Remove decoration of undefined IDs

Fix issue #185 by removing OpDecorate instructions whose target IDs are
defined in unreachable blocks and thus not dumped in the generated
SPIR-V code.

SPIRV/GlslangToSpv.cpp

@@ -719,6 +719,7 @@ void TGlslangToSpvTraverser::dumpSpv(std::vector<unsigned int>& out)
     for (auto it = iOSet.cbegin(); it != iOSet.cend(); ++it)
         entryPoint->addIdOperand(*it);
 
+    builder.eliminateDeadDecorations();
     builder.dump(out);
 }
 

SPIRV/SpvBuilder.cpp

@@ -2130,6 +2130,35 @@ Id Builder::accessChainGetInferredType()
     return type;
 }
 
+// comment in header
+void Builder::eliminateDeadDecorations() {
+    std::unordered_set<const Block*> reachable_blocks;
+    std::unordered_set<Id> unreachable_definitions;
+    // Collect IDs defined in unreachable blocks. For each function, label the
+    // reachable blocks first. Then for each unreachable block, collect the
+    // result IDs of the instructions in it.
+    for (auto& f : module.getFunctions()) {
+        Block* entry = f->getEntryBlock();
+        inReadableOrder(entry, [&reachable_blocks](const Block* b) {
+            reachable_blocks.insert(b);
+        });
+        for (auto& b : f->getBlocks()) {
+            if (!reachable_blocks.count(b)) {
+                for (auto& i : b->getInstructions()) {
+                    unreachable_definitions.insert(i->getResultId());
+                }
+            }
+        }
+    }
+    decorations.erase(std::remove_if(decorations.begin(), decorations.end(),
+        [&unreachable_definitions](std::unique_ptr<Instruction>& I) {
+            Instruction* inst = I.get();
+            Id decoration_id = inst->getIdOperand(0);
+            return unreachable_definitions.count(decoration_id) != 0;
+        }),
+        decorations.end());
+}
+
 void Builder::dump(std::vector<unsigned int>& out) const
 {
     // Header, before first instructions:

SPIRV/SpvBuilder.h

@@ -512,6 +512,9 @@ public:
     // based on the type of the base and the chain of dereferences.
     Id accessChainGetInferredType();
 
+    // Remove OpDecorate instructions whose operands are defined in unreachable
+    // blocks.
+    void eliminateDeadDecorations();
     void dump(std::vector<unsigned int>&) const;
 
     void createBranch(Block* block);

SPIRV/spvIR.h

@@ -182,6 +182,9 @@ public:
     void addLocalVariable(std::unique_ptr<Instruction> inst) { localVariables.push_back(std::move(inst)); }
     const std::vector<Block*>& getPredecessors() const { return predecessors; }
     const std::vector<Block*>& getSuccessors() const { return successors; }
+    const std::vector<std::unique_ptr<Instruction> >& getInstructions() const {
+        return instructions;
+    }
     void setUnreachable() { unreachable = true; }
     bool isUnreachable() const { return unreachable; }
     // Returns the block's merge instruction, if one exists (otherwise null).
@@ -275,6 +278,7 @@ public:
     Module& getParent() const { return parent; }
     Block* getEntryBlock() const { return blocks.front(); }
     Block* getLastBlock() const { return blocks.back(); }
+    const std::vector<Block*>& getBlocks() const { return blocks; }
     void addLocalVariable(std::unique_ptr<Instruction> inst);
     Id getReturnType() const { return functionInstruction.getTypeId(); }
     void dump(std::vector<unsigned int>& out) const
@@ -326,6 +330,7 @@ public:
     }
 
     Instruction* getInstruction(Id id) const { return idToInstruction[id]; }
+    const std::vector<Function*>& getFunctions() const { return functions; }
     spv::Id getTypeId(Id resultId) const { return idToInstruction[resultId]->getTypeId(); }
     StorageClass getStorageClass(Id typeId) const
     {