Strings from symbolVal not simplified at compile time

Compiling

{-# LANGUAGE DataKinds #-}

module Test where

import GHC.TypeLits
import Data.Proxy

testAA :: Bool
testAA = symbolVal (Proxy :: Proxy "A") == symbolVal (Proxy :: Proxy "A")

testAB :: Bool
testAB = symbolVal (Proxy :: Proxy "A") == symbolVal (Proxy :: Proxy "B")

with

ghc -O -ddump-simpl -dsuppress-all Test.hs

yields:

-- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
testAA2
testAA2 = "A"#

-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
testAA1
testAA1 = unpackCString# testAA2

-- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
testAB1
testAB1 = "B"#

-- RHS size: {terms: 4, types: 0, coercions: 0, joins: 0/0}
testAB
testAB = eqString testAA1 (unpackCString# testAB1)

-- RHS size: {terms: 3, types: 0, coercions: 0, joins: 0/0}
testAA
testAA = eqString testAA1 testAA1

Removing testAA makes testAB simplify to False, and so does removing testAB's type signature.

I would expect each definition to simplify to True or False, no matter whether it has a type signature or whether the same string is used elsewhere in the same file.

Trac metadata

Trac field	Value
Version	8.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (CodeGen)
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