Support for `[[vk::spirv_instruction(op)]]` (#2242)

* #include an absolute path didn't work - because paths were taken to always be relative.

* Add extension required by SPIRVOpDecoration into part of emit (could be a prior pass).

* Add [[vk::spirv_instruction]] attribute

* Add documentation for [[vk::spirv_instruction].

* Update 08-attributes.md

* Update 08-attributes.md

9 files changed, 70 insertions, 6 deletions

diff --git a/docs/language-reference/08-attributes.md b/docs/language-reference/08-attributes.md
index 4098303cf..76a739315 100644
--- a/docs/language-reference/08-attributes.md
+++ b/docs/language-reference/08-attributes.md
@@ -2,3 +2,29 @@ Attributes
 ==========
 
 > Note: This section is not yet complete.
+
+## [[vk::spirv_instruction]]
+
+** SPIR-V only **
+
+This attribute is only available for Vulkan SPIR-V output via GLSLANG. In the future it could be supported via the `direct-spirv` option. The attribute will be ignored for any other target. This attribute requires the `GL_EXT_spirv_intrinsics` GLSL extension.
+
+The attibute allows access to SPIR-V intrinsics, by supplying a function declaration with the appropriate signature for the SPIR-V op and no body. The intrinsic takes a single parameter which is the integer value for the SPIR-V op. 
+
+In the example below the add function, uses the mechanism to directly use the SPIR-V integer add 'op' which is 128 in this case.
+
+```HLSL
+// 128 is OpIAdd in SPIR-V
+[[vk::spirv_instruction(128)]]
+uint add(uint a, uint b);
+
+RWStructuredBuffer<uint> resultBuffer;
+
+[numthreads(4,1,1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    uint threadId = dispatchThreadID.x;
+    resultBuffer[threadId] = add(threadId, threadId);
+}
+```
+
diff --git a/source/slang/core.meta.slang b/source/slang/core.meta.slang
index 9a09196c5..476e88e3f 100644
--- a/source/slang/core.meta.slang
+++ b/source/slang/core.meta.slang
@@ -2059,6 +2059,9 @@ attribute_syntax [vk_location(locaiton : int)] : GLSLLocationAttribute;
 __attributeTarget(VarDeclBase)
 attribute_syntax [vk_index(index : int)] : GLSLIndexAttribute;
 
+__attributeTarget(FuncDecl)
+attribute_syntax [vk_spirv_instruction(op : int)]                   : SPIRVInstructionOpAttribute;
+
 // Statement Attributes
 
 __attributeTarget(LoopStmt)
diff --git a/source/slang/slang-ast-modifier.h b/source/slang/slang-ast-modifier.h
index a8185e06e..4522b7148 100644
--- a/source/slang/slang-ast-modifier.h
+++ b/source/slang/slang-ast-modifier.h
@@ -671,6 +671,11 @@ class GLSLIndexAttribute : public GLSLSimpleIntegerLayoutAttribute
     SLANG_AST_CLASS(GLSLIndexAttribute)
 };
 
+// [[vk_spirv_instruction]]
+class SPIRVInstructionOpAttribute : public Attribute
+{
+    SLANG_AST_CLASS(SPIRVInstructionOpAttribute)
+};
 
 // TODO: for attributes that take arguments, the syntax node
 // classes should provide accessors for the values of those arguments.
diff --git a/source/slang/slang-check-modifier.cpp b/source/slang/slang-check-modifier.cpp
index 320b980e9..1d9e30c95 100644
--- a/source/slang/slang-check-modifier.cpp
+++ b/source/slang/slang-check-modifier.cpp
@@ -398,7 +398,8 @@ namespace Slang
                 getSink()->diagnose(attr, Diagnostics::expectedSingleStringArg, attr->keywordName);
             }
         }
-        else if (as<OutputControlPointsAttribute>(attr))
+        else if (as<OutputControlPointsAttribute>(attr) ||
+                    as<SPIRVInstructionOpAttribute>(attr))
         {
             // Let it go thru iff single integral attribute
             if (!hasIntArgs(attr, 1))
diff --git a/source/slang/slang-emit-glsl.cpp b/source/slang/slang-emit-glsl.cpp
index d9c81f14b..c1bbf813b 100644
--- a/source/slang/slang-emit-glsl.cpp
+++ b/source/slang/slang-emit-glsl.cpp
@@ -1881,6 +1881,8 @@ void GLSLSourceEmitter::emitFuncDecorationImpl(IRDecoration* decoration)
 {
     if (decoration->getOp() == kIROp_SPIRVOpDecoration)
     {
+        m_glslExtensionTracker->requireExtension(UnownedStringSlice::fromLiteral("GL_EXT_spirv_intrinsics"));
+
         m_writer->emit("spirv_instruction(id = ");
         emitSimpleValue(decoration->getOperand(0));
         m_writer->emit(")\n");
diff --git a/source/slang/slang-ir-glsl-liveness.cpp b/source/slang/slang-ir-glsl-liveness.cpp
index 3cfde0246..d5448a788 100644
--- a/source/slang/slang-ir-glsl-liveness.cpp
+++ b/source/slang/slang-ir-glsl-liveness.cpp
@@ -60,7 +60,6 @@ struct GLSLLivenessContext
 
     Entry m_entries[Index(Kind::CountOf)];          /// Entry for each kind of function
 
-    IRStringLit* m_extensionStringLiteral = nullptr;        ///< The string literal holding the SPIR-V extension needed 
     IRInst* m_zeroIntLiteral = nullptr;                     ///< Zero value literal
     IRType* m_spirvIntLiteralType = nullptr;                ///< Int type that emits as `spirv_literal`
 
@@ -92,9 +91,8 @@ void GLSLLivenessContext::_addDecorations(Kind kind, IRFunc* func)
     //
     // m_builder.addTargetDecoration();
 
-    // We need the spirv extension
-    m_builder.addDecoration(func, kIROp_RequireGLSLExtensionDecoration, m_extensionStringLiteral);
-
+    // We don't need to explictly add the "GL_EXT_spirv_intrinsics"
+    // as it will be added on the GLSL emit, with the SPIRVOpDecoration is hit
     const auto& entry = m_entries[Index(kind)];
     if (entry.m_nameHintLiteral)
     {
@@ -207,8 +205,10 @@ void GLSLLivenessContext::processModule()
     // Zero value literal
     m_zeroIntLiteral = m_builder.getIntValue(m_builder.getIntType(), 0);
 
+    // We don't need to explicitly add this decoration because it will be added as needed on GLSL emit
+    // m_extensionStringLiteral = m_builder.getStringValue(UnownedStringSlice::fromLiteral("GL_EXT_spirv_intrinsics"));
+
     // Set up some values that will be needed on instructions
-    m_extensionStringLiteral = m_builder.getStringValue(UnownedStringSlice::fromLiteral("GL_EXT_spirv_intrinsics"));
 
     // The op values are from the SPIR-V spec
     // https://www.khronos.org/registry/SPIR-V/specs/unified1/SPIRV.html#OpLifetimeStart
diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index 585b02a02..4ff43b697 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -7517,6 +7517,12 @@ struct DeclLoweringVisitor : DeclVisitor<DeclLoweringVisitor, LoweredValInfo>
             getBuilder()->addDecoration(irFunc, kIROp_OutputControlPointsDecoration, intLit);
         }
 
+        if (auto attr = decl->findModifier<SPIRVInstructionOpAttribute>())
+        {
+            IRIntLit* intLit = _getIntLitFromAttribute(getBuilder(), attr);
+            getBuilder()->addDecoration(irFunc, kIROp_SPIRVOpDecoration, intLit);
+        }
+
         if(decl->findModifier<UnsafeForceInlineEarlyAttribute>())
         {
             getBuilder()->addDecoration(irFunc, kIROp_UnsafeForceInlineEarlyDecoration);
diff --git a/tests/spirv/spirv-instruction.slang b/tests/spirv/spirv-instruction.slang
new file mode 100644
index 000000000..1f85479f9
--- /dev/null
+++ b/tests/spirv/spirv-instruction.slang
@@ -0,0 +1,17 @@
+// spirv-instruction.slang
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute 
+
+// Test using a spirv op. 128 is SpvOpIAdd
+
+[[vk::spirv_instruction(128)]]
+uint add(uint a, uint b);
+
+//TEST_INPUT:set resultBuffer = out ubuffer(data=[0 0 0 0], stride=4)
+RWStructuredBuffer<uint> resultBuffer;
+
+[numthreads(4,1,1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    uint threadId = dispatchThreadID.x;
+    resultBuffer[threadId] = add(threadId, threadId);
+}
diff --git a/tests/spirv/spirv-instruction.slang.expected.txt b/tests/spirv/spirv-instruction.slang.expected.txt
new file mode 100644
index 000000000..e1e8ccec4
--- /dev/null
+++ b/tests/spirv/spirv-instruction.slang.expected.txt
@@ -0,0 +1,4 @@
+0
+2
+4
+6