Avoid out of range access to spirv data.

Avoids debug assertion crashes on MSVC 2015 when trying to access
elements out of range.

spirv_cross.cpp

@@ -60,7 +60,7 @@ bool Compiler::block_is_pure(const SPIRBlock &block)
 {
     for (auto &i : block.ops)
     {
-        auto ops = stream(i.offset);
+        auto ops = stream(i);
         auto op = static_cast<Op>(i.op);
 
         switch (op)
@@ -119,7 +119,7 @@ void Compiler::register_global_read_dependencies(const SPIRBlock &block, uint32_
 {
     for (auto &i : block.ops)
     {
-        auto ops = stream(i.offset);
+        auto ops = stream(i);
         auto op = static_cast<Op>(i.op);
 
         switch (op)
@@ -443,11 +443,11 @@ static string extract_string(const vector<uint32_t> &spirv, uint32_t offset)
 void Compiler::parse()
 {
     auto len = spirv.size();
-    auto s = stream(0);
-
     if (len < 5)
         throw CompilerError("SPIRV file too small.");
 
+    auto s = spirv.data();
+
     // Endian-swap if we need to.
     if (s[0] == swap_endian(MagicNumber))
         transform(begin(spirv), end(spirv), begin(spirv), [](uint32_t c) { return swap_endian(c); });
@@ -778,7 +778,7 @@ void Compiler::unset_decoration(uint32_t id, Decoration decoration)
 
 void Compiler::parse(const Instruction &i)
 {
-    auto ops = stream(i.offset);
+    auto ops = stream(i);
     auto op = static_cast<Op>(i.op);
     uint32_t length = i.length;
 
@@ -1651,7 +1651,7 @@ bool Compiler::traverse_all_reachable_opcodes(const SPIRBlock &block, OpcodeHand
     // inside dead blocks ...
     for (auto &i : block.ops)
     {
-        auto ops = stream(i.offset);
+        auto ops = stream(i);
         auto op = static_cast<Op>(i.op);
 
         if (!handler.handle(op, ops, i.length))

spirv_cross.hpp

@@ -168,11 +168,17 @@ namespace spirv_cross
             ShaderResources get_shader_resources() const;
 
         protected:
-            const uint32_t* stream(uint32_t offset) const
+            const uint32_t* stream(const Instruction &instr) const
             {
-                if (offset > spirv.size())
+                // If we're not going to use any arguments, just return nullptr.
+                // We want to avoid case where we return an out of range pointer
+                // that trips debug assertions on some platforms.
+                if (!instr.length)
+                    return nullptr;
+
+                if (instr.offset + instr.length > spirv.size())
                     throw CompilerError("Compiler::stream() out of range.");
-                return &spirv[offset];
+                return &spirv[instr.offset];
             }
             std::vector<uint32_t> spirv;
 

spirv_glsl.cpp

@@ -1353,7 +1353,7 @@ void CompilerGLSL::emit_mix_op(uint32_t result_type, uint32_t id,
 
 void CompilerGLSL::emit_texture_op(const Instruction &i)
 {
-    auto ops = stream(i.offset);
+    auto ops = stream(i);
     auto op = static_cast<Op>(i.op);
     uint32_t length = i.length;
 
@@ -2274,7 +2274,7 @@ string CompilerGLSL::build_composite_combiner(const uint32_t *elems, uint32_t le
 
 void CompilerGLSL::emit_instruction(const Instruction &i)
 {
-    auto ops = stream(i.offset);
+    auto ops = stream(i);
     auto op = static_cast<Op>(i.op);
     uint32_t length = i.length;
 
@@ -3615,7 +3615,7 @@ void CompilerGLSL::emit_function(SPIRFunction &func, uint64_t return_flags)
         auto &b = get<SPIRBlock>(block);
         for (auto &i : b.ops)
         {
-            auto ops = stream(i.offset);
+            auto ops = stream(i);
             auto op = static_cast<Op>(i.op);
 
             if (op == OpFunctionCall)