Fix copying initialized members in EmitInsertValueToStruct

Description:
The function getAllDefinedMembers has a bug - it will not return any indices if the insertvalue instruction uses a constant struct instead of undef as a starting point.
For example:
  %29 = insertvalue %__StructSOALayout_ <{ i32 194816, i32 undef, i32 undef, <1 x float> undef }>, i32 %18, 1		; visa id: 45
  %30 = insertvalue %__StructSOALayout_ %29, i32 0, 2		; visa id: 47
In this case, when emitting instructions for %30, we should see that the indices 0 and 1 are initialized (with i32 194816 and i32 %18).
However, we don't and we end up losing those values.

The fix makes getAllDefinedMembers return all initialized indices by recursively traversing the constant struct (recursively in case the struct has structs inside it)

Author: jaladreips

IGC/Compiler/CISACodeGen/EmitVISAPass.cpp

@@ -2961,7 +2961,7 @@ void EmitPass::EmitInsertValueToStruct(InsertValueInst* inst)
             //  %13 = insertvalue %9, i32 %scalar40, 2
             //  %14 = insertvalue %13, i32 %scalar41, 3
             //
-            std::list<ArrayRef<unsigned>> toBeCopied;
+            SmallVector<std::vector<unsigned>> toBeCopied;
             getAllDefinedMembers(src0, toBeCopied);
             for (const auto& II : toBeCopied)
             {
@@ -3128,7 +3128,7 @@ void EmitPass::EmitInsertValueToLayoutStruct(InsertValueInst* IVI)
             // Most often, SrcV has just one defined value and calling
             // emitCopyToOrFromLayoutStruct() would copy all, thus special
             // handling here to avoid copy undefined values.
-            std::list<ArrayRef<unsigned>> toBeCopied;
+            SmallVector<std::vector<unsigned>> toBeCopied;
             getAllDefinedMembers(src0, toBeCopied);
             for (const auto& II : toBeCopied)
             {

IGC/Compiler/CISACodeGen/MemOpt.cpp

@@ -5234,23 +5234,50 @@ void getStructMemberOffsetAndType_2(const DataLayout* DL,
     return;
 }
 
+static void searchForDefinedMembers(const ConstantAggregate* S, const std::vector<unsigned>& currentIndices, SmallVectorImpl<std::vector<unsigned>>& fieldsTBC)
+{
+    for (unsigned i = 0; i < S->getNumOperands(); i++)
+    {
+        auto indices = currentIndices;
+        indices.push_back(i);
+        auto* E = S->getAggregateElement(i);
+        if (isa<UndefValue>(E))
+            continue;
+
+        if (auto* SE = dyn_cast<ConstantAggregate>(E))
+        {
+            searchForDefinedMembers(SE, indices, fieldsTBC);
+        }
+        else
+        {
+            fieldsTBC.push_back(indices);
+        }
+
+    }
+}
+
 void getAllDefinedMembers (const Value* IVI,
-    std::list<ArrayRef<unsigned>>& fieldsTBC)
+    SmallVectorImpl<std::vector<unsigned>>& fieldsTBC)
 {
     IGC_ASSERT(IVI != nullptr);
     const Value* V = IVI;
     while (isa<InsertValueInst>(V))
     {
         const InsertValueInst* I = cast<const InsertValueInst>(V);
-        fieldsTBC.push_front(I->getIndices());
+        fieldsTBC.push_back(I->getIndices().vec());
         V = I->getOperand(0);
     }
-    if (!isa<UndefValue>(V))
+
+    // at the end we may have a constant struct like this:
+    // % 28 = insertvalue % __StructSOALayout_ < { i32 194816, i32 undef, i32 undef, <1 x float> undef } > , i32 % 17, 1
+    // we should traverse it and find the indices pointing to the constant values
+    if (auto* S = dyn_cast<ConstantAggregate>(V))
     {
-        // Don't know for sure, assume all have been defined.
-        fieldsTBC.clear();
-        StructType* stTy = cast<StructType>(IVI->getType());
-        fieldsTBC.insert(fieldsTBC.end(), 0, stTy->getNumElements() - 1);
+        std::vector<unsigned> indices = {};
+        searchForDefinedMembers(S, indices, fieldsTBC);
     }
+
+    // reverse the vector to get the ascending order of indices
+    std::reverse(fieldsTBC.begin(), fieldsTBC.end());
 }
 }

IGC/Compiler/CISACodeGen/MemOpt.h

@@ -91,7 +91,7 @@ namespace IGC {
     //
     //  The value %9 will return {0, 1}, and %10 will return {0, 1, 2}.
     void getAllDefinedMembers(const Value* IVI,
-        std::list<ArrayRef<unsigned>>& fieldsTBC);
+        SmallVectorImpl<std::vector<unsigned>>& fieldsTBC);
 }
 
 #endif // _CISA_MEMOPT_H_