[clang] [mlir] [CIR] Add CIRABIRewriteContext for ABI function/call rewriting (PR #192119)

[Andy Kaylor via cfe-commits]

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@@ -0,0 +1,469 @@
+//===- CIRABIRewriteContext.cpp - CIR-specific ABI rewriting --------------===//
+//
+// 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 "CIRABIRewriteContext.h"
+#include "mlir/IR/Builders.h"
+#include "mlir/IR/Types.h"
+#include "clang/CIR/Dialect/IR/CIRAttrs.h"
+#include "clang/CIR/Dialect/IR/CIRDialect.h"
+#include "clang/CIR/Dialect/IR/CIROpsEnums.h"
+
+using namespace cir;
+using namespace mlir;
+using namespace mlir::abi;
+
+/// Emit a value coercion between two types.  For scalar-to-scalar
+/// (e.g. integer sign extension), a direct cir.cast is sufficient.
+/// When one of the types is a record (struct), LLVM IR's bitcast
+/// cannot reinterpret between aggregate and scalar types, so we go
+/// through memory: alloca srcTy -> store src -> bitcast ptr -> load
+/// dstTy.
+static Value emitCoercion(OpBuilder &rewriter, Location loc, Type dstTy,
+                          Value src) {
+  Type srcTy = src.getType();
+  if (srcTy == dstTy)
+    return src;
+
+  bool needsMemory =
+      mlir::isa<cir::RecordType, cir::ComplexType>(srcTy) ||
+      mlir::isa<cir::RecordType, cir::ComplexType>(dstTy) ||
+      (mlir::isa<cir::VectorType>(srcTy) != mlir::isa<cir::VectorType>(dstTy));
+
+  if (!needsMemory)
+    return cir::CastOp::create(rewriter, loc, dstTy, cir::CastKind::bitcast,
+                               src);
+
+  auto srcPtrTy = cir::PointerType::get(srcTy);
+  auto dstPtrTy = cir::PointerType::get(dstTy);
+
+  auto alloca =
+      cir::AllocaOp::create(rewriter, loc, srcPtrTy, srcTy,
+                            /*name=*/rewriter.getStringAttr("coerce"),
+                            /*alignment=*/rewriter.getI64IntegerAttr(8));
----------------
andykaylor wrote:

The alignment here seems quite arbitrary.

https://github.com/llvm/llvm-project/pull/192119