0
+    return Builder.CreateXor(Op0, Op1);
+  case 7: // 0 1 1 1
+    return HasOneUse ? Builder.CreateNot(Builder.CreateAnd(Op0, Op1)) : nullptr;
+  case 8: // 1 0 0 0
+    return Builder.CreateAnd(Op0, Op1);
+  case 9: // 1 0 0 1
+    return HasOneUse ? Builder.CreateNot(Builder.CreateXor(Op0, Op1)) : nullptr;
+  case 10: // 1 0 1 0
+    return Op1;
+  case 11: // 1 0 1 1
+    return HasOneUse ? Builder.CreateOr(Builder.CreateNot(Op0), Op1) : nullptr;
+  case 12: // 1 1 0 0
+    return Op0;
+  case 13: // 1 1 0 1
+    return HasOneUse ? Builder.CreateOr(Op0, Builder.CreateNot(Op1)) : nullptr;
+  case 14: // 1 1 1 0
+    return Builder.CreateOr(Op0, Op1);
+  case 15: // 1 1 1 1
+    return Builder.getTrue();
+  default:
+    llvm_unreachable("Invalid Operation");
+  }
+  return nullptr;
+}
+
 /// Fold icmp (add X, Y), C.
 Instruction *InstCombinerImpl::foldICmpAddConstant(ICmpInst &Cmp,
                                                    BinaryOperator *Add,
                                                    const APInt &C) {
   Value *Y = Add->getOperand(1);
+  Value *X = Add->getOperand(0);
+
+  Value *Op0, *Op1;
+  Instruction *Ext0, *Ext1;
+  const CmpInst::Predicate Pred = Cmp.getPredicate();
+  if (match(Add, m_Add(m_CombineAnd(m_Instruction(Ext0),
+                                    m_OneUse(m_ZExtOrSExt(m_Value(Op0)))),
+                       m_CombineAnd(m_Instruction(Ext1),
+                                    m_OneUse(m_ZExtOrSExt(m_Value(Op1)))))) &&
----------------
nikic wrote:

I believe these m_OneUse's can be dropped. The one-use handling on the add is sufficient.

We should have a test where there are extra uses of both exts, but not of the add.

https://github.com/llvm/llvm-project/pull/67895