Fix #19633 by proper store to &ubo_data.shadow_matrix[1234].

It is not valid in C++ to store into shadow_matrix1[16] with shadow_matrix1[16 * j]
(for j > 0). Even though there's a valid space in a struct after shadow_matrix1.
Knowing that GCC performs aggressive optimizations that eventually lead
to a wrong code. Code has been changed into union where one can either
use shadow_matrix[4 * 16], or individual shadow_matrix1, shadow_matrix2, etc. GCC pragma
is not needed any longer.

2 files changed, 12 insertions, 17 deletions

diff --git a/drivers/gles3/rasterizer_scene_gles3.cpp b/drivers/gles3/rasterizer_scene_gles3.cpp
index d53b27eb88..1fba8535d8 100644
--- a/drivers/gles3/rasterizer_scene_gles3.cpp
+++ b/drivers/gles3/rasterizer_scene_gles3.cpp
@@ -2677,13 +2677,6 @@ void RasterizerSceneGLES3::_setup_environment(Environment *env, const CameraMatr
 	glBindBuffer(GL_UNIFORM_BUFFER, 0);
 }
 
-// Drop -O3 for this function as it triggers a GCC bug up until at least GCC 8.2.1.
-// This refers to GH issue #19633.
-// The bug has been reported to the GCC project.
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC push_options
-#pragma GCC optimize("-O2")
-#endif
 void RasterizerSceneGLES3::_setup_directional_light(int p_index, const Transform &p_camera_inverse_transform, bool p_use_shadows) {
 
 	LightInstance *li = directional_lights[p_index];
@@ -2784,7 +2777,7 @@ void RasterizerSceneGLES3::_setup_directional_light(int p_index, const Transform
 
 			CameraMatrix shadow_mtx = rectm * bias * li->shadow_transform[j].camera * modelview;
 
-			store_camera(shadow_mtx, &ubo_data.shadow_matrix1[16 * j]);
+			store_camera(shadow_mtx, &ubo_data.shadow.matrix[16 * j]);
 
 			ubo_data.light_clamp[0] = atlas_rect.position.x;
 			ubo_data.light_clamp[1] = atlas_rect.position.y;
@@ -2801,9 +2794,6 @@ void RasterizerSceneGLES3::_setup_directional_light(int p_index, const Transform
 
 	glBindBufferBase(GL_UNIFORM_BUFFER, 3, state.directional_ubo);
 }
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC pop_options
-#endif
 
 void RasterizerSceneGLES3::_setup_lights(RID *p_light_cull_result, int p_light_cull_count, const Transform &p_camera_inverse_transform, const CameraMatrix &p_camera_projection, RID p_shadow_atlas) {
 
@@ -2898,7 +2888,7 @@ void RasterizerSceneGLES3::_setup_lights(RID *p_light_cull_result, int p_light_c
 
 					Transform proj = (p_camera_inverse_transform * li->transform).inverse();
 
-					store_transform(proj, ubo_data.shadow_matrix1);
+					store_transform(proj, ubo_data.shadow.matrix1);
 
 					ubo_data.light_params[3] = 1.0; //means it has shadow
 					ubo_data.light_clamp[0] = float(x) / atlas_size;
@@ -2987,7 +2977,7 @@ void RasterizerSceneGLES3::_setup_lights(RID *p_light_cull_result, int p_light_c
 
 					CameraMatrix shadow_mtx = rectm * bias * li->shadow_transform[0].camera * modelview;
 
-					store_camera(shadow_mtx, ubo_data.shadow_matrix1);
+					store_camera(shadow_mtx, ubo_data.shadow.matrix1);
 				}
 
 				li->light_index = state.spot_light_count;
diff --git a/drivers/gles3/rasterizer_scene_gles3.h b/drivers/gles3/rasterizer_scene_gles3.h
index 9772b5dd23..325617745a 100644
--- a/drivers/gles3/rasterizer_scene_gles3.h
+++ b/drivers/gles3/rasterizer_scene_gles3.h
@@ -569,10 +569,15 @@ public:
 		float light_params[4]; //spot attenuation, spot angle, specular, shadow enabled
 		float light_clamp[4];
 		float light_shadow_color_contact[4];
-		float shadow_matrix1[16]; //up to here for spot and omni, rest is for directional
-		float shadow_matrix2[16];
-		float shadow_matrix3[16];
-		float shadow_matrix4[16];
+		union {
+			struct {
+				float matrix1[16]; //up to here for spot and omni, rest is for directional
+				float matrix2[16];
+				float matrix3[16];
+				float matrix4[16];
+			};
+			float matrix[4 * 16];
+		} shadow;
 		float shadow_split_offsets[4];
 	};