From d61d6b57dfb0788ebf3449bfde6db288fe4e44a8 Mon Sep 17 00:00:00 2001
From: Gangzheng Tong <tonggangzheng@gmail.com>
Date: Tue, 23 Sep 2025 09:39:39 -0700
Subject: Legalize type as well in legalizeOperand (#8483)
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This fixes a type mismatch issue. See the generated cuda code

```cuda
struct Query_0
{
    EmptyExample_0 query_0;
    uint hasNonEmptyAbsorbingBoundary_0;
};

struct Query_1
{
    uint hasNonEmptyAbsorbingBoundary_0;
};

struct GlobalParams_0
{
    Query_0* gQuery_0;
    RWStructuredBuffer<float3 > gInput_0;
    RWStructuredBuffer<float> gOutput_0;
};

...
Query_1 _S4 = *globalParams_0->gQuery_0;      // ==> type mismatch at call site!

```

**Root Cause:** During the empty type legalization pass in Slang's IR
processing, struct types were being optimized. e.g., `Query_0` →
`Query_1` with empty type removed), but this created an inconsistency:

**Function parameters were updated:** When Query_compute_0 function was
legalized, its parameter type was correctly updated from `Query_0` to
the optimized `Query_1`

**Global parameter types were NOT updated:** The
`ParameterBlock<Struct>` type in globalParams still referenced the old
`Query_0` type

The PR adds special handling for type operands in the `legalizeInst`
function. This triggers the legalization of the `StructType` from the
original `legalizeOperand` call site. The leaglized result will be saved
in the type-to-legal-type map and be re-used when the same type requires
legalization again (e.g. in the `IRFunc` as parameter)

Fixes: https://github.com/shader-slang/slang/issues/7905
---
 source/slang/slang-ir-legalize-types.cpp | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

(limited to 'source/slang')

diff --git a/source/slang/slang-ir-legalize-types.cpp b/source/slang/slang-ir-legalize-types.cpp
index dd7107b18..085c3d933 100644
--- a/source/slang/slang-ir-legalize-types.cpp
+++ b/source/slang/slang-ir-legalize-types.cpp
@@ -179,14 +179,27 @@ static LegalVal maybeMaterializeWrappedValue(IRTypeLegalizationContext* context,
 static LegalVal legalizeOperand(IRTypeLegalizationContext* context, IRInst* irValue)
 {
     LegalVal legalVal;
+
+    // Special handling for type operands
+    if (auto oldType = as<IRType>(irValue))
+    {
+        // e.g. ParameterBlock<Struct>, the inst. ParameterBlockType holds the operand `StructType`,
+        // if we don't legalize it here and the same structType is legalized somewhere else, the
+        // operand of ParameterBlockType might not get updated, and it would result in a type
+        // mismatch.
+        auto legalType = legalizeType(context, oldType);
+        if (legalType.flavor == LegalType::Flavor::simple)
+            return LegalVal::simple(legalType.getSimple());
+        // legalType is not simple, fallback to the original value
+    }
+
     if (context->mapValToLegalVal.tryGetValue(irValue, legalVal))
     {
         return maybeMaterializeWrappedValue(context, legalVal);
     }
 
     // For now, assume that anything not covered
-    // by the mapping is legal as-is.
-
+    // by the type legalization or val mapping is legal as-is.
     return LegalVal::simple(irValue);
 }
 
@@ -2386,7 +2399,8 @@ static LegalVal legalizeInst(IRTypeLegalizationContext* context, IRInst* inst)
     for (UInt aa = 0; aa < argCount; ++aa)
     {
         auto oldArg = inst->getOperand(aa);
-        auto legalArg = legalizeOperand(context, oldArg);
+
+        LegalVal legalArg = legalizeOperand(context, oldArg);
         legalArgs.add(legalArg);
 
         if (legalArg.flavor != LegalVal::Flavor::simple)
-- 
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