Fix for global generic parameter substitution (#512)

The problem here arises when multiple entry points are compiled in one pass. Each entry point has its own arguments for global generic parameters, and leads to us emitting a `bindGlobalGenericParameter(p, val)`. But once the first entry point's substitutions are applied, the second entry point's code gives `bindGlobalGenericParameter(val, val)` and the compiler crashes (in debug builds) because `val` is not a global generic parameter.

This change just applies a quick fix. If we see `bindGlobalGenericParameter(x,y)` during specialization, and `x` is not a global generic parameter, then we skip it.

The right long-term fix is to change the compiler's representation of global generic arguments so that they live on a `CompileRequest` instead of an `EntryPointRequest`. That is a more significant change (with impact on the public API), so I'm inclined to leave it as a cleanup for another day (given that no customers are using global generic parameters today).

1 files changed, 14 insertions, 0 deletions

diff --git a/source/slang/ir.cpp b/source/slang/ir.cpp
index 2b0e19a0c..a4a118250 100644
--- a/source/slang/ir.cpp
+++ b/source/slang/ir.cpp
@@ -6252,6 +6252,20 @@ namespace Slang
             if(!bindInst)
                 continue;
 
+            // HACK: Our current front-end emit logic can end up emitting multiple
+            // `bindGlobalGeneric` instructions for the same parameter. This is
+            // a buggy behavior, but a real fix would require refactoring the way
+            // global generic arguments are specified today.
+            //
+            // For now we will do a sanity check to detect parameters that
+            // have already been specialized.
+            if( !as<IRGlobalGenericParam>(bindInst->getOperand(0)) )
+            {
+                // parameter operand is no longer a parameter, so it
+                // seems things must have been specialized already.
+                continue;
+            }
+
             auto param = bindInst->getParam();
             auto val = bindInst->getVal();