[llvm] [SPIR-V] Add store legalization for ptrcast (PR #135369)

[Steven Perron via llvm-commits]

================
@@ -150,6 +150,95 @@ class SPIRVLegalizePointerCast : public FunctionPass {
     DeadInstructions.push_back(LI);
   }
 
+  // Creates an spv_insertelt instruction (equivalent to llvm's insertelement).
+  Value *makeInsertElement(IRBuilder<> &B, Value *Vector, Value *Element,
+                           unsigned Index) {
+    Type *Int32Ty = Type::getInt32Ty(B.getContext());
+    SmallVector<Type *, 4> Types = {Vector->getType(), Vector->getType(),
+                                    Element->getType(), Int32Ty};
+    SmallVector<Value *> Args = {Vector, Element, B.getInt32(Index)};
+    Instruction *NewI =
+        B.CreateIntrinsic(Intrinsic::spv_insertelt, {Types}, {Args});
+    buildAssignType(B, Vector->getType(), NewI);
+    return NewI;
+  }
+
+  // Creates an spv_extractelt instruction (equivalent to llvm's
+  // extractelement).
+  Value *makeExtractElement(IRBuilder<> &B, Type *ElementType, Value *Vector,
+                            unsigned Index) {
+    Type *Int32Ty = Type::getInt32Ty(B.getContext());
+    SmallVector<Type *, 3> Types = {ElementType, Vector->getType(), Int32Ty};
+    SmallVector<Value *> Args = {Vector, B.getInt32(Index)};
+    Instruction *NewI =
+        B.CreateIntrinsic(Intrinsic::spv_extractelt, {Types}, {Args});
+    buildAssignType(B, ElementType, NewI);
+    return NewI;
+  }
+
+  // Stores the given Src vector operand into the Dst vector, adjusting the size
+  // if required.
+  Value *storeVectorFromVector(IRBuilder<> &B, Value *Src, Value *Dst,
+                               Align Alignment) {
+    FixedVectorType *SrcType = cast<FixedVectorType>(Src->getType());
+    FixedVectorType *DstType =
+        cast<FixedVectorType>(GR->findDeducedElementType(Dst));
+    assert(DstType->getNumElements() >= SrcType->getNumElements());
+
+    LoadInst *LI = B.CreateLoad(DstType, Dst);
+    LI->setAlignment(Alignment);
+    Value *OldValues = LI;
+    buildAssignType(B, OldValues->getType(), OldValues);
+    Value *NewValues = Src;
+
+    for (unsigned I = 0; I < SrcType->getNumElements(); ++I) {
+      Value *Element =
+          makeExtractElement(B, SrcType->getElementType(), NewValues, I);
+      OldValues = makeInsertElement(B, OldValues, Element, I);
+    }
----------------
s-perron wrote:

Could we do a vector shuffle? I don't the llvm equivalant, but I believe we looked it up before.

Say the dst size is 4 and src size is 2. Then you could generate:

```
OpVectorShuffle %dest_type %src %dst 0 1 4 5
```


https://github.com/llvm/llvm-project/pull/135369