glsl-out: Call proper memory barrier functions (#1680)

* glsl-out: Call proper memory barrier functions

* glsl-out: Change test for control flow

* Removed two unnecessary calls

src/back/glsl/mod.rs

@@ -1771,13 +1771,18 @@ impl<'a, W: Write> Writer<'a, W> {
             // keyword which ceases all further processing in a fragment shader, it's called OpKill
             // in spir-v that's why it's called `Statement::Kill`
             Statement::Kill => writeln!(self.out, "{}discard;", level)?,
-            // Issue an execution or a memory barrier.
+            // Issue a memory barrier. Please note that to ensure visibility,
+            // OpenGL always requires a call to the `barrier()` function after a `memoryBarrier*()`
             Statement::Barrier(flags) => {
-                if flags.is_empty() {
-                    writeln!(self.out, "{}barrier();", level)?;
-                } else {
-                    writeln!(self.out, "{}groupMemoryBarrier();", level)?;
+                if flags.contains(crate::Barrier::STORAGE) {
+                    writeln!(self.out, "{}memoryBarrierBuffer();", level)?;
+                }
+
+                if flags.contains(crate::Barrier::WORK_GROUP) {
+                    writeln!(self.out, "{}memoryBarrierShared();", level)?;
                 }
+
+                writeln!(self.out, "{}barrier();", level)?;
             }
             // Stores in glsl are just variable assignments written as `pointer = value;`
             Statement::Store { pointer, value } => {

tests/out/glsl/control-flow.main.Compute.glsl

@@ -38,8 +38,10 @@ void loop_switch_continue(int x) {
 void main() {
     uvec3 global_id = gl_GlobalInvocationID;
     int pos = 0;
-    groupMemoryBarrier();
-    groupMemoryBarrier();
+    memoryBarrierBuffer();
+    barrier();
+    memoryBarrierShared();
+    barrier();
     switch(1) {
         default:
             pos = 1;