HLSL: implement [unroll] and [loop] attributes

This adds infrastructure suitable for any front end to create SPIR-V loop
control flags.  The only current front end doing so is HLSL.

[unroll] turns into spv::LoopControlUnrollMask
[loop] turns into spv::LoopControlDontUnrollMask
no specification means spv::LoopControlMaskNone

hlsl/hlslAttributes.cpp

@@ -80,6 +80,8 @@ namespace glslang {
             return EatPatchConstantFunc;
         else if (lowername == "unroll")
             return EatUnroll;
+        else if (lowername == "loop")
+            return EatLoop;
         else
             return EatNone;
     }
@@ -107,4 +109,10 @@ namespace glslang {
         return (entry == attributes.end()) ? nullptr : entry->second;
     }
 
+    // True if entry exists in map (even if value is nullptr)
+    bool TAttributeMap::contains(TAttributeType attr) const
+    {
+        return attributes.find(attr) != attributes.end();
+    }
+
 } // end namespace glslang

hlsl/hlslAttributes.h

@@ -62,6 +62,7 @@ namespace glslang {
         EatPatchConstantFunc,
         EatPatchSize,
         EatUnroll,
+        EatLoop,
     };
 }
 
@@ -86,6 +87,9 @@ namespace glslang {
         // Const lookup: search for (but do not modify) the attribute in the map.
         const TIntermAggregate* operator[](TAttributeType) const;
 
+        // True if entry exists in map (even if value is nullptr)
+        bool contains(TAttributeType) const;
+
     protected:
         // Find an attribute enum given its name.
         static TAttributeType attributeFromName(const TString&);

hlsl/hlslGrammar.cpp

@@ -3127,7 +3127,7 @@ bool HlslGrammar::acceptStatement(TIntermNode*& statement)
     case EHTokFor:
     case EHTokDo:
     case EHTokWhile:
-        return acceptIterationStatement(statement);
+        return acceptIterationStatement(statement, attributes);
 
     case EHTokContinue:
     case EHTokBreak:
@@ -3336,7 +3336,7 @@ bool HlslGrammar::acceptSwitchStatement(TIntermNode*& statement)
 //      | FOR LEFT_PAREN for_init_statement for_rest_statement RIGHT_PAREN statement
 //
 // Non-speculative, only call if it needs to be found; WHILE or DO or FOR already seen.
-bool HlslGrammar::acceptIterationStatement(TIntermNode*& statement)
+bool HlslGrammar::acceptIterationStatement(TIntermNode*& statement, const TAttributeMap& attributes)
 {
     TSourceLoc loc = token.loc;
     TIntermTyped* condition = nullptr;
@@ -3346,6 +3346,8 @@ bool HlslGrammar::acceptIterationStatement(TIntermNode*& statement)
 
     //  WHILE or DO or FOR
     advanceToken();
+    
+    const TLoopControl control = parseContext.handleLoopControl(attributes);
 
     switch (loop) {
     case EHTokWhile:
@@ -3370,7 +3372,7 @@ bool HlslGrammar::acceptIterationStatement(TIntermNode*& statement)
         parseContext.unnestLooping();
         parseContext.popScope();
 
-        statement = intermediate.addLoop(statement, condition, nullptr, true, loc);
+        statement = intermediate.addLoop(statement, condition, nullptr, true, loc, control);
 
         return true;
 
@@ -3402,7 +3404,7 @@ bool HlslGrammar::acceptIterationStatement(TIntermNode*& statement)
 
         parseContext.unnestLooping();
 
-        statement = intermediate.addLoop(statement, condition, 0, false, loc);
+        statement = intermediate.addLoop(statement, condition, 0, false, loc, control);
 
         return true;
 
@@ -3451,7 +3453,7 @@ bool HlslGrammar::acceptIterationStatement(TIntermNode*& statement)
             return false;
         }
 
-        statement = intermediate.addForLoop(statement, initNode, condition, iterator, true, loc);
+        statement = intermediate.addForLoop(statement, initNode, condition, iterator, true, loc, control);
 
         parseContext.popScope();
         parseContext.unnestLooping();

hlsl/hlslGrammar.h

@@ -116,7 +116,7 @@ namespace glslang {
         void acceptAttributes(TAttributeMap&);
         bool acceptSelectionStatement(TIntermNode*&);
         bool acceptSwitchStatement(TIntermNode*&);
-        bool acceptIterationStatement(TIntermNode*&);
+        bool acceptIterationStatement(TIntermNode*&, const TAttributeMap&);
         bool acceptJumpStatement(TIntermNode*&);
         bool acceptCaseLabel(TIntermNode*&);
         bool acceptDefaultLabel(TIntermNode*&);

hlsl/hlslParseHelper.cpp

@@ -7568,6 +7568,20 @@ bool HlslParseContext::handleOutputGeometry(const TSourceLoc& loc, const TLayout
     return true;
 }
 
+//
+// Loop hints
+//
+TLoopControl HlslParseContext::handleLoopControl(const TAttributeMap& attributes) const
+{
+    if (attributes.contains(EatUnroll))
+        return ELoopControlUnroll;
+    else if (attributes.contains(EatLoop))
+        return ELoopControlDontUnroll;
+    else
+        return ELoopControlNone;
+}
+
+
 //
 // Updating default qualifier for the case of a declaration with just a qualifier,
 // no type, block, or identifier.

hlsl/hlslParseHelper.h

@@ -192,6 +192,9 @@ public:
     bool handleOutputGeometry(const TSourceLoc&, const TLayoutGeometry& geometry);
     bool handleInputGeometry(const TSourceLoc&, const TLayoutGeometry& geometry);
 
+    // Determine loop control from attributes
+    TLoopControl handleLoopControl(const TAttributeMap& attributes) const;
+
     // Potentially rename shader entry point function
     void renameShaderFunction(const TString*& name) const;