From c1f69ca1e29811919dbd2f08a6e2dd498b80aab2 Mon Sep 17 00:00:00 2001
From: kaizhangNV <149626564+kaizhangNV@users.noreply.github.com>
Date: Wed, 2 Apr 2025 12:34:58 -0500
Subject: Metal remove void field (#6725)

* Reapply "Eliminate empty struct on metal target (#6603)" (#6711)

This reverts commit bc9dc6557fc0cc3a4c0c2ff27e636940e361cf5d.

* Remove argument in make_struct call corresponding to void field

This is a follow-up of #6543, where we leave the VoidType field as it in
make_struct call during legalization pass.

So during cleaning_void IR pass, when we remove "VoidType" from struct,
we will have to also clean up the argument corresponding to the
"VoidType" field.
---
 source/slang/slang-ir-cleanup-void.cpp | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

(limited to 'source/slang/slang-ir-cleanup-void.cpp')

diff --git a/source/slang/slang-ir-cleanup-void.cpp b/source/slang/slang-ir-cleanup-void.cpp
index 3a776fc4f..84532d0ec 100644
--- a/source/slang/slang-ir-cleanup-void.cpp
+++ b/source/slang/slang-ir-cleanup-void.cpp
@@ -122,6 +122,8 @@ struct CleanUpVoidContext
         case kIROp_StructType:
             {
                 List<IRInst*> toRemove;
+                UInt fieldCount = 0;
+                ShortList<UInt> voidFieldIndex;
                 for (auto child : inst->getChildren())
                 {
                     if (auto field = as<IRStructField>(child))
@@ -129,11 +131,33 @@ struct CleanUpVoidContext
                         if (field->getFieldType()->getOp() == kIROp_VoidType)
                         {
                             toRemove.add(field);
+                            voidFieldIndex.add(fieldCount);
                         }
                     }
+                    fieldCount++;
                 }
                 for (auto ii : toRemove)
                     ii->removeAndDeallocate();
+
+                // Once we remove the void fields in the struct, we also need update the make_struct
+                // call sites to remove the arguments corresponding to the void fields.
+                if (inst->hasUses() && voidFieldIndex.getCount())
+                {
+                    UInt currentFieldCount = fieldCount - toRemove.getCount();
+                    for (auto use = inst->firstUse; use; use = use->nextUse)
+                    {
+                        if (auto makeStructInst = as<IRMakeStruct>(use->user))
+                        {
+                            if (makeStructInst->getOperandCount() != currentFieldCount)
+                            {
+                                for (Int i = 0; i < voidFieldIndex.getCount(); i++)
+                                {
+                                    makeStructInst->removeOperand(voidFieldIndex[i]);
+                                }
+                            }
+                        }
+                    }
+                }
             }
             break;
         default:
-- 
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