Will data precision affect uniform block layout?


I am using std140 for Uniform Block Layout, I defined a simple uniform block like below:

on the cpu side, I defined the structure like
MyTestStruct {
Vector4 FinalColor1;

Vector4 FinalColor2;

Vector4 ColorIndex;

Vector4 FinalColor3;


I tested mediump data precision in the shader and It works on my android phone with MaliG76. but I don't known if this is valid on all mali gpu.

layout(binding = 0, std140) uniform MyTestBlock {
mediump vec4 FinalColor1;
mediump vec4 FinalColor2;
mediump vec4 ColorIndex;
mediump vec4 FinalColor3;

Will there be a default highp->mediump conversion? If Yes, is it on every shader execution or is there a special optimization?