Sanitize underscores in general, not just for members.

reference/opt/shaders/asm/frag/complex-name-workarounds.asm.frag

@@ -0,0 +1,16 @@
+#version 450
+
+layout(location = 0) in vec4 _;
+layout(location = 1) in vec4 a;
+layout(location = 0) out vec4 b;
+
+void main()
+{
+    vec4 _28 = (_ + a) + _;
+    vec4 _34 = (_ - a) + a;
+    b = _28;
+    b = _34;
+    b = _28;
+    b = _34;
+}
+

reference/shaders/asm/frag/complex-name-workarounds.asm.frag

@@ -0,0 +1,28 @@
+#version 450
+
+layout(location = 0) in vec4 _;
+layout(location = 1) in vec4 a;
+layout(location = 0) out vec4 b;
+
+vec4 fu_nc_(vec4 a_)
+{
+    return a_;
+}
+
+vec4 fu_nc_1(vec4 _0_1)
+{
+    return _0_1;
+}
+
+void main()
+{
+    vec4 b_1 = _;
+    vec4 _0_1 = (_ + a) + fu_nc_(b_1);
+    vec4 b_3 = a;
+    vec4 b_2 = (_ - a) + fu_nc_1(b_3);
+    b = _0_1;
+    b = b_2;
+    b = _0_1;
+    b = b_2;
+}
+

shaders/asm/frag/complex-name-workarounds.asm.frag

@@ -0,0 +1,81 @@
+; SPIR-V
+; Version: 1.0
+; Generator: Khronos Glslang Reference Front End; 6
+; Bound: 47
+; Schema: 0
+               OpCapability Shader
+          %1 = OpExtInstImport "GLSL.std.450"
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %main "main" %a %b %FragColor
+               OpExecutionMode %main OriginUpperLeft
+               OpSource GLSL 450
+               OpName %main "main"
+               OpName %func__vf4_ "fu__nc_"
+               OpName %a_ "a_"
+               OpName %func_2_vf4_ "fu__nc_"
+               OpName %a_2 "___"
+               OpName %c0 "___"
+               OpName %a "__"
+               OpName %b "a"
+               OpName %param "b"
+               OpName %c1 "b"
+               OpName %param_0 "b"
+               OpName %FragColor "b"
+               OpDecorate %a Location 0
+               OpDecorate %b Location 1
+               OpDecorate %FragColor Location 0
+       %void = OpTypeVoid
+          %3 = OpTypeFunction %void
+      %float = OpTypeFloat 32
+    %v4float = OpTypeVector %float 4
+%_ptr_Function_v4float = OpTypePointer Function %v4float
+          %9 = OpTypeFunction %v4float %_ptr_Function_v4float
+%_ptr_Input_v4float = OpTypePointer Input %v4float
+          %a = OpVariable %_ptr_Input_v4float Input
+          %b = OpVariable %_ptr_Input_v4float Input
+%_ptr_Output_v4float = OpTypePointer Output %v4float
+  %FragColor = OpVariable %_ptr_Output_v4float Output
+       %main = OpFunction %void None %3
+          %5 = OpLabel
+         %c0 = OpVariable %_ptr_Function_v4float Function
+      %param = OpVariable %_ptr_Function_v4float Function
+         %c1 = OpVariable %_ptr_Function_v4float Function
+    %param_0 = OpVariable %_ptr_Function_v4float Function
+         %25 = OpLoad %v4float %a
+         %27 = OpLoad %v4float %b
+         %28 = OpFAdd %v4float %25 %27
+         %30 = OpLoad %v4float %a
+               OpStore %param %30
+         %31 = OpFunctionCall %v4float %func__vf4_ %param
+         %32 = OpFAdd %v4float %28 %31
+               OpStore %c0 %32
+         %34 = OpLoad %v4float %a
+         %35 = OpLoad %v4float %b
+         %36 = OpFSub %v4float %34 %35
+         %38 = OpLoad %v4float %b
+               OpStore %param_0 %38
+         %39 = OpFunctionCall %v4float %func_2_vf4_ %param_0
+         %40 = OpFAdd %v4float %36 %39
+               OpStore %c1 %40
+         %43 = OpLoad %v4float %c0
+               OpStore %FragColor %43
+         %44 = OpLoad %v4float %c1
+               OpStore %FragColor %44
+         %45 = OpLoad %v4float %c0
+               OpStore %FragColor %45
+         %46 = OpLoad %v4float %c1
+               OpStore %FragColor %46
+               OpReturn
+               OpFunctionEnd
+ %func__vf4_ = OpFunction %v4float None %9
+         %a_ = OpFunctionParameter %_ptr_Function_v4float
+         %12 = OpLabel
+         %16 = OpLoad %v4float %a_
+               OpReturnValue %16
+               OpFunctionEnd
+%func_2_vf4_ = OpFunction %v4float None %9
+        %a_2 = OpFunctionParameter %_ptr_Function_v4float
+         %15 = OpLabel
+         %19 = OpLoad %v4float %a_2
+               OpReturnValue %19
+               OpFunctionEnd

spirv_cross.cpp

@@ -998,12 +998,27 @@ void Compiler::update_name_cache(unordered_set<string> &cache, string &name)
 	uint32_t counter = 0;
 	auto tmpname = name;
 
+	bool use_linked_underscore = true;
+
+	if (tmpname == "_")
+	{
+		// We cannot just append numbers, as we will end up creating internally reserved names.
+		// Make it like _0_<counter> instead.
+		tmpname += "0";
+	}
+	else if (tmpname.back() == '_')
+	{
+		// The last_character is an underscore, so we don't need to link in underscore.
+		// This would violate double underscore rules.
+		use_linked_underscore = false;
+	}
+
 	// If there is a collision (very rare),
 	// keep tacking on extra identifier until it's unique.
 	do
 	{
 		counter++;
-		name = tmpname + "_" + convert_to_string(counter);
+		name = tmpname + (use_linked_underscore ? "_" : "") + convert_to_string(counter);
 	} while (cache.find(name) != end(cache));
 	cache.insert(name);
 }

spirv_glsl.cpp

@@ -8591,6 +8591,9 @@ void CompilerGLSL::add_variable(unordered_set<string> &variables, string &name)
 		return;
 	}
 
+	// Avoid double underscores.
+	name = sanitize_underscores(name);
+
 	update_name_cache(variables, name);
 }