Warn when inout parameter is never written (#4777)

Addresses #4698 as one approach to diagnose the potential problem.

Emit warnings when a user marks a parameter as `inout` but never writes to it in the function. A new intrinsic function `unmodified(out T)` has been added to explicitly indicate that an `inout` variable will not be modified in the function.

This is only one way to address the specific validation error in #4698. In general it seems that DXC does some more extensive checks on actual struct fields (as opposed to observing arbitrary struct writes), so that will be the next step.

1 files changed, 1 insertions, 0 deletions

diff --git a/source/slang/slang-emit-spirv.cpp b/source/slang/slang-emit-spirv.cpp
index 23eaa4435..bb0a2565c 100644
--- a/source/slang/slang-emit-spirv.cpp
+++ b/source/slang/slang-emit-spirv.cpp
@@ -2719,6 +2719,7 @@ struct SPIRVEmitContext
         case kIROp_Specialize:
         case kIROp_MissingReturn:
         case kIROp_StaticAssert:
+        case kIROp_Unmodified:
             break;
         case kIROp_Var:
             result = emitVar(parent, inst);