Closure literals are sometimes type-checked as one type then immediately converted to another
type in the AST. One particular case of this is when a closure body never throws, but the closure
is used as an argument to a function that takes a parameter that `throws`. Emitting this naively,
by emitting the closure as its original type, then converting to throws, can be expensive for
async closures, since that takes a reabstraction thunk. Even for non-async functions, we still want
to get the benefit of reabstraction optimization for the closure literal through the conversion too.
So if the function conversion just add `throws`, emit the closure as throwing, and pass down the
context abstraction pattern when emitting the closure as well.
* [SILGenFunction] Don't create redundant nested debug scopes
Instead of emitting:
```
sil_scope 4 { loc "main.swift":6:19 parent 3 }
sil_scope 5 { loc "main.swift":7:3 parent 4 }
sil_scope 6 { loc "main.swift":7:3 parent 5 }
sil_scope 7 { loc "main.swift":7:3 parent 5 }
sil_scope 8 { loc "main.swift":9:5 parent 4 }
```
Emit:
```
sil_scope 4 { loc "main.swift":6:19 parent 3 }
sil_scope 5 { loc "main.swift":7:3 parent 4 }
sil_scope 6 { loc "main.swift":9:5 parent 5 }
```
* [IRGenSIL] Diagnose conflicting shadow copies
If we attempt to store a value with the wrong type into a slot reserved
for a shadow copy, diagnose what went wrong.
* [SILGenPattern] Defer debug description of case variables
Create unique nested debug scopes for a switch, each of its case labels,
and each of its case bodies. This looks like:
```
switch ... { // Enter scope 1.
case ... : // Enter scope 2, nested within scope 1.
<body-1> // Enter scope 3, nested within scope 2.
case ... : // Enter scope 4, nested within scope 1.
<body-2> // Enter scope 5, nested within scope 4.
}
```
Use the new scope structure to defer emitting debug descriptions of case
bindings. Specifically, defer the work until we can nest the scope for a
case body under the scope for a pattern match.
This fixes SR-7973, a problem where it was impossible to inspect a case
binding in lldb when stopped at a case with multiple items.
Previously, we would emit the debug descriptions too early (in the
pattern match), leading to duplicate/conflicting descriptions. The only
reason that the ambiguous description was allowed to compile was because
the debug scopes were nested incorrectly.
rdar://41048339
* Update tests
LLVM r356789 changed the format of textual IR to print nameless
blocks with labels instead of comments with "; <label>". Adjust Swift
tests to match. I also updated the utils/viewcfg script to match.
Switch statements generate at least one anonymous match variable per
case, which consumes both a lot of stack space and an explosion of
range extension depencies due to the way case statements are scoped.
rdar://problem/34326355
Instead of appending a character for each substitution, we now prefix the substitution with the repeat count, e.g.
AbbbbB -> A5B
The same is done for known-type substitutions, e.g.
SiSiSi -> S3i
This significantly shrinks mangled names which contain large lists of the same type, like
func foo(_ x: (Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int))
rdar://problem/30707433
Even at -Onone one SILValue can back up more than one local source variable.
This commit changes the list of variable values into a set.
<rdar://problem/28467349>
