[mlir] Execute same operand name constraints before user constraints. (#162526)

For a pattern like this:

    Pat<(MyOp $x, $x),
        (...),
        [(MyCheck $x)]>;

The old implementation generates:

    Pat<(MyOp $x0, $x1),
        (...),
        [(MyCheck $x0),
         ($x0 == $x1)]>;

This is not very straightforward, because the $x name appears in the
source pattern; it's attempting to assume equality check will be
performed as part of the source pattern matching.

This commit moves the equality checks before the other constraints,
i.e.:

    Pat<(MyOp $x0, $x1),
        (...),
        [($x0 == $x1),
         (MyCheck $x0)]>;

Author: wecing

mlir/tools/mlir-tblgen/RewriterGen.cpp

@@ -1024,6 +1024,32 @@ void PatternEmitter::emitMatchLogic(DagNode tree, StringRef opName) {
   int depth = 0;
   emitMatch(tree, opName, depth);
 
+  // Some of the operands could be bound to the same symbol name, we need
+  // to enforce equality constraint on those.
+  // This has to happen before user provided constraints, which may assume the
+  // same name checks are already performed, since in the pattern source code
+  // the user provided constraints appear later.
+  // TODO: we should be able to emit equality checks early
+  // and short circuit unnecessary work if vars are not equal.
+  for (auto symbolInfoIt = symbolInfoMap.begin();
+       symbolInfoIt != symbolInfoMap.end();) {
+    auto range = symbolInfoMap.getRangeOfEqualElements(symbolInfoIt->first);
+    auto startRange = range.first;
+    auto endRange = range.second;
+
+    auto firstOperand = symbolInfoIt->second.getVarName(symbolInfoIt->first);
+    for (++startRange; startRange != endRange; ++startRange) {
+      auto secondOperand = startRange->second.getVarName(symbolInfoIt->first);
+      emitMatchCheck(
+          opName,
+          formatv("*{0}.begin() == *{1}.begin()", firstOperand, secondOperand),
+          formatv("\"Operands '{0}' and '{1}' must be equal\"", firstOperand,
+                  secondOperand));
+    }
+
+    symbolInfoIt = endRange;
+  }
+
   for (auto &appliedConstraint : pattern.getConstraints()) {
     auto &constraint = appliedConstraint.constraint;
     auto &entities = appliedConstraint.entities;
@@ -1068,29 +1094,6 @@ void PatternEmitter::emitMatchLogic(DagNode tree, StringRef opName) {
     }
   }
 
-  // Some of the operands could be bound to the same symbol name, we need
-  // to enforce equality constraint on those.
-  // TODO: we should be able to emit equality checks early
-  // and short circuit unnecessary work if vars are not equal.
-  for (auto symbolInfoIt = symbolInfoMap.begin();
-       symbolInfoIt != symbolInfoMap.end();) {
-    auto range = symbolInfoMap.getRangeOfEqualElements(symbolInfoIt->first);
-    auto startRange = range.first;
-    auto endRange = range.second;
-
-    auto firstOperand = symbolInfoIt->second.getVarName(symbolInfoIt->first);
-    for (++startRange; startRange != endRange; ++startRange) {
-      auto secondOperand = startRange->second.getVarName(symbolInfoIt->first);
-      emitMatchCheck(
-          opName,
-          formatv("*{0}.begin() == *{1}.begin()", firstOperand, secondOperand),
-          formatv("\"Operands '{0}' and '{1}' must be equal\"", firstOperand,
-                  secondOperand));
-    }
-
-    symbolInfoIt = endRange;
-  }
-
   LLVM_DEBUG(llvm::dbgs() << "--- done emitting match logic ---\n");
 }