GLSL: Implement switch on ESSL 1.0.

Cannot use switch on legacy ESSL, fallback to plain branches.

reference/opt/shaders/legacy/fragment/switch.legacy.frag

@@ -0,0 +1,77 @@
+#version 100
+precision mediump float;
+precision highp int;
+
+varying highp float vIndexF;
+
+void main()
+{
+    int _13 = int(vIndexF);
+    highp vec4 _65;
+    highp vec4 _66;
+    highp vec4 _68;
+    for (int SPIRV_Cross_Dummy = 0; SPIRV_Cross_Dummy < 1; SPIRV_Cross_Dummy++)
+    {
+        if (_13 == 2)
+        {
+            _68 = vec4(0.0, 2.0, 3.0, 4.0);
+            break;
+        }
+        else if ((_13 == 4) || (_13 == 5))
+        {
+            _68 = vec4(1.0, 2.0, 3.0, 4.0);
+            break;
+        }
+        else if ((_13 == 8) || (_13 == 9))
+        {
+            _68 = vec4(40.0, 20.0, 30.0, 40.0);
+            break;
+        }
+        else if (_13 == 10)
+        {
+            _65 = vec4(10.0);
+            highp vec4 _45 = _65 + vec4(1.0);
+            _66 = _45;
+            highp vec4 _48 = _66 + vec4(2.0);
+            _68 = _48;
+            break;
+        }
+        else if (_13 == 11)
+        {
+            _65 = vec4(0.0);
+            highp vec4 _45 = _65 + vec4(1.0);
+            _66 = _45;
+            highp vec4 _48 = _66 + vec4(2.0);
+            _68 = _48;
+            break;
+        }
+        else if (_13 == 12)
+        {
+            _66 = vec4(0.0);
+            highp vec4 _48 = _66 + vec4(2.0);
+            _68 = _48;
+            break;
+        }
+        else
+        {
+            _68 = vec4(10.0, 20.0, 30.0, 40.0);
+            break;
+        }
+    }
+    highp vec4 _70;
+    for (int SPIRV_Cross_Dummy = 0; SPIRV_Cross_Dummy < 1; SPIRV_Cross_Dummy++)
+    {
+        if ((_13 == 10) || (_13 == 20))
+        {
+            _70 = vec4(40.0);
+            break;
+        }
+        else
+        {
+            _70 = vec4(20.0);
+            break;
+        }
+    }
+    gl_FragData[0] = _68 + _70;
+}
+

reference/shaders-hlsl-no-opt/asm/frag/switch-block-case-fallthrough.asm.invalid.frag

@@ -17,14 +17,6 @@ void frag_main()
     int j;
     int _30;
     int _31;
-    if (vIndex != 0 && vIndex != 1 && vIndex != 11 && vIndex != 2 && vIndex != 3 && vIndex != 4 && vIndex != 5)
-    {
-        _30 = 2;
-    }
-    if (vIndex == 1 || vIndex == 11)
-    {
-        _31 = 1;
-    }
     switch (vIndex)
     {
         case 0:
@@ -37,6 +29,7 @@ void frag_main()
         }
         default:
         {
+            _30 = 2;
             j = _30;
             _31 = 0;
             j = _31;
@@ -45,6 +38,7 @@ void frag_main()
         case 1:
         case 11:
         {
+            _31 = 1;
             j = _31;
             break;
         }

reference/shaders/legacy/fragment/switch.legacy.frag

@@ -0,0 +1,78 @@
+#version 100
+precision mediump float;
+precision highp int;
+
+varying highp float vIndexF;
+
+void main()
+{
+    int vIndex = int(vIndexF);
+    highp vec4 v = vec4(0.0);
+    for (int SPIRV_Cross_Dummy = 0; SPIRV_Cross_Dummy < 1; SPIRV_Cross_Dummy++)
+    {
+        if (vIndex == 2)
+        {
+            v = vec4(0.0, 2.0, 3.0, 4.0);
+            break;
+        }
+        else if ((vIndex == 4) || (vIndex == 5))
+        {
+            v = vec4(1.0, 2.0, 3.0, 4.0);
+            break;
+        }
+        else if ((vIndex == 8) || (vIndex == 9))
+        {
+            v = vec4(40.0, 20.0, 30.0, 40.0);
+            break;
+        }
+        else if (vIndex == 10)
+        {
+            v = vec4(10.0);
+            highp vec4 _43 = v;
+            highp vec4 _44 = vec4(1.0);
+            highp vec4 _45 = _43 + _44;
+            v = _45;
+            highp vec4 _46 = v;
+            highp vec4 _47 = vec4(2.0);
+            highp vec4 _48 = _46 + _47;
+            v = _48;
+            break;
+        }
+        else if (vIndex == 11)
+        {
+            highp vec4 _43 = v;
+            highp vec4 _44 = vec4(1.0);
+            highp vec4 _45 = _43 + _44;
+            v = _45;
+            highp vec4 _46 = v;
+            highp vec4 _47 = vec4(2.0);
+            highp vec4 _48 = _46 + _47;
+            v = _48;
+            break;
+        }
+        else if (vIndex == 12)
+        {
+            highp vec4 _46 = v;
+            highp vec4 _47 = vec4(2.0);
+            highp vec4 _48 = _46 + _47;
+            v = _48;
+            break;
+        }
+        else
+        {
+            v = vec4(10.0, 20.0, 30.0, 40.0);
+            break;
+        }
+    }
+    highp vec4 w = vec4(20.0);
+    for (int SPIRV_Cross_Dummy = 0; SPIRV_Cross_Dummy < 1; SPIRV_Cross_Dummy++)
+    {
+        if ((vIndex == 10) || (vIndex == 20))
+        {
+            w = vec4(40.0);
+            break;
+        }
+    }
+    gl_FragData[0] = v + w;
+}
+

shaders/legacy/fragment/switch.legacy.frag

@@ -0,0 +1,43 @@
+#version 450
+
+layout(location = 0) out vec4 FragColor;
+layout(location = 0) in float vIndexF;
+
+void main()
+{
+	int vIndex = int(vIndexF);
+	vec4 v = vec4(0.0);
+	switch (vIndex)
+	{
+	case 2:
+		v = vec4(0, 2, 3, 4);
+		break;
+	case 4:
+	case 5:
+		v = vec4(1, 2, 3, 4);
+		break;
+	case 8:
+	case 9:
+		v = vec4(40, 20, 30, 40);
+		break;
+	case 10:
+		v = vec4(10.0);
+	case 11:
+		v += 1.0;
+	case 12:
+		v += 2.0;
+		break;
+	default:
+		v = vec4(10, 20, 30, 40);
+		break;
+	}
+
+	vec4 w = vec4(20.0);
+	switch (vIndex)
+	{
+	case 10:
+	case 20:
+		w = vec4(40.0);
+	}
+	FragColor = v + w;
+}

spirv_glsl.cpp

@@ -539,6 +539,9 @@ string CompilerGLSL::compile()
 	backend.supports_extensions = true;
 	backend.use_array_constructor = true;
 
+	if (is_legacy_es())
+		backend.support_case_fallthrough = false;
+
 	// Scan the SPIR-V to find trivial uses of extensions.
 	fixup_type_alias();
 	reorder_type_alias();
@@ -13272,6 +13275,8 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 			// Order does not matter.
 			if (!injected_block)
 				block_declaration_order.push_back(block.default_block);
+			else if (is_legacy_es())
+				SPIRV_CROSS_THROW("Default case label fallthrough to other case label is not supported in ESSL 1.0.");
 
 			case_constructs[block.default_block] = {};
 		}
@@ -13282,12 +13287,25 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 			return is_unsigned_case ? convert_to_string(literal) : convert_to_string(int32_t(literal));
 		};
 
+		const auto to_legacy_case_label = [&](uint32_t condition, const SmallVector<uint32_t> &labels, const char *suffix) -> string {
+			string ret;
+			size_t count = labels.size();
+			for (size_t i = 0; i < count; i++)
+			{
+				if (i)
+					ret += " || ";
+				ret += join(count > 1 ? "(" : "", to_enclosed_expression(condition), " == ", labels[i], suffix,
+				            count > 1 ? ")" : "");
+			}
+			return ret;
+		};
+
 		// We need to deal with a complex scenario for OpPhi. If we have case-fallthrough and Phi in the picture,
 		// we need to flush phi nodes outside the switch block in a branch,
 		// and skip any Phi handling inside the case label to make fall-through work as expected.
 		// This kind of code-gen is super awkward and it's a last resort. Normally we would want to handle this
 		// inside the case label if at all possible.
-		for (size_t i = 1; i < num_blocks; i++)
+		for (size_t i = 1; backend.support_case_fallthrough && i < num_blocks; i++)
 		{
 			if (flush_phi_required(block.self, block_declaration_order[i]) &&
 			    flush_phi_required(block_declaration_order[i - 1], block_declaration_order[i]))
@@ -13341,7 +13359,7 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 		// This is buggy on FXC, so just emit the logical equivalent of a do { } while(false), which is more idiomatic.
 		bool degenerate_switch = block.default_block != block.merge_block && block.cases.empty();
 
-		if (degenerate_switch)
+		if (degenerate_switch || is_legacy_es())
 		{
 			// ESSL 1.0 is not guaranteed to support do/while.
 			if (is_legacy_es())
@@ -13365,8 +13383,21 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 			{
 				// Default case.
 				if (!degenerate_switch)
+				{
+					if (is_legacy_es())
+						statement("else");
+					else
 						statement("default:");
 				}
+			}
+			else
+			{
+				if (is_legacy_es())
+				{
+					statement((i ? "else " : ""), "if (",
+					          to_legacy_case_label(block.condition, literals, label_suffix),
+					          ")");
+				}
 				else
 				{
 					for (auto &case_literal : literals)
@@ -13375,6 +13406,7 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 						statement("case ", to_case_label(case_literal, unsigned_case), label_suffix, ":");
 					}
 				}
+			}
 
 			auto &case_block = get<SPIRBlock>(target_block);
 			if (backend.support_case_fallthrough && i + 1 < num_blocks &&
@@ -13407,7 +13439,12 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 					statement("case ", to_case_label(case_literal, unsigned_case), label_suffix, ":");
 
 				if (block.default_block == block.next_block)
+				{
+					if (is_legacy_es())
+						statement("else");
+					else
 						statement("default:");
+				}
 
 				begin_scope();
 				flush_phi(block.self, block.next_block);