[CIR][LowerToLLVM][CXXABI] Lower cir.va.arg (llvm#573)

lowering var_arg op for ARM64 architecture. This is CIR lowering.

This PR modified LoweringPrepare CXXABI code to make
LoweringPrepareArm64CXXABI class inherit more generic
LoweringPrepareItaniumCXXABI, this way lowering var_arg would be only
meaningful for arm64 targets and for other arch its no op for now.

The ABI doc and detailed algorithm description can be found in this
official doc.

[](https://github.com/ARM-software/abi-aa/blob/617079d8a0d45bec83d351974849483cf0cc66d5/aapcs64/aapcs64.rst#appendix-variable-argument-lists)

clang/include/clang/CIR/Dialect/Builder/CIRBaseBuilder.h

@@ -269,6 +269,19 @@ class CIRBaseBuilderTy : public mlir::OpBuilder {
     return createCast(mlir::cir::CastKind::int_to_ptr, src, newTy);
   }
 
+  mlir::Value createGetMemberOp(mlir::Location &loc, mlir::Value structPtr,
+                                const char *fldName, unsigned idx) {
+
+    assert(structPtr.getType().isa<mlir::cir::PointerType>());
+    auto structBaseTy =
+        structPtr.getType().cast<mlir::cir::PointerType>().getPointee();
+    assert(structBaseTy.isa<mlir::cir::StructType>());
+    auto fldTy = structBaseTy.cast<mlir::cir::StructType>().getMembers()[idx];
+    auto fldPtrTy = ::mlir::cir::PointerType::get(getContext(), fldTy);
+    return create<mlir::cir::GetMemberOp>(loc, fldPtrTy, structPtr, fldName,
+                                          idx);
+  }
+
   mlir::Value createPtrToInt(mlir::Value src, mlir::Type newTy) {
     return createCast(mlir::cir::CastKind::ptr_to_int, src, newTy);
   }

clang/lib/CIR/Dialect/IR/MissingFeatures.h

@@ -21,6 +21,15 @@ struct MissingFeatures {
   // C++ ABI support
   static bool cxxABI() { return false; }
   static bool setCallingConv() { return false; }
+  static bool handleBigEndian() { return false; }
+  static bool handleAArch64Indirect() { return false; }
+  static bool classifyArgumentTypeForAArch64() { return false; }
+  static bool supportgetCoerceToTypeForAArch64() { return false; }
+  static bool supportTySizeQueryForAArch64() { return false; }
+  static bool supportTyAlignQueryForAArch64() { return false; }
+  static bool supportisHomogeneousAggregateQueryForAArch64() { return false; }
+  static bool supportisEndianQueryForAArch64() { return false; }
+  static bool supportisAggregateTypeForABIAArch64() { return false; }
 
   // Address space related
   static bool addressSpace() { return false; }

clang/lib/CIR/Dialect/Transforms/CMakeLists.txt

@@ -2,6 +2,7 @@ add_clang_library(MLIRCIRTransforms
   LifetimeCheck.cpp
   LoweringPrepare.cpp
   LoweringPrepareItaniumCXXABI.cpp
+  LoweringPrepareAArch64CXXABI.cpp
   MergeCleanups.cpp
   DropAST.cpp
   IdiomRecognizer.cpp

clang/lib/CIR/Dialect/Transforms/LoweringPrepare.cpp

@@ -15,7 +15,9 @@
 #include "clang/AST/CharUnits.h"
 #include "clang/AST/Mangle.h"
 #include "clang/Basic/Module.h"
+#include "clang/Basic/TargetInfo.h"
 #include "clang/CIR/Dialect/Builder/CIRBaseBuilder.h"
+#include "clang/CIR/Dialect/IR/CIRDataLayout.h"
 #include "clang/CIR/Dialect/IR/CIRDialect.h"
 #include "clang/CIR/Dialect/Passes.h"
 #include "clang/CIR/Interfaces/ASTAttrInterfaces.h"
@@ -70,6 +72,7 @@ struct LoweringPreparePass : public LoweringPrepareBase<LoweringPreparePass> {
 
   void runOnOp(Operation *op);
   void lowerThreeWayCmpOp(CmpThreeWayOp op);
+  void lowerVAArgOp(VAArgOp op);
   void lowerGlobalOp(GlobalOp op);
   void lowerDynamicCastOp(DynamicCastOp op);
   void lowerStdFindOp(StdFindOp op);
@@ -108,15 +111,24 @@ struct LoweringPreparePass : public LoweringPrepareBase<LoweringPreparePass> {
 
   void setASTContext(clang::ASTContext *c) {
     astCtx = c;
+    auto abiStr = c->getTargetInfo().getABI();
     switch (c->getCXXABIKind()) {
     case clang::TargetCXXABI::GenericItanium:
+      cxxABI.reset(::cir::LoweringPrepareCXXABI::createItaniumABI());
+      break;
     case clang::TargetCXXABI::GenericAArch64:
     case clang::TargetCXXABI::AppleARM64:
-      // TODO: this isn't quite right, clang uses AppleARM64CXXABI which
-      // inherits from ARMCXXABI. We'll have to follow suit.
-      cxxABI.reset(::cir::LoweringPrepareCXXABI::createItaniumABI());
+      // TODO: This is temporary solution. ABIKind info should be
+      // propagated from the targetInfo managed by ABI lowering
+      // query system.
+      assert(abiStr == "aapcs" || abiStr == "darwinpcs" ||
+             abiStr == "aapcs-soft");
+      cxxABI.reset(::cir::LoweringPrepareCXXABI::createAArch64ABI(
+          abiStr == "aapcs"
+              ? ::cir::AArch64ABIKind::AAPCS
+              : (abiStr == "darwinpccs" ? ::cir::AArch64ABIKind::DarwinPCS
+                                        : ::cir::AArch64ABIKind::AAPCSSoft)));
       break;
-
     default:
       llvm_unreachable("NYI");
     }
@@ -320,6 +332,19 @@ static void canonicalizeIntrinsicThreeWayCmp(CIRBaseBuilderTy &builder,
   op.erase();
 }
 
+void LoweringPreparePass::lowerVAArgOp(VAArgOp op) {
+  CIRBaseBuilderTy builder(getContext());
+  builder.setInsertionPoint(op);
+  ::cir::CIRDataLayout datalayout(theModule);
+
+  auto res = cxxABI->lowerVAArg(builder, op, datalayout);
+  if (res) {
+    op.replaceAllUsesWith(res);
+    op.erase();
+  }
+  return;
+}
+
 void LoweringPreparePass::lowerThreeWayCmpOp(CmpThreeWayOp op) {
   CIRBaseBuilderTy builder(getContext());
   builder.setInsertionPointAfter(op);
@@ -603,6 +628,8 @@ void LoweringPreparePass::lowerIterEndOp(IterEndOp op) {
 void LoweringPreparePass::runOnOp(Operation *op) {
   if (auto threeWayCmp = dyn_cast<CmpThreeWayOp>(op)) {
     lowerThreeWayCmpOp(threeWayCmp);
+  } else if (auto vaArgOp = dyn_cast<VAArgOp>(op)) {
+    lowerVAArgOp(vaArgOp);
   } else if (auto getGlobal = dyn_cast<GlobalOp>(op)) {
     lowerGlobalOp(getGlobal);
   } else if (auto dynamicCast = dyn_cast<DynamicCastOp>(op)) {
@@ -635,8 +662,9 @@ void LoweringPreparePass::runOnOperation() {
 
   SmallVector<Operation *> opsToTransform;
   op->walk([&](Operation *op) {
-    if (isa<CmpThreeWayOp, GlobalOp, DynamicCastOp, StdFindOp, IterEndOp,
-            IterBeginOp, ArrayCtor, ArrayDtor, mlir::cir::FuncOp>(op))
+    if (isa<CmpThreeWayOp, VAArgOp, GlobalOp, DynamicCastOp, StdFindOp,
+            IterEndOp, IterBeginOp, ArrayCtor, ArrayDtor, mlir::cir::FuncOp>(
+            op))
       opsToTransform.push_back(op);
   });