Use getPointerAddressSpace instead of cast<PointerType>.getAddressSpace.

The former also handles vectors of pointers, which can occur after vectorization:

```
#5  0x00007f5bfe94de5e in llvm::cast<llvm::PointerType, llvm::Type> (Val=<optimized out>) at llvm/Support/Casting.h:578
578	  assert(isa<To>(Val) && "cast<Ty>() argument of incompatible type!");

(rr) up
#6  GCInvariantVerifier::visitAddrSpaceCastInst (this=this@entry=0x7ffd022fbf56, I=...) at julia/src/llvm-gc-invariant-verifier.cpp:66
66	    unsigned ToAS = cast<PointerType>(I.getDestTy())->getAddressSpace();

(rr) call I.dump()
%23 = addrspacecast <4 x ptr addrspace(10)> %wide.load to <4 x ptr addrspace(11)>, !dbg !43
```

src/cgutils.cpp

@@ -57,7 +57,7 @@ static Value *maybe_decay_untracked(jl_codectx_t &ctx, Value *V)
 static Value *decay_derived(jl_codectx_t &ctx, Value *V)
 {
     Type *T = V->getType();
-    if (cast<PointerType>(T)->getAddressSpace() == AddressSpace::Derived)
+    if (T->getPointerAddressSpace() == AddressSpace::Derived)
         return V;
     // Once llvm deletes pointer element types, we won't need it here any more either.
     Type *NewT = PointerType::getWithSamePointeeType(cast<PointerType>(T), AddressSpace::Derived);
@@ -68,7 +68,7 @@ static Value *decay_derived(jl_codectx_t &ctx, Value *V)
 static Value *maybe_decay_tracked(jl_codectx_t &ctx, Value *V)
 {
     Type *T = V->getType();
-    if (cast<PointerType>(T)->getAddressSpace() != AddressSpace::Tracked)
+    if (T->getPointerAddressSpace() != AddressSpace::Tracked)
         return V;
     Type *NewT = PointerType::getWithSamePointeeType(cast<PointerType>(T), AddressSpace::Derived);
     return ctx.builder.CreateAddrSpaceCast(V, NewT);
@@ -295,7 +295,7 @@ void jl_debugcache_t::initialize(Module *m) {
 
 static Value *emit_pointer_from_objref(jl_codectx_t &ctx, Value *V)
 {
-    unsigned AS = cast<PointerType>(V->getType())->getAddressSpace();
+    unsigned AS = V->getType()->getPointerAddressSpace();
     if (AS != AddressSpace::Tracked && AS != AddressSpace::Derived)
         return V;
     V = decay_derived(ctx, V);

src/llvm-alloc-opt.cpp

@@ -1067,10 +1067,11 @@ void Optimizer::splitOnStack(CallInst *orig_inst)
                     store_ty = T_pjlvalue;
                 }
                 else {
-                    store_ty = PointerType::getWithSamePointeeType(T_pjlvalue, cast<PointerType>(store_ty)->getAddressSpace());
+                    store_ty = PointerType::getWithSamePointeeType(
+                        T_pjlvalue, store_ty->getPointerAddressSpace());
                     store_val = builder.CreateBitCast(store_val, store_ty);
                 }
-                if (cast<PointerType>(store_ty)->getAddressSpace() != AddressSpace::Tracked)
+                if (store_ty->getPointerAddressSpace() != AddressSpace::Tracked)
                     store_val = builder.CreateAddrSpaceCast(store_val, pass.T_prjlvalue);
                 newstore = builder.CreateStore(store_val, slot.slot);
             }

src/llvm-gc-invariant-verifier.cpp

@@ -62,8 +62,8 @@ struct GCInvariantVerifier : public InstVisitor<GCInvariantVerifier> {
 };
 
 void GCInvariantVerifier::visitAddrSpaceCastInst(AddrSpaceCastInst &I) {
-    unsigned FromAS = cast<PointerType>(I.getSrcTy())->getAddressSpace();
-    unsigned ToAS = cast<PointerType>(I.getDestTy())->getAddressSpace();
+    unsigned FromAS = I.getSrcTy()->getPointerAddressSpace();
+    unsigned ToAS = I.getDestTy()->getPointerAddressSpace();
     if (FromAS == 0)
         return;
     Check(ToAS != AddressSpace::Loaded && FromAS != AddressSpace::Loaded,
@@ -81,7 +81,7 @@ void GCInvariantVerifier::checkStoreInst(Type *VTy, unsigned AS, Value &SI) {
     if (VTy->isPointerTy()) {
         /* We currently don't obey this for arguments. That's ok - they're
            externally rooted. */
-        unsigned AS = cast<PointerType>(VTy)->getAddressSpace();
+        unsigned AS = VTy->getPointerAddressSpace();
         Check(AS != AddressSpace::CalleeRooted &&
               AS != AddressSpace::Derived,
               "Illegal store of decayed value", &SI);
@@ -108,14 +108,14 @@ void GCInvariantVerifier::visitAtomicCmpXchgInst(AtomicCmpXchgInst &SI) {
 void GCInvariantVerifier::visitLoadInst(LoadInst &LI) {
     Type *Ty = LI.getType();
     if (Ty->isPointerTy()) {
-        unsigned AS = cast<PointerType>(Ty)->getAddressSpace();
+        unsigned AS = Ty->getPointerAddressSpace();
         Check(AS != AddressSpace::CalleeRooted &&
               AS != AddressSpace::Derived,
               "Illegal load of gc relevant value", &LI);
     }
     Ty = LI.getPointerOperand()->getType();
     if (Ty->isPointerTy()) {
-        unsigned AS = cast<PointerType>(Ty)->getAddressSpace();
+        unsigned AS = Ty->getPointerAddressSpace();
         Check(AS != AddressSpace::CalleeRooted,
               "Illegal load of callee rooted value", &LI);
     }
@@ -131,7 +131,7 @@ void GCInvariantVerifier::visitReturnInst(ReturnInst &RI) {
     Type *RTy = RI.getReturnValue()->getType();
     if (!RTy->isPointerTy())
         return;
-    unsigned AS = cast<PointerType>(RTy)->getAddressSpace();
+    unsigned AS = RTy->getPointerAddressSpace();
     Check(!isSpecialAS(AS) || AS == AddressSpace::Tracked,
           "Only gc tracked values may be directly returned", &RI);
 }
@@ -140,7 +140,7 @@ void GCInvariantVerifier::visitGetElementPtrInst(GetElementPtrInst &GEP) {
     Type *Ty = GEP.getType();
     if (!Ty->isPointerTy())
         return;
-    unsigned AS = cast<PointerType>(Ty)->getAddressSpace();
+    unsigned AS = Ty->getPointerAddressSpace();
     if (!isSpecialAS(AS))
         return;
     /* We're actually ok with GEPs here, as long as they don't feed into any
@@ -170,8 +170,9 @@ void GCInvariantVerifier::visitCallInst(CallInst &CI) {
                 continue;
             }
             Type *Ty = Arg->getType();
-            Check(Ty->isPointerTy() && cast<PointerType>(Ty)->getAddressSpace() == AddressSpace::Tracked,
-                "Invalid derived pointer in jlcall", &CI);
+            Check(Ty->isPointerTy() &&
+                      Ty->getPointerAddressSpace() == AddressSpace::Tracked,
+                  "Invalid derived pointer in jlcall", &CI);
         }
     }
 }

src/llvm-propagate-addrspaces.cpp

@@ -60,7 +60,7 @@ struct PropagateJuliaAddrspacesVisitor : public InstVisitor<PropagateJuliaAddrsp
 };
 
 static unsigned getValueAddrSpace(Value *V) {
-    return cast<PointerType>(V->getType())->getAddressSpace();
+    return V->getType()->getPointerAddressSpace();
 }
 
 static bool isSpecialAS(unsigned AS) {