[Mlir-commits] [mlir] [mlir][emitc] Add a structured for operation (PR #68206)

[Simon Camphausen]

================
@@ -37,6 +37,106 @@ struct SCFToEmitCPass : public impl::SCFToEmitCBase<SCFToEmitCPass> {
   void runOnOperation() override;
 };
 
+// Lower scf::for to emitc::for, implementing return values using
+// emitc::variable's updated within loop body.
+struct ForLowering : public OpRewritePattern<ForOp> {
+  using OpRewritePattern<ForOp>::OpRewritePattern;
+
+  LogicalResult matchAndRewrite(ForOp forOp,
+                                PatternRewriter &rewriter) const override;
+};
+
+// Create an uninitialized emitc::variable op for each result of given op.
+template <typename T>
+static SmallVector<Value> createVariablesForResults(T op,
+                                                    PatternRewriter &rewriter) {
+  SmallVector<Value> resultVariables;
+
+  if (!op.getNumResults())
+    return resultVariables;
+
+  Location loc = op->getLoc();
+  MLIRContext *context = op.getContext();
+
+  auto insertionPoint = rewriter.saveInsertionPoint();
+  rewriter.setInsertionPoint(op);
+
+  for (OpResult result : op.getResults()) {
+    Type resultType = result.getType();
+    auto noInit = emitc::OpaqueAttr::get(context, "");
+    auto var = rewriter.create<emitc::VariableOp>(loc, resultType, noInit);
+    resultVariables.push_back(var);
+  }
+
+  rewriter.restoreInsertionPoint(insertionPoint);
+
+  return resultVariables;
+}
+
+// Create a series of assign ops assigning given values to given variables at
+// the current insertion point of given rewriter.
+static void assignValues(ValueRange values, SmallVector<Value> &variables,
+                         PatternRewriter &rewriter, Location loc) {
+  for (auto value2Var : llvm::zip(values, variables)) {
+    Value value = std::get<0>(value2Var);
+    Value var = std::get<1>(value2Var);
----------------
simon-camp wrote:

```suggestion
  for (auto [value, var] : llvm::zip(values, variables)) {
```
or
```suggestion
  for (auto it : llvm::zip(values, variables)) {
    Value value = std::get<0>(it);
    Value var = std::get<1>(it);
```
Not sure what the recommended style is. Using a tuple is used about twice as often as structured bindings in the codebase.


https://github.com/llvm/llvm-project/pull/68206