[Mlir-commits] [mlir] [mlir][emitc] Add op modelling C expressions (PR #71631)

[Simon Camphausen]

================
@@ -0,0 +1,117 @@
+//===- Transforms.cpp - Patterns and transforms for the EmitC dialect------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Dialect/EmitC/Transforms/Transforms.h"
+#include "mlir/Dialect/EmitC/IR/EmitC.h"
+#include "mlir/IR/IRMapping.h"
+#include "mlir/IR/PatternMatch.h"
+#include "llvm/Support/Debug.h"
+
+namespace mlir {
+namespace emitc {
+
+ExpressionOp createExpression(Operation *op, OpBuilder &builder) {
+  assert(ExpressionOp::isCExpression(*op) && "Expected a C expression");
+
+  // Create an expression yielding the value returned by op.
+  assert(op->getNumResults() == 1 && "Expected exactly one result");
+  Value result = op->getResult(0);
+  Type resultType = result.getType();
+  Location loc = op->getLoc();
+
+  builder.setInsertionPointAfter(op);
+  auto expressionOp = builder.create<emitc::ExpressionOp>(loc, resultType);
+
+  // Replace all op's uses with the new expression's result.
+  result.replaceAllUsesWith(expressionOp.getResult());
+
+  // Create an op to yield op's value.
+  Region &region = expressionOp.getRegion();
+  Block &block = region.emplaceBlock();
+  builder.setInsertionPointToEnd(&block);
+  auto yieldOp = builder.create<emitc::YieldOp>(loc, result);
+
+  // Move op into the new expression.
+  op->moveBefore(yieldOp);
+
+  return expressionOp;
+}
+
+} // namespace emitc
+} // namespace mlir
+
+using namespace mlir;
+using namespace mlir::emitc;
+
+namespace {
+
+struct FoldExpressionOp : public OpRewritePattern<ExpressionOp> {
+  using OpRewritePattern<ExpressionOp>::OpRewritePattern;
+  LogicalResult matchAndRewrite(ExpressionOp expressionOp,
+                                PatternRewriter &rewriter) const override {
+    bool anythingFolded = false;
+    for (Operation &op : llvm::make_early_inc_range(
+             expressionOp.getBody()->without_terminator())) {
+      // Don't fold expressions whose result value has its address taken.
+      auto applyOp = dyn_cast<emitc::ApplyOp>(op);
+      if (applyOp && applyOp.getApplicableOperator() == "&")
+        continue;
+
+      for (Value operand : op.getOperands()) {
+        auto usedExpression =
+            dyn_cast_or_null<ExpressionOp>(operand.getDefiningOp());
+
+        if (!usedExpression)
+          continue;
+
+        // Don't fold expressions with multiple users: assume any
+        // re-materialization was done separately.
+        if (!usedExpression.getResult().hasOneUse())
+          continue;
+
+        // Don't fold expressions with side effects.
+        if (usedExpression.hasSideEffects())
+          continue;
+
+        // Fold the used expression into this expression by cloning all
+        // instructions in the used expression just before the operation using
+        // its value.
+        rewriter.setInsertionPoint(&op);
+        IRMapping mapper;
+        for (Operation &opToClone :
+             usedExpression.getBody()->without_terminator()) {
+          Operation *clone = rewriter.clone(opToClone, mapper);
+          mapper.map(&opToClone, clone);
+        }
+
+        auto usedYield =
+            cast<YieldOp>(usedExpression.getBody()->getTerminator());
+        Operation *expressionRoot = usedYield.getResult().getDefiningOp();
+        assert(expressionRoot && "Used expression has no root operation");
----------------
simon-camp wrote:

```suggestion
        Operation *expressionRoot = usedExpression.getRootOp();
```

https://github.com/llvm/llvm-project/pull/71631