Vulkan: Avoid OpKill workaround with no stencil.

It seems like depth gets messed up either way on discard, but behaves
sorta better without the write to depth.

GPU/Common/ShaderId.cpp

@@ -201,8 +201,10 @@ std::string FragmentShaderDesc(const ShaderID &id) {
 		case STENCIL_VALUE_INCR_8: desc << "StenIncr8 "; break;
 		case STENCIL_VALUE_DECR_4: desc << "StenDecr4 "; break;
 		case STENCIL_VALUE_DECR_8: desc << "StenDecr4 "; break;
-		default: desc << "StenUnknown"; break;
+		default: desc << "StenUnknown "; break;
 		}
+	} else if (id.Bit(FS_BIT_REPLACE_ALPHA_WITH_STENCIL_TYPE)) {
+		desc << "StenOff ";
 	}
 	if (id.Bit(FS_BIT_DO_TEXTURE)) {
 		switch (id.Bits(FS_BIT_TEXFUNC, 3)) {
@@ -292,6 +294,9 @@ void ComputeFragmentShaderID(ShaderID *id_out) {
 		if (stencilToAlpha != REPLACE_ALPHA_NO) {
 			// 4 bits
 			id.SetBits(FS_BIT_REPLACE_ALPHA_WITH_STENCIL_TYPE, 4, ReplaceAlphaWithStencilType());
+		} else {
+			// Use those bits instead for whether stencil output is disabled.
+			id.SetBit(FS_BIT_REPLACE_ALPHA_WITH_STENCIL_TYPE, IsStencilTestOutputDisabled());
 		}
 
 		// 2 bits.

GPU/Vulkan/FragmentShaderGeneratorVulkan.cpp

@@ -84,12 +84,13 @@ bool GenerateVulkanGLSLFragmentShader(const FShaderID &id, char *buffer, uint32_
 
 	const char *shading = doFlatShading ? "flat" : "";
 	bool earlyFragmentTests = ((!enableAlphaTest && !enableColorTest) || testForceToZero) && !gstate_c.Supports(GPU_ROUND_FRAGMENT_DEPTH_TO_16BIT);
+	bool hasStencilOutput = stencilToAlpha != REPLACE_ALPHA_NO || id.Bit(FS_BIT_REPLACE_ALPHA_WITH_STENCIL_TYPE) == 0;
 
 	bool isAdreno = vulkanVendorId == VULKAN_VENDOR_QUALCOMM;
 
 	if (earlyFragmentTests) {
 		WRITE(p, "layout (early_fragment_tests) in;\n");
-	} else if (isAdreno) {
+	} else if (isAdreno && hasStencilOutput && !gstate_c.Supports(GPU_ROUND_FRAGMENT_DEPTH_TO_16BIT)) {
 		WRITE(p, "layout (depth_unchanged) out float gl_FragDepth;\n");
 	}
 
@@ -585,7 +586,7 @@ bool GenerateVulkanGLSLFragmentShader(const FShaderID &id, char *buffer, uint32_
 			WRITE(p, "  z = (1.0/65535.0) * floor(z * 65535.0);\n");
 		}
 		WRITE(p, "  gl_FragDepth = z;\n");
-	} else if (!earlyFragmentTests && isAdreno) {
+	} else if (!earlyFragmentTests && isAdreno && hasStencilOutput) {
 		// Adreno (and possibly MESA/others) apply early frag tests even with discard in the shader.
 		// Writing depth prevents the bug, even with depth_unchanged specified.
 		WRITE(p, "  gl_FragDepth = gl_FragCoord.z;\n");