[clang] [CIR] Emit allocas into the proper lexical scope (PR #132468)

[Andy Kaylor via cfe-commits]

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@@ -0,0 +1,81 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "PassDetail.h"
+#include "mlir/Dialect/Func/IR/FuncOps.h"
+#include "mlir/IR/PatternMatch.h"
+#include "mlir/Support/LogicalResult.h"
+#include "mlir/Transforms/DialectConversion.h"
+#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
+#include "clang/CIR/Dialect/IR/CIRDialect.h"
+#include "clang/CIR/Dialect/Passes.h"
+#include "clang/CIR/MissingFeatures.h"
+#include "llvm/Support/TimeProfiler.h"
+
+using namespace mlir;
+using namespace cir;
+
+namespace {
+
+struct HoistAllocasPass : public HoistAllocasBase<HoistAllocasPass> {
+
+  HoistAllocasPass() = default;
+  void runOnOperation() override;
+};
+
+static void process(mlir::ModuleOp mod, cir::FuncOp func) {
+  if (func.getRegion().empty())
+    return;
+
+  // Hoist all static allocas to the entry block.
+  mlir::Block &entryBlock = func.getRegion().front();
+  llvm::SmallVector<cir::AllocaOp> allocas;
+  func.getBody().walk([&](cir::AllocaOp alloca) {
+    if (alloca->getBlock() == &entryBlock)
+      return;
+    // Don't hoist allocas with dynamic alloca size.
+    assert(!cir::MissingFeatures::opAllocaDynAllocSize());
+    allocas.push_back(alloca);
+  });
+  if (allocas.empty())
+    return;
+
+  mlir::Operation *insertPoint = &*entryBlock.begin();
+
+  for (cir::AllocaOp alloca : allocas) {
+    // Preserving the `const` attribute on hoisted allocas can cause LLVM to
+    // incorrectly introduce invariant group metadata in some circumstances.
+    // The incubator performs some analysis to determine whether the attribute
+    // can be preserved, but it only runs this analysis when optimizations are
+    // enabled. Until we start tracking the optimization level, we can just
+    // always remove the `const` attribute.
+    assert(!cir::MissingFeatures::optInfoAttr());
+    if (alloca.getConstant())
+      alloca.setConstant(false);
+
+    alloca->moveBefore(insertPoint);
+  }
+}
+
+void HoistAllocasPass::runOnOperation() {
+  llvm::TimeTraceScope scope("Hoist Allocas");
+  llvm::SmallVector<Operation *, 16> ops;
+
+  Operation *op = getOperation();
+  auto mod = mlir::dyn_cast<mlir::ModuleOp>(op);
+  if (!mod)
+    mod = op->getParentOfType<mlir::ModuleOp>();
+
+  getOperation()->walk([&](cir::FuncOp op) { process(mod, op); });
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andykaylor wrote:

It looks like the incubator is generating lambdas as separate functions. I'll give the suggested change a try.

https://github.com/llvm/llvm-project/pull/132468