Merge pull request #58 from ngzhian/remove-fpenv

Remove fpenv from overview, add proposed spec text on Relaxed operations

Author: ngzhian

proposals/relaxed-simd/Overview.md

@@ -59,54 +59,14 @@ that instruction). One can imagine splitting an application's module and
 running them on multiple runtimes, where the runtimes produce
 different results - this can be surprising to the application.
 
-Applications can specify their consistency needs using a new module-level
-entity `fpenv` (name subject to change). A `fpenv` is defined in the `fpenv`
-section of a module.  All Relaxed SIMD instructions will take an additional
-`varuint32` immediate, which is an index into the `fpenv` index space:
-
-```wast
-(module
-  (func (param v128 v128 v128)
-    (f32x4.qfma $fpu (local.get 0) (local.get 1) (local.get 2)) ;; (1)
-    ;; ...
-    (f32x4.qfma $fpu (local.get 0) (local.get 1) (local.get 2)) ;; (2)
-  )
-  (fpenv $fpu 0))
-```
-
-In the example above, both `f32x4.qfma` instructions refer to the same `fpenv`,
-and will get the same results when given the same input.
-
-A `fpenv` has a single `varuint32` attribute which is reserved for future
-extensibility and must be `0` for now.  The value of an `fpenv` is
-non-deterministically computed when the module which declares it is
-instantiated.  This value determines the semantics of the instructions that
-uses it as an immediate.
-
-As such, all the non-determinism of Relaxed SIMD is encapsulated in `fpenv`,
-which makes Relaxed SIMD instructions themselves deterministic.
-
-Modules can import/export an `fpenv` to specify consistency requirements:
-
-```wast
-;; module a
-(module
-  (fpenv $fpu (export "foo") 0)
-  (func (param v128 v128 v128)
-    (f32x4.qfma $fpu (local.get 0) (local.get 1) (local.get 2)))) ;; (1)
-```
-
-```wast
-;; module b
-(module
-  (import "a" "foo" (fpenv $fpu 0))
-  (func (param v128 v128 v128)
-    (f32x4.qfma $fpu (local.get 0) (local.get 1) (local.get 2)))) ;; (2)
-```
-
-In the above example, the same `fpenv` is exported by module `a`, and imported
-by module `b`, so instructions `(1)` and `(2)` will consistently return the
-same results when given the same inputs.
+The specification is updated with the idea of "Relaxed operations":
+
+> Some operators are host-dependent, because the set of possible results may
+> depend on properties of the host environment (such as hardware). Technically,
+> each such operator produces a fixed-size list of sets of allowed values. For
+> each execution of the operator in the same environment, only values from the
+> set at the same position in the list are returned, i.e., each environment
+> globally chooses a fixed projection for each operator.
 
 ## Instructions