Compiler: fix inferred nothrow effects for add_ptr and sub_ptr (#59720)

Previously, add_ptr and sub_ptr intrinsics were incorrectly inferred as
potentially throwing because they fell through to the general primitive
type check, which was incorrect after #53687 changed them. This adds
explicit handling in intrinsic_exct to return Union{} (nothrow) when
given correct argument types (Ptr and UInt), similar to #57398.

Fixes #57557

Written by Claude

Author: vtjnash

Compiler/src/tfuncs.jl

@@ -2978,6 +2978,13 @@ function intrinsic_exct(𝕃::AbstractLattice, f::IntrinsicFunction, argtypes::V
         return Union{}
     end
 
+    if f === Intrinsics.add_ptr || f === Intrinsics.sub_ptr
+        if !(argtypes[1] ⊑ Ptr && argtypes[2] ⊑ UInt)
+            return TypeError
+        end
+        return Union{}
+    end
+
     # The remaining intrinsics are math/bits/comparison intrinsics.
     # All the non-floating point intrinsics work on primitive values of the same type.
     isshift = f === shl_int || f === lshr_int || f === ashr_int

Compiler/test/effects.jl

@@ -1438,6 +1438,11 @@ let effects = Base.infer_effects(Core.Intrinsics.pointerset, Tuple{Vararg{Any}})
     @test Compiler.is_consistent(effects)
     @test !Compiler.is_effect_free(effects)
 end
+@test Compiler.intrinsic_nothrow(Core.Intrinsics.add_ptr, Any[Ptr{Int}, UInt])
+@test Compiler.intrinsic_nothrow(Core.Intrinsics.sub_ptr, Any[Ptr{Int}, UInt])
+@test !Compiler.intrinsic_nothrow(Core.Intrinsics.add_ptr, Any[UInt, UInt])
+@test !Compiler.intrinsic_nothrow(Core.Intrinsics.sub_ptr, Any[UInt, UInt])
+@test Compiler.is_nothrow(Base.infer_effects(+, Tuple{Ptr{UInt8}, UInt}))
 # effects modeling for atomic intrinsics
 # these functions especially need to be marked !effect_free since they imply synchronization
 for atomicfunc = Any[