For comparison intrinsics and for instanceof checks, make
it possible to get the the stack value produced and branch
on that directly instead of materializing a boolean to
branch on from it.
That reduces code such as
```
IF_CMPEQ L1
CONST_0
GOTO L2
L1: CONST_1
L2: IFEQ L3
```
to just one IF_CMP instruction.
KT-16194 Code with unnecessary safe call contains redundant boxing/unboxing for primitive values
KT-12839 Two null checks are generated when manually null checking platform type
Recognize some additional cases of trivial null checks and trivial instance-of checks.
A variable is "checked for null", if it is:
- a function parameter checked with 'INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull'
- checked for nullability with 'IFNULL/IFNONNULL'
- checked for nullability with 'INSTANCEOF'
(if objectref is instance-of T, then objectref is non-null)
Before analyzing nullability, introduce synthetic assumptions for execution branches
where a variable is guaranteed to be null or not null. For example, the following bytecode:
ALOAD 1 // Ljava/lang/String;
IFNULL L
<non-null branch>
L:
<null branch>
is transformed to
ALOAD 1
IFNULL L1
NEW java/lang/String
ASTORE 1 // tells analyzer that variable 1 is non-null
<non-null branch>
L:
<null branch>
L1:
ACONST_NULL
ASTORE 1 // tells analyzer that variable 1 is null
GOTO L
After the analysis is performed on a preprocessed method,
remember the results for "interesting" instructions
and revert the preprocessing transformations.
After that, perform bytecode transformations as usual.
Do not transform INSTANCEOF to-be-reified, because reification at call site
can introduce null checks. E.g.,
inline fun <reified T> isNullable() = null is T
...
assert(isNullable<String?>())
