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

[Nikita Popov via llvm-commits]

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@@ -2895,19 +2896,86 @@ 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) {
+  switch (Table.to_ulong()) {
+    case 0: // 0 0 0 0
+      return Builder.getFalse();
+    case 1: // 0 0 0 1
+      return Builder.CreateNot(Builder.CreateOr(Op0, Op1));
+    case 2: // 0 0 1 0
+      return Builder.CreateAnd(Builder.CreateNot(Op0), Op1);
+    case 3: // 0 0 1 1
+      return Op1;
+    case 4: // 0 1 0 0
+      return Builder.CreateAnd(Op0, Builder.CreateNot(Op1));
+    case 5: // 0 1 0 1
+      return Op0;
+    case 6: // 0 1 1 0
+      return Builder.CreateXor(Op0, Op1);
+    case 7: // 0 1 1 1
+      return Builder.CreateNot(Builder.CreateAnd(Op0, Op1));
+    case 8: // 1 0 0 0
+      return Builder.CreateAnd(Op0, Op1);
+    case 9: // 1 0 0 1
+      return Builder.CreateNot(Builder.CreateXor(Op0, Op1));
+    case 10: // 1 0 1 0
+      return Builder.CreateNot(Op1);
+    case 11: // 1 0 1 1
+      return Builder.CreateOr(Builder.CreateNot(Op0), Op1);
+    case 12: // 1 1 0 0
+      return Builder.CreateNot(Op1);
+    case 13: // 1 1 0 1
+      return Builder.CreateOr(Op0, Builder.CreateNot(Op1));
+    case 14: // 1 1 1 0
+      return Builder.CreateOr(Op0, Op1);
+    case 15: // 1 1 1 1
+      return Builder.getTrue();
+  }
+  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_c_Add(m_CombineAnd(m_Instruction(Ext0),
----------------
nikic wrote:

m_c_Add -> m_Add

Also, we are missing a one-use check on the add itself. The one-use checks on the extensions are pointless if the add itself is multi-use.

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