Add intrinsic for `IsHelperLane()` in HLSL (#4471)

Add InHelperLane() intrinsic for HLSL, GLSL, Metal and Spirv.

2 files changed, 23 insertions, 0 deletions

diff --git a/source/slang/hlsl.meta.slang b/source/slang/hlsl.meta.slang
index c01265369..82ef5837e 100644
--- a/source/slang/hlsl.meta.slang
+++ b/source/slang/hlsl.meta.slang
@@ -14949,6 +14949,24 @@ matrix<T,N,M> WaveMultiPrefixSum(matrix<T,N,M> value, uint4 mask)
     }
 }
 
+__glsl_extension(GL_EXT_demote_to_helper_invocation)
+[ForceInline]
+[require(glsl_hlsl_metal_spirv, helper_lane)]
+bool IsHelperLane()
+{
+    __target_switch {
+    case hlsl: __intrinsic_asm "IsHelperLane()";
+    case glsl: __intrinsic_asm "gl_HelperInvocation";
+    case metal: __intrinsic_asm "simd_is_helper_thread()";
+    case spirv:
+        return spirv_asm {
+            OpExtension "SPV_EXT_demote_to_helper_invocation";
+            OpCapability DemoteToHelperInvocationEXT;
+            result:$$bool = OpIsHelperInvocationEXT
+        };
+    }
+}
+
 // `typedef`s to help with the fact that HLSL has been sorta-kinda case insensitive at various points
 typedef Texture2D texture2D;
 
diff --git a/source/slang/slang-capabilities.capdef b/source/slang/slang-capabilities.capdef
index d003e4f41..b011021bc 100644
--- a/source/slang/slang-capabilities.capdef
+++ b/source/slang/slang-capabilities.capdef
@@ -817,6 +817,11 @@ alias atomic_glsl_hlsl_nvapi_cuda9_int64 = atomic_glsl_int64 | hlsl_nvapi + _sm_
 alias atomic_glsl_hlsl_cuda = atomic_glsl | _sm_5_0 | _cuda_sm_2_0;
 alias atomic_glsl_hlsl_cuda9_int64 = atomic_glsl_int64 | _sm_6_6 | _cuda_sm_9_0;
 
+alias helper_lane = _sm_6_0 + fragment
+                   | GL_EXT_demote_to_helper_invocation + fragment
+                   | metal + fragment
+                   ;
+
 alias breakpoint = GL_EXT_debug_printf | hlsl | _cuda_sm_8_0 | cpp;
 
 alias raytracing_allstages = raytracing_stages + raytracing;