Fix compile time regression for null ptr comparisons (#59259)

Fixes the compile time regression in
#59134 (does not address the
performance regression that should be tracked and bisected)

Author: gbaraldi

src/cgutils.cpp

@@ -1601,17 +1601,30 @@ static void undef_var_error_ifnot(jl_codectx_t &ctx, Value *ok, jl_sym_t *name,
     ctx.builder.SetInsertPoint(ifok);
 }
 
+
+static bool has_known_null_nullptr(Type *T)
+{
+    if (auto PT = cast<PointerType>(T)) {
+        auto addrspace = PT->getAddressSpace();
+        if (addrspace == AddressSpace::Generic || (AddressSpace::FirstSpecial <= addrspace && addrspace <= AddressSpace::LastSpecial)) {
+            return true;
+        }
+    }
+    return false;
+}
+
 // ctx.builder.CreateIsNotNull(v) lowers incorrectly in non-standard
 // address spaces where null is not zero
 // TODO: adapt to https://github.com/llvm/llvm-project/pull/131557 once merged
 static Value *null_pointer_cmp(jl_codectx_t &ctx, Value *v)
 {
     ++EmittedNullchecks;
     Type *T = v->getType();
-    return ctx.builder.CreateICmpNE(
-            v,
-            ctx.builder.CreateAddrSpaceCast(
-                Constant::getNullValue(ctx.builder.getPtrTy(0)), T));
+    if (has_known_null_nullptr(T))
+        return ctx.builder.CreateIsNotNull(v);
+    else
+        return ctx.builder.CreateICmpNE(v, ctx.builder.CreateAddrSpaceCast(
+            Constant::getNullValue(ctx.builder.getPtrTy(0)), T));
 }