[mono][hotreload] Generate seq_points if we don't have pdb information from HotReload (#93039)

* Generating seq_points if we don't have pdb information from HotReload

* Apply suggestions from code review

Co-authored-by: Aleksey Kliger (λgeek) <akliger@gmail.com>

* Addressing @lambdageek comments

---------

Co-authored-by: Aleksey Kliger (λgeek) <akliger@gmail.com>

Author: thaystg

src/mono/mono/metadata/debug-internals.h

@@ -112,4 +112,6 @@ mono_debug_lookup_source_location_by_il (MonoMethod *method, guint32 il_offset,
 MONO_COMPONENT_API char*
 mono_debug_image_get_sourcelink (MonoImage *image);
 
+mono_bool
+mono_debug_generate_enc_seq_points_without_debug_info (MonoDebugMethodInfo *minfo);
 #endif /* __DEBUG_INTERNALS_H__ */

src/mono/mono/metadata/mono-debug.c

@@ -1127,6 +1127,21 @@ mono_debug_enabled (void)
 	return mono_debug_format != MONO_DEBUG_FORMAT_NONE;
 }
 
+
+//Returns true if the method has updates but doesn't have ppdb information then we should generate the seq points using the coreclr rules
+mono_bool
+mono_debug_generate_enc_seq_points_without_debug_info (MonoDebugMethodInfo *minfo)
+{
+	MonoImage* img = m_class_get_image (minfo->method->klass);
+	if (G_UNLIKELY (img->has_updates)) {
+		guint32 idx = mono_metadata_token_index (minfo->method->token);
+		MonoDebugInformationEnc *mdie = (MonoDebugInformationEnc *) mono_metadata_update_get_updated_method_ppdb (img, idx);
+		if (mdie == NULL)
+			return TRUE;
+	}
+	return FALSE;
+}
+
 void
 mono_debug_get_seq_points (MonoDebugMethodInfo *minfo, char **source_file, GPtrArray **source_file_list, int **source_files, MonoSymSeqPoint **seq_points, int *n_seq_points)
 {

src/mono/mono/mini/interp/transform.c

@@ -4782,6 +4782,19 @@ is_ip_protected (MonoMethodHeader *header, int offset)
 	return FALSE;
 }
 
+static gboolean
+should_insert_seq_point (TransformData *td)
+{
+	//following the CoreCLR's algorithm for adding the sequence points
+	if ((*td->ip == CEE_NOP) ||
+		(*td->ip == CEE_CALLVIRT) ||
+		(*td->ip == CEE_CALLI) ||
+		(*td->ip == CEE_CALL) ||
+		(GPTRDIFF_TO_INT (td->sp - td->stack) == 0))
+		return TRUE;
+	return FALSE;
+}
+
 static gboolean
 generate_code (TransformData *td, MonoMethod *method, MonoMethodHeader *header, MonoGenericContext *generic_context, MonoError *error)
 {
@@ -4813,6 +4826,7 @@ generate_code (TransformData *td, MonoMethod *method, MonoMethodHeader *header,
 	gboolean save_last_error = FALSE;
 	gboolean link_bblocks = TRUE;
 	gboolean inlining = td->method != method;
+	gboolean generate_enc_seq_points_without_debug_info = FALSE;
 	InterpBasicBlock *exit_bb = NULL;
 
 	original_bb = bb = mono_basic_block_split (method, error, header);
@@ -4859,6 +4873,8 @@ generate_code (TransformData *td, MonoMethod *method, MonoMethodHeader *header,
 			int n_il_offsets;
 
 			mono_debug_get_seq_points (minfo, NULL, NULL, NULL, &sps, &n_il_offsets);
+			if (n_il_offsets == 0)
+				generate_enc_seq_points_without_debug_info = mono_debug_generate_enc_seq_points_without_debug_info (minfo);
 			// FIXME: Free
 			seq_point_locs = mono_bitset_mem_new (mono_mempool_alloc0 (td->mempool, mono_bitset_alloc_size (header->code_size, 0)), header->code_size, 0);
 			sym_seq_points = TRUE;
@@ -5084,6 +5100,9 @@ generate_code (TransformData *td, MonoMethod *method, MonoMethodHeader *header,
 			WRITE64_INS (td->last_ins, 0, &counter);
 		}
 
+		if (G_UNLIKELY (generate_enc_seq_points_without_debug_info) && should_insert_seq_point (td))
+			last_seq_point = interp_add_ins (td, MINT_SDB_SEQ_POINT);
+
 		switch (*td->ip) {
 		case CEE_NOP:
 			/* lose it */
@@ -5353,7 +5372,7 @@ generate_code (TransformData *td, MonoMethod *method, MonoMethodHeader *header,
 			if (!interp_transform_call (td, method, NULL, generic_context, constrained_class, readonly, error, TRUE, save_last_error, tailcall))
 				goto exit;
 
-			if (need_seq_point) {
+			if (need_seq_point && !generate_enc_seq_points_without_debug_info) {
 				// check if it is a nested call and remove the MONO_INST_NONEMPTY_STACK of the last breakpoint, only for non native methods
 				if (!(method->flags & METHOD_IMPL_ATTRIBUTE_NATIVE)) {
 					if (emitted_funccall_seq_point)	{