Although a let-field can never be mutated, a release or consume of the class must be considered as writing to such a field.
This change removes the special handling of let-fields in two places, where they don't belong.
Class fields are handled by ImmutableScope anyway.
Handling of global let-variable is temporarily removed by this commit.
Fixes a miscompile.
rdar://142996449
Add `Value.constantAccessPath`. It is like `accessPath`, but ensures that the projectionPath only contains "constant" elements.
This means: if the access contains an `index_addr` projection with a non-constant index, the `projectionPath` does _not_ contain the `index_addr`.
Instead, the `base` is an `AccessBase.index` which refers to the `index_addr`.
The main changes are:
*) Rewrite everything in swift. So far, parts of memory-behavior analysis were already implemented in swift. Now everything is done in swift and lives in `AliasAnalysis.swift`. This is a big code simplification.
*) Support many more instructions in the memory-behavior analysis - especially OSSA instructions, like `begin_borrow`, `end_borrow`, `store_borrow`, `load_borrow`. The computation of end_borrow effects is now much more precise. Also, partial_apply is now handled more precisely.
*) Simplify and reduce type-based alias analysis (TBAA). The complexity of the old TBAA comes from old days where the language and SIL didn't have strict aliasing and exclusivity rules (e.g. for inout arguments). Now TBAA is only needed for code using unsafe pointers. The new TBAA handles this - and not more. Note that TBAA for classes is already done in `AccessBase.isDistinct`.
*) Handle aliasing in `begin_access [modify]` scopes. We already supported truly immutable scopes like `begin_access [read]` or `ref_element_addr [immutable]`. For `begin_access [modify]` we know that there are no other reads or writes to the access-address within the scope.
*) Don't cache memory-behavior results. It turned out that the hit-miss rate was pretty bad (~ 1:7). The overhead of the cache lookup took as long as recomputing the memory behavior.
All SILArgument types are "block arguments". There are three kinds:
1. Function arguments
2. Phis
3. Terminator results
In every situation where the source of the block argument matters, we
need to distinguish between these three. Accidentally failing to
handle one of the cases is an perpetual source of compiler
bugs. Attempting to handle both phis and terminator results uniformly
is *always* a bug, especially once OSSA has phi flags. Even when all
cases are handled correctly, the code that deals with data flow across
blocks is incomprehensible without giving each case a type. This
continues to be a massive waste of time literally every time I review
code that involves cross-block control flow.
Unfortunately, we don't have these C++ types yet (nothing big is
blocking that, it just wasn't done). That's manageable because we can
use wrapper types on the Swift side for now. Wrapper types don't
create any more complexity than protocols, but they do sacrifice some
usability in switch cases.
There is no reason for a BlockArgument type. First, a function
argument is a block argument just as much as any other. BlockArgument
provides no useful information beyond Argument. And it is nearly
always a mistake to care about whether a value is a function argument
and not care whether it is a phi or terminator result.
* split the `PassContext` into multiple protocols and structs: `Context`, `MutatingContext`, `FunctionPassContext` and `SimplifyContext`
* change how instruction passes work: implement the `simplify` function in conformance to `SILCombineSimplifyable`
* add a mechanism to add a callback for inserted instructions
Replace the generic `List` with the (non-generic) `InstructionList` and `BasicBlockList`.
The `InstructionList` is now a bit different than the `BasicBlockList` because it supports that instructions are deleted while iterating over the list.
Also add a test pass which tests instruction modification while iteration.
And simplify it.
This struct is not really needed by clients. It's just needed internally in 'Value.accessPath` (and similar properties) to compute the access path.
Dead-end blocks are blocks from which there is no path to the function exit (`return`, `throw` or unwind).
These are blocks which end with an unreachable instruction and blocks from which all paths end in "unreachable" blocks.
Replace the `struct EscapeInfo` with a simpler API, just consisting of methods of `ProjectedValue` and `Value`:
* `isEscaping()`
* `isAddressEscaping()`
* `visit()`
* `visitAddress()`
A projected value consists of the original value and a projection path.
For example, if the `value` is of type `struct S { var x: Int }` and `path` is `s0`, then the projected value represents field `x` of the original value.
Also, use ProjectedValue instead of AccessStoragePath.
It doesn't make sense to let getAccessPathWithScope return an `EnclosingScope` as the second tuple element, because in case it's a `base`, it duplicates the `AccessBase` (which is returned in the first tuple element).
Instead just return an optional `BeginAccessInst` which is not nil if such an "scope" is found.
Now that `AccessBase` is an enum, it makes sense to add an `unidentified` case. This avoids dealing with optional AccessBases in several place.
Clients don't need to make both, an optional check and a switch, but can check for unidentified access bases just in a single switch statement.
Provides a list of instructions, which reference a function.
A function "use" is an instruction in another (or the same) function which references the function.
In most cases those are `function_ref` instructions, but can also be e.g. `keypath` instructions.
'FunctionUses' performs an analysis of all functions in the module and collects instructions which reference other functions.
This utility can be used to do inter-procedural caller-analysis.
