[CIR][ABI][Lowering] Supports call by function pointer in the calling convention lowering pass (#1034)

This PR adds a support for calls by  function pointers.

@sitio-couto   I think would be great if you'll also take a look

Author: gitoleg

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

@@ -103,7 +103,7 @@ struct CallConvLowering {
     rewriter.setInsertionPoint(op);
     auto typ = op.getIndirectCall().getType();
     if (isFuncPointerTy(typ)) {
-      cir_cconv_unreachable("Indirect calls NYI");
+      lowerModule->rewriteFunctionCall(op);
     }
   }
 

clang/lib/CIR/Dialect/Transforms/TargetLowering/LowerFunction.cpp

@@ -630,8 +630,16 @@ LogicalResult LowerFunction::rewriteCallOp(CallOp op,
   // NOTE(cir): There is no direct way to fetch the function type from the
   // CallOp, so we fetch it from the source function. This assumes the
   // function definition has not yet been lowered.
-  cir_cconv_assert(SrcFn && "No source function");
-  auto fnType = SrcFn.getFunctionType();
+
+  FuncType fnType;
+  if (SrcFn) {
+    fnType = SrcFn.getFunctionType();
+  } else if (op.isIndirect()) {
+    if (auto ptrTy = dyn_cast<PointerType>(op.getIndirectCall().getType()))
+      fnType = dyn_cast<FuncType>(ptrTy.getPointee());
+  }
+
+  cir_cconv_assert(fnType && "No callee function type");
 
   // Rewrite the call operation to abide to the ABI calling convention.
   auto Ret = rewriteCallOp(fnType, SrcFn, op, retValSlot);
@@ -687,7 +695,7 @@ Value LowerFunction::rewriteCallOp(FuncType calleeTy, FuncOp origCallee,
   //
   // Chain calls use this same code path to add the invisible chain parameter
   // to the function type.
-  if (origCallee.getNoProto() || Chain) {
+  if ((origCallee && origCallee.getNoProto()) || Chain) {
     cir_cconv_assert_or_abort(::cir::MissingFeatures::ABINoProtoFunctions(),
                               "NYI");
   }
@@ -870,8 +878,21 @@ Value LowerFunction::rewriteCallOp(const LowerFunctionInfo &CallInfo,
   // NOTE(cir): We don't know if the callee was already lowered, so we only
   // fetch the name from the callee, while the return type is fetch from the
   // lowering types manager.
-  CallOp newCallOp = rewriter.create<CallOp>(
-      loc, Caller.getCalleeAttr(), IRFuncTy.getReturnType(), IRCallArgs);
+
+  CallOp newCallOp;
+
+  if (Caller.isIndirect()) {
+    rewriter.setInsertionPoint(Caller);
+    auto val = Caller.getIndirectCall();
+    auto ptrTy = PointerType::get(val.getContext(), IRFuncTy);
+    auto callee =
+        rewriter.create<CastOp>(val.getLoc(), ptrTy, CastKind::bitcast, val);
+    newCallOp = rewriter.create<CallOp>(loc, callee, IRFuncTy, IRCallArgs);
+  } else {
+    newCallOp = rewriter.create<CallOp>(loc, Caller.getCalleeAttr(),
+                                        IRFuncTy.getReturnType(), IRCallArgs);
+  }
+
   auto extraAttrs =
       rewriter.getAttr<ExtraFuncAttributesAttr>(rewriter.getDictionaryAttr({}));
   newCallOp->setAttr("extra_attrs", extraAttrs);

clang/lib/CIR/Dialect/Transforms/TargetLowering/LowerModule.h

@@ -96,7 +96,7 @@ class LowerModule {
   LogicalResult rewriteFunctionDefinition(FuncOp op);
 
   // Rewrite CIR CallOp to match the target ABI.
-  LogicalResult rewriteFunctionCall(CallOp callOp, FuncOp funcOp);
+  LogicalResult rewriteFunctionCall(CallOp callOp, FuncOp funcOp = {});
 };
 
 std::unique_ptr<LowerModule> createLowerModule(ModuleOp module,

clang/test/CIR/CallConvLowering/x86_64/fptrs.c

@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir-flat -fclangir-call-conv-lowering %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm -fclangir-call-conv-lowering %s -o -| FileCheck %s -check-prefix=LLVM
 
 typedef struct {
   int a;
@@ -16,3 +17,31 @@ int foo(S s) { return 42 + s.a; }
 void bar() {
   myfptr a = foo;
 }
+
+// CHECK: cir.func {{.*@baz}}(%arg0: !s32i
+// CHECK:   %[[#V0:]] = cir.alloca !ty_S, !cir.ptr<!ty_S>, [""] {alignment = 4 : i64}
+// CHECK:   %[[#V1:]] = cir.cast(bitcast, %[[#V0]] : !cir.ptr<!ty_S>), !cir.ptr<!s32i>
+// CHECK:   cir.store %arg0, %[[#V1]] : !s32i, !cir.ptr<!s32i>
+// CHECK:   %[[#V2:]] = cir.alloca !cir.ptr<!cir.func<!s32i (!ty_S)>>, !cir.ptr<!cir.ptr<!cir.func<!s32i (!ty_S)>>>, ["a", init]
+// CHECK:   %[[#V3:]] = cir.get_global @foo : !cir.ptr<!cir.func<!s32i (!s32i)>>
+// CHECK:   %[[#V4:]] = cir.cast(bitcast, %[[#V3]] : !cir.ptr<!cir.func<!s32i (!s32i)>>), !cir.ptr<!cir.func<!s32i (!ty_S)>>
+// CHECK:   cir.store %[[#V4]], %[[#V2]] : !cir.ptr<!cir.func<!s32i (!ty_S)>>, !cir.ptr<!cir.ptr<!cir.func<!s32i (!ty_S)>>>
+// CHECK:   %[[#V5:]] = cir.load %[[#V2]] : !cir.ptr<!cir.ptr<!cir.func<!s32i (!ty_S)>>>, !cir.ptr<!cir.func<!s32i (!ty_S)>>
+// CHECK:   %[[#V6:]] = cir.cast(bitcast, %[[#V0]] : !cir.ptr<!ty_S>), !cir.ptr<!s32i>
+// CHECK:   %[[#V7:]] = cir.load %[[#V6]] : !cir.ptr<!s32i>, !s32i
+// CHECK:   %[[#V8:]] = cir.cast(bitcast, %[[#V5]] : !cir.ptr<!cir.func<!s32i (!ty_S)>>), !cir.ptr<!cir.func<!s32i (!s32i)>>
+// CHECK:   %[[#V9:]] = cir.call %[[#V8]](%[[#V7]]) : (!cir.ptr<!cir.func<!s32i (!s32i)>>, !s32i) -> !s32i
+
+// LLVM: define dso_local void @baz(i32 %0)
+// LLVM:   %[[#V1:]] = alloca %struct.S, i64 1
+// LLVM:   store i32 %0, ptr %[[#V1]]
+// LLVM:   %[[#V2:]] = alloca ptr, i64 1
+// LLVM:   store ptr @foo, ptr %[[#V2]]
+// LLVM:   %[[#V3:]] = load ptr, ptr %[[#V2]]
+// LLVM:   %[[#V4:]] = load i32, ptr %[[#V1]]
+// LLVM:   %[[#V5:]] = call i32 %[[#V3]](i32 %[[#V4]])
+
+void baz(S s) {
+  myfptr a = foo;
+  a(s);
+}