[Comb] Truth table operation

include/circt/Dialect/Comb/Combinational.td

@@ -286,3 +286,33 @@ def MuxOp : CombOp<"mux",
   let hasFolder = true;
   let hasCanonicalizer = true;
 }
+
+def TruthTableOp : CombOp<"truth_table", [Pure]> {
+  let summary = "Return a true/false based on a lookup table";
+  let description = [{
+    ```
+      %a = ... : i1
+      %b = ... : i1
+      %0 = comb.truth_table %a, %b -> [false, true, true, false]
+    ```
+
+    This operation assumes a fully elaborated table -- 2^n entries. Inputs are
+    sorted MSB -> LSB from left to right and the offset into `lookupTable` is
+    computed from them. The table is sorted from 0 -> (2^n - 1) from left to
+    right.
+
+    No difference from array_get into an array of constants except for xprop
+    behavior. If one of the inputs is unknown, but said input doesn't make a
+    difference in the output (based on the lookup table) the result should not
+    be 'x' -- it should be the well-known result.
+  }];
+
+  let arguments = (ins Variadic<I1>:$inputs, BoolArrayAttr:$lookupTable);
+  let results = (outs I1:$result);
+
+  let assemblyFormat = [{
+    $inputs `->` $lookupTable attr-dict
+  }];
+
+  let hasVerifier = 1;
+}

lib/Dialect/Comb/CombOps.cpp

@@ -282,6 +282,18 @@ LogicalResult ExtractOp::verify() {
   return success();
 }
 
+LogicalResult TruthTableOp::verify() {
+  size_t numInputs = getInputs().size();
+  if (numInputs >= sizeof(size_t) * 8)
+    return emitOpError("Truth tables support a maximum of ")
+           << sizeof(size_t) * 8 - 1 << " inputs on your platform";
+
+  ArrayAttr table = getLookupTable();
+  if (table.size() != (1ull << numInputs))
+    return emitOpError("Expected lookup table of 2^n length");
+  return success();
+}
+
 //===----------------------------------------------------------------------===//
 // TableGen generated logic.
 //===----------------------------------------------------------------------===//

test/Dialect/Comb/errors.mlir

@@ -0,0 +1,13 @@
+// RUN: circt-opt %s -split-input-file -verify-diagnostics
+
+hw.module @err(%a: i1, %b: i1) -> () {
+  // expected-error @+1 {{Expected lookup table of 2^n length}}
+  %0 = comb.truth_table %a, %b -> [true, false]
+}
+
+// -----
+
+hw.module @err(%a: i1, %b: i1) -> () {
+  // expected-error @+1 {{Truth tables support a maximum of 63 inputs}}
+  %0 = comb.truth_table %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b, %a, %b -> [false]
+}