commit ebb505355d59f61dfc9547f81e14b2d9cd1eb2f0
author John Kessenich <cepheus@frii.com> Mon May 16 19:22:05 2016 -0600
committer John Kessenich <cepheus@frii.com> Mon May 16 19:32:59 2016 -0600
tree 915552c9f6302fa68cfb146d329194673c122f17
parent e5f29393da1c624e22b7bde9b51d5f3678d73859

SPV: Don't add clip/cull distance capabilities unless used.

These capabalities were added on declaration of the members, but
that is considered too aggressive, as those members are automatically
declared in some shaders that don't use them.  Now, actual access
is needed to make the capabalities be declared.

SPIRV/GlslangToSpv.cpp

diff --git a/SPIRV/GlslangToSpv.cpp b/SPIRV/GlslangToSpv.cpp
index 2b76c04..92d20f8 100755
--- a/SPIRV/GlslangToSpv.cpp
+++ b/SPIRV/GlslangToSpv.cpp
@@ -109,7 +109,7 @@
 
 protected:
     spv::Decoration TranslateInterpolationDecoration(const glslang::TQualifier& qualifier);
-    spv::BuiltIn TranslateBuiltInDecoration(glslang::TBuiltInVariable);
+    spv::BuiltIn TranslateBuiltInDecoration(glslang::TBuiltInVariable, bool member);
     spv::ImageFormat TranslateImageFormat(const glslang::TType& type);
     spv::Id createSpvVariable(const glslang::TIntermSymbol*);
     spv::Id getSampledType(const glslang::TSampler&);
@@ -122,6 +122,7 @@
     int getArrayStride(const glslang::TType& arrayType, glslang::TLayoutPacking, glslang::TLayoutMatrix);
     int getMatrixStride(const glslang::TType& matrixType, glslang::TLayoutPacking, glslang::TLayoutMatrix);
     void updateMemberOffset(const glslang::TType& structType, const glslang::TType& memberType, int& currentOffset, int& nextOffset, glslang::TLayoutPacking, glslang::TLayoutMatrix);
+    void declareClipCullCapability(const glslang::TTypeList& members, int member);
 
     bool isShaderEntrypoint(const glslang::TIntermAggregate* node);
     void makeFunctions(const glslang::TIntermSequence&);
@@ -393,7 +394,7 @@
 }
 
 // Translate glslang built-in variable to SPIR-V built in decoration.
-spv::BuiltIn TGlslangToSpvTraverser::TranslateBuiltInDecoration(glslang::TBuiltInVariable builtIn)
+spv::BuiltIn TGlslangToSpvTraverser::TranslateBuiltInDecoration(glslang::TBuiltInVariable builtIn, bool member)
 {
     switch (builtIn) {
     case glslang::EbvPointSize:
@@ -410,12 +411,20 @@
         }
         return spv::BuiltInPointSize;
 
+    // These *Distance capabilities logically belong here, but if the member is declared and
+    // then never used, consumers of SPIR-V prefer the capability not be declared.
+    // They are now generated when used, rather than here when declared.
+    // Potentially, the specification should be more clear what the minimum
+    // use needed is to trigger the capability.
+    //
     case glslang::EbvClipDistance:
-        builder.addCapability(spv::CapabilityClipDistance);
+        if (! member)
+            builder.addCapability(spv::CapabilityClipDistance);
         return spv::BuiltInClipDistance;
 
     case glslang::EbvCullDistance:
-        builder.addCapability(spv::CapabilityCullDistance);
+        if (! member)
+            builder.addCapability(spv::CapabilityCullDistance);
         return spv::BuiltInCullDistance;
 
     case glslang::EbvViewportIndex:
@@ -926,6 +935,10 @@
             } else {
                 // normal case for indexing array or structure or block
                 builder.accessChainPush(builder.makeIntConstant(index));
+
+                // Add capabilities here for accessing clip/cull distance
+                if (node->getLeft()->getType().isStruct() && ! node->getLeft()->getType().isArray())
+                    declareClipCullCapability(*node->getLeft()->getType().getStruct(), index);
             }
         }
         return false;
@@ -1919,7 +1932,7 @@
                         builder.addMemberDecoration(spvType, member, spv::DecorationMatrixStride, getMatrixStride(glslangType, explicitLayout, subQualifier.layoutMatrix));
 
                     // built-in variable decorations
-                    spv::BuiltIn builtIn = TranslateBuiltInDecoration(glslangType.getQualifier().builtIn);
+                    spv::BuiltIn builtIn = TranslateBuiltInDecoration(glslangType.getQualifier().builtIn, true);
                     if (builtIn != spv::BadValue)
                         addMemberDecoration(spvType, member, spv::DecorationBuiltIn, (int)builtIn);
                 }
@@ -2172,6 +2185,14 @@
     nextOffset = currentOffset + memberSize;
 }
 
+void TGlslangToSpvTraverser::declareClipCullCapability(const glslang::TTypeList& members, int member)
+{
+    if (members[member].type->getQualifier().builtIn == glslang::EbvClipDistance)
+        builder.addCapability(spv::CapabilityClipDistance);
+    if (members[member].type->getQualifier().builtIn == glslang::EbvCullDistance)
+        builder.addCapability(spv::CapabilityCullDistance);
+}
+
 bool TGlslangToSpvTraverser::isShaderEntrypoint(const glslang::TIntermAggregate* node)
 {
     // have to ignore mangling and just look at the base name
@@ -3936,7 +3957,7 @@
     }
 
     // built-in variable decorations
-    spv::BuiltIn builtIn = TranslateBuiltInDecoration(symbol->getQualifier().builtIn);
+    spv::BuiltIn builtIn = TranslateBuiltInDecoration(symbol->getQualifier().builtIn, false);
     if (builtIn != spv::BadValue)
         addDecoration(id, spv::DecorationBuiltIn, (int)builtIn);