Merge pull request #1686 from KhronosGroup/fix-1684

GLSL: Support control flow hints

1 files changed, 46 insertions, 2 deletions

diff --git a/spirv_glsl.cpp b/spirv_glsl.cpp
index 99f42638..bde261eb 100644
--- a/spirv_glsl.cpp
+++ b/spirv_glsl.cpp
@@ -823,6 +823,22 @@ void CompilerGLSL::emit_header()
 			statement("#extension ", ext, " : enable");
 			statement("#endif");
 		}
+		else if (ext == "GL_EXT_control_flow_attributes")
+		{
+			// These are just hints so we can conditionally enable and fallback in the shader.
+			statement("#if defined(GL_EXT_control_flow_attributes)");
+			statement("#extension GL_EXT_control_flow_attributes : require");
+			statement("#define SPIRV_CROSS_FLATTEN [[flatten]]");
+			statement("#define SPIRV_CROSS_BRANCH [[dont_flatten]]");
+			statement("#define SPIRV_CROSS_UNROLL [[unroll]]");
+			statement("#define SPIRV_CROSS_LOOP [[dont_unroll]]");
+			statement("#else");
+			statement("#define SPIRV_CROSS_FLATTEN");
+			statement("#define SPIRV_CROSS_BRANCH");
+			statement("#define SPIRV_CROSS_UNROLL");
+			statement("#define SPIRV_CROSS_LOOP");
+			statement("#endif");
+		}
 		else
 			statement("#extension ", ext, " : require");
 	}
@@ -14004,7 +14020,10 @@ void CompilerGLSL::branch(BlockID from, uint32_t cond, BlockID true_block, Block
 	if (!true_block_needs_code && !false_block_needs_code)
 		return;
 
-	emit_block_hints(get<SPIRBlock>(from));
+	// We might have a loop merge here. Only consider selection flattening constructs.
+	// Loop hints are handled explicitly elsewhere.
+	if (from_block.hint == SPIRBlock::HintFlatten || from_block.hint == SPIRBlock::HintDontFlatten)
+		emit_block_hints(from_block);
 
 	if (true_block_needs_code)
 	{
@@ -14510,6 +14529,7 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 		// for (;;) { create-temporary; break; } consume-temporary;
 		// so force-declare temporaries here.
 		emit_hoisted_temporaries(block.potential_declare_temporary);
+		emit_block_hints(block);
 		statement("for (;;)");
 		begin_scope();
 
@@ -15376,8 +15396,32 @@ void CompilerGLSL::convert_non_uniform_expression(string &expr, uint32_t ptr_id)
 	            expr.substr(end_array_index, string::npos));
 }
 
-void CompilerGLSL::emit_block_hints(const SPIRBlock &)
+void CompilerGLSL::emit_block_hints(const SPIRBlock &block)
 {
+	if ((options.es && options.version < 310) || (!options.es && options.version < 140))
+		return;
+
+	switch (block.hint)
+	{
+	case SPIRBlock::HintFlatten:
+		require_extension_internal("GL_EXT_control_flow_attributes");
+		statement("SPIRV_CROSS_FLATTEN");
+		break;
+	case SPIRBlock::HintDontFlatten:
+		require_extension_internal("GL_EXT_control_flow_attributes");
+		statement("SPIRV_CROSS_BRANCH");
+		break;
+	case SPIRBlock::HintUnroll:
+		require_extension_internal("GL_EXT_control_flow_attributes");
+		statement("SPIRV_CROSS_UNROLL");
+		break;
+	case SPIRBlock::HintDontUnroll:
+		require_extension_internal("GL_EXT_control_flow_attributes");
+		statement("SPIRV_CROSS_LOOP");
+		break;
+	default:
+		break;
+	}
 }
 
 void CompilerGLSL::preserve_alias_on_reset(uint32_t id)