[cxx] Fixes for all lanes to build as C++ but w/o configure.ac change. (

mono/mono#17452)

* [cxx] dlmalloc remove extern "C" and remove NO_MALLINFO.

* [cxx] Move CallInst bitfields to the end to minimize padding for alignment
and fix an unexplained LLVM problem.


Commit migrated from mono/mono@dc866c2

src/mono/mono/mini/mini.h

@@ -783,16 +783,34 @@ struct MonoCallInst {
 	MonoInst *out_args;
 	MonoInst *vret_var;
 	gconstpointer fptr;
+	MonoJitICallId jit_icall_id;
 	guint stack_usage;
 	guint stack_align_amount;
+	regmask_t used_iregs;
+	regmask_t used_fregs;
+	GSList *out_ireg_args;
+	GSList *out_freg_args;
+	GSList *outarg_vts;
+	CallInfo *call_info;
+#ifdef ENABLE_LLVM
+	LLVMCallInfo *cinfo;
+	int rgctx_arg_reg, imt_arg_reg;
+#endif
+#ifdef TARGET_ARM
+	/* See the comment in mini-arm.c!mono_arch_emit_call for RegTypeFP. */
+	GSList *float_args;
+#endif
+	// Bitfields are at the end due to an unexplained problem with C++ and LLVM.
+	// This is also their ideal place to minimize padding for alignment,
+	// unless there is a placement to increase locality.
+
 	guint is_virtual : 1;
 	// FIXME tailcall field is written after read; prefer MONO_IS_TAILCALL_OPCODE.
 	guint tailcall : 1;
 	/* If this is TRUE, 'fptr' points to a MonoJumpInfo instead of an address. */
 	guint fptr_is_patch : 1;
-	MonoJitICallId jit_icall_id;
 	/*
-	 * If this is true, then the call returns a vtype in a register using the same 
+	 * If this is true, then the call returns a vtype in a register using the same
 	 * calling convention as OP_CALL.
 	 */
 	guint vret_in_reg : 1;
@@ -804,20 +822,6 @@ struct MonoCallInst {
 	guint32 rgctx_reg : 1;
 	/* Whenever the call will need an unbox trampoline */
 	guint need_unbox_trampoline : 1;
-	regmask_t used_iregs;
-	regmask_t used_fregs;
-	GSList *out_ireg_args;
-	GSList *out_freg_args;
-	GSList *outarg_vts;
-	CallInfo *call_info;
-#ifdef ENABLE_LLVM
-	LLVMCallInfo *cinfo;
-	int rgctx_arg_reg, imt_arg_reg;
-#endif
-#ifdef TARGET_ARM
-	/* See the comment in mini-arm.c!mono_arch_emit_call for RegTypeFP. */
-	GSList *float_args;
-#endif
 };
 
 struct MonoCallArgParm {

src/mono/mono/utils/dlmalloc.c

@@ -652,10 +652,6 @@ struct mallinfo {
 #endif /* HAVE_USR_INCLUDE_MALLOC_H */
 #endif /* NO_MALLINFO */
 
-#ifdef __cplusplus
-extern "C" {
-#endif /* __cplusplus */
-
 #if !ONLY_MSPACES
 
 /* ------------------- Declarations of public routines ------------------- */
@@ -1146,10 +1142,6 @@ int mspace_mallopt(int, int);
 
 #endif /* MSPACES */
 
-#ifdef __cplusplus
-};  /* end of extern "C" */
-#endif /* __cplusplus */
-
 /*
   ========================================================================
   To make a fully customizable malloc.h header file, cut everything

src/mono/mono/utils/dlmalloc.h

@@ -28,26 +28,6 @@
 #include <stddef.h>   /* for size_t */
 #include <mono/utils/mono-compiler.h>
 
-// Returning an undefined struct by value from extern "C"
-// is sometimes an error. Mono does not use the code (dlmallinfo)..
-//
-// Other fixes:
-//   - define the struct
-//   - #if __cplusplus
-//   - #if HOST_WASM
-//   - #ifndef HAVE_USR_INCLUDE_MALLOC_H
-//   - Make it not extern "C".
-//   - Return the struct through an out parameter.
-//   - remove extern "C" entirely in dlmalloc.
-//
-// Mono does not use the function (dlmallinfo).
-//
-#define NO_MALLINFO 1 /* mono */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #if !ONLY_MSPACES
 
 #ifndef USE_DL_PREFIX
@@ -554,8 +534,4 @@ int mspace_mallopt(int, int);
 
 #endif  /* MSPACES */
 
-#ifdef __cplusplus
-};  /* end of extern "C" */
-#endif
-
 #endif /* MALLOC_280_H */