[CIR][Lowering] Supports varargs in the CallingConvention pass (#1005)

This PR adds several copy-pasted lines and a small test and now var args
seems to work in the calling convention pass

Author: gitoleg

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

@@ -47,8 +47,13 @@ arrangeFreeFunctionLikeCall(LowerTypes &LT, LowerModule &LM,
 
   cir_cconv_assert(!::cir::MissingFeatures::chainCall() && !chainCall && "NYI");
   FnInfoOpts opts = chainCall ? FnInfoOpts::IsChainCall : FnInfoOpts::None;
-  return LT.arrangeLLVMFunctionInfo(fnType.getReturnType(), opts,
-                                    fnType.getInputs(), required);
+
+  SmallVector<Type> argTypes;
+  for (const auto &a : args)
+    argTypes.push_back(a.getType());
+
+  return LT.arrangeLLVMFunctionInfo(fnType.getReturnType(), opts, argTypes,
+                                    required);
 }
 
 /// Adds the formal parameters in FPT to the given prefix. If any parameter in

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

@@ -49,12 +49,15 @@ class RequiredArgs {
     if (!prototype.isVarArg())
       return All;
 
-    cir_cconv_assert_or_abort(!::cir::MissingFeatures::variadicFunctions(),
-                              "NYI");
-    return All; // FIXME(cir): Temporary workaround for the assertion above.
+    return RequiredArgs(prototype.getNumInputs() + additional);
   }
 
   bool allowsOptionalArgs() const { return NumRequired != ~0U; }
+
+  unsigned getNumRequiredArgs() const {
+    assert(allowsOptionalArgs());
+    return NumRequired;
+  }
 };
 
 // Implementation detail of LowerFunctionInfo, factored out so it can be
@@ -149,14 +152,9 @@ class LowerFunctionInfo final
 
   unsigned arg_size() const { return NumArgs; }
 
-  bool isVariadic() const {
-    cir_cconv_assert(!::cir::MissingFeatures::variadicFunctions());
-    return false;
-  }
+  bool isVariadic() const { return Required.allowsOptionalArgs(); }
   unsigned getNumRequiredArgs() const {
-    if (isVariadic())
-      cir_cconv_unreachable("NYI");
-    return arg_size();
+    return isVariadic() ? Required.getNumRequiredArgs() : arg_size();
   }
 
   Type getReturnType() const { return getArgsBuffer()[0].type; }

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

@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -fclangir-call-conv-lowering -emit-cir-flat -mmlir --mlir-print-ir-after=cir-call-conv-lowering %s -o %t.cir
+
+int printf(const char *str, ...);
+
+// CHECK: cir.func {{.*@bar}}
+// CHECK:   %[[#V1:]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["a", init]
+// CHECK:   %[[#V2:]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["b", init]
+// CHECK:   cir.store %arg0, %[[#V0]] : !s32i, !cir.ptr<!s32i>
+// CHECK:   cir.store %arg1, %[[#V1]] : !s32i, !cir.ptr<!s32i>
+// CHECK:   %[[#V2:]] = cir.get_global @".str" : !cir.ptr<!cir.array<!s8i x 7>>
+// CHECK:   %[[#V3:]] = cir.cast(array_to_ptrdecay, %[[#V2]] : !cir.ptr<!cir.array<!s8i x 7>>), !cir.ptr<!s8i>
+// CHECK:   %[[#V4:]] = cir.load %[[#V1]] : !cir.ptr<!s32i>, !s32i
+// CHECK:   %[[#V5:]] = cir.load %[[#V2]] : !cir.ptr<!s32i>, !s32i
+// CHECK:   %[[#V6:]] = cir.call @printf(%[[#V3]], %[[#V4]], %[[#V5]]) : (!cir.ptr<!s8i>, !s32i, !s32i) -> !s32i
+void bar(int a, int b) {
+  printf("%d %d\n", a, b);
+}