[clang] Revise the modules document for clarity (PR #90237)

[via cfe-commits]

================
@@ -530,43 +527,43 @@ Now the linkage name of ``NS::foo()`` will be ``_ZN2NS3fooEv``.
 Module Initializers
 ~~~~~~~~~~~~~~~~~~~
 
-All the importable module units are required to emit an initializer function.
-The initializer function should contain calls to importing modules first and
-all the dynamic-initializers in the current module unit then.
-
-Translation units explicitly or implicitly importing named modules must call
-the initializer functions of the imported named modules within the sequence of
-the dynamic-initializers in the TU. Initializations of entities at namespace
-scope are appearance-ordered. This (recursively) extends into imported modules
-at the point of appearance of the import declaration.
+All importable module units are required to emit an initializer function. The
+initializer function emits calls to imported modules first followed by calls
+to all to dynamic initializers in the current module unit.
 
-It is allowed to omit calls to importing modules if it is known empty.
+Translation units that explicitly or implicitly import a named module must call
+the initializer functions of the imported named module within the sequence of
+the dynamic initializers in the translation unit. Initializations of entities
+at namespace scope are appearance-ordered. This (recursively) extends to
+imported modules at the point of appearance of the import declaration.
 
-It is allowed to omit calls to importing modules for which is known to be called.
+If the imported module is known to be empty, the call to its initializer may be
+omitted. Additionally, if the imported module is known to have already been
+imported, the call to its initializer may be omitted.
 
 Reduced BMI
 -----------
 
-To support the 2 phase compilation model, Clang chose to put everything needed to
-produce an object into the BMI. But every consumer of the BMI, except itself, doesn't
-need such informations. It makes the BMI to larger and so may introduce unnecessary
-dependencies into the BMI. To mitigate the problem, we decided to reduce the information
-contained in the BMI.
+To support the two-phase compilation model, Clang puts everything needed to
+produce an object into the BMI. However, other consumers of the BMI generally
+don't need that informations. This makes the BMI larger and may introduce
+unnecessary dependencies for the BMI. To mitigate the problem, Clang added a
+compiler option to reduce the information contained in the BMI. These two
+formats are known as Full BMI and Reduced BMI, respectively.
 
-To be clear, we call the default BMI as Full BMI and the new introduced BMI as Reduced
-BMI.
+Users can use the ``-fexperimental-modules-reduced-bmi`` option to produce a
+Reduced BMI.
----------------
cor3ntin wrote:

We should find a better name in a subsequent pr

https://github.com/llvm/llvm-project/pull/90237