[llvm] [SPIR-V] Emit SPIR-V bitcasts between source/expected pointer type (PR #69621)

[Ilia Diachkov via llvm-commits]

================
@@ -265,6 +281,85 @@ Instruction *SPIRVEmitIntrinsics::visitBitCastInst(BitCastInst &I) {
   return NewI;
 }
 
+void SPIRVEmitIntrinsics::insertPtrCastInstr(Instruction *I) {
+  Value *Pointer;
+  Type *ExpectedElementType;
+  unsigned OperandToReplace;
+  if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+    Pointer = SI->getPointerOperand();
+    ExpectedElementType = SI->getValueOperand()->getType();
+    OperandToReplace = 1;
+  } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+    Pointer = LI->getPointerOperand();
+    ExpectedElementType = LI->getType();
+    OperandToReplace = 0;
+  } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
+    Pointer = GEPI->getPointerOperand();
+    ExpectedElementType = GEPI->getSourceElementType();
+    OperandToReplace = 0;
+  } else {
+    return;
+  }
+
+  // If Pointer is the result of nop BitCastInst (ptr -> ptr), use the source
+  // pointer instead. The BitCastInst should be later removed when visited.
+  if (BitCastInst *BC = dyn_cast<BitCastInst>(Pointer))
+    Pointer = BC->getOperand(0);
+
+  // Do not emit spv_ptrcast if Pointer is a GlobalValue of expected type.
+  GlobalValue *GV = dyn_cast<GlobalValue>(Pointer);
+  if (GV && GV->getValueType() == ExpectedElementType)
+    return;
+
+  setInsertPointSkippingPhis(*IRB, I);
+  Constant *ExpectedElementTypeConst =
+      Constant::getNullValue(ExpectedElementType);
+  ConstantAsMetadata *CM =
+      ValueAsMetadata::getConstant(ExpectedElementTypeConst);
+  MDTuple *TyMD = MDNode::get(F->getContext(), CM);
+  MetadataAsValue *VMD = MetadataAsValue::get(F->getContext(), TyMD);
+  unsigned AddressSpace = Pointer->getType()->getPointerAddressSpace();
+  bool FirstPtrCastOrAssignPtrType = true;
+
+  // Do not emit new spv_ptrcast if equivalent one already exists or when
+  // spv_assign_ptr_type already targets this pointer with the same element
+  // type.
+  for (auto User : Pointer->users()) {
+    if (auto *II = dyn_cast<IntrinsicInst>(User)) {
+      if ((II->getIntrinsicID() != Intrinsic::spv_assign_ptr_type &&
+           II->getIntrinsicID() != Intrinsic::spv_ptrcast) ||
+          II->getOperand(0) != Pointer)
+        continue;
+
+      FirstPtrCastOrAssignPtrType = false;
+      if (II->getOperand(1) == VMD &&
+          dyn_cast<ConstantInt>(II->getOperand(2))->getSExtValue() ==
+              AddressSpace)
+        return;
+    }
----------------
iliya-diyachkov wrote:

Maybe we can reduce the indentation:
```
auto *II = dyn_cast<IntrinsicInst>(User)
if (!II)
  continue;
```

https://github.com/llvm/llvm-project/pull/69621