Type annotations for instruction operands are omitted, e.g.
```
%3 = struct $S(%1, %2)
```
Operand types are redundant anyway and were only used for sanity checking in the SIL parser.
But: operand types _are_ printed if the definition of the operand value was not printed yet.
This happens:
* if the block with the definition appears after the block where the operand's instruction is located
* if a block or instruction is printed in isolation, e.g. in a debugger
The old behavior can be restored with `-Xllvm -sil-print-types`.
This option is added to many existing test files which check for operand types in their check-lines.
The new implementation has several benefits compared to the old C++ implementation:
* It is significantly simpler. It optimizes each load separately instead of all at once with bit-field based dataflow.
* It's using alias analysis more accurately which enables more loads to be optimized
* It avoids inserting additional copies in OSSA
The algorithm is a data flow analysis which starts at the original load and searches for preceding stores or loads by following the control flow in backward direction.
The preceding stores and loads provide the "available values" with which the original load can be replaced.
When merging many blocks to a single block (in the wrong order), instructions are getting moved over and over again.
This is quadratic and can result in very long compile times for large functions.
To fix this, always move the instruction to smaller block to the larger block.
rdar://problem/56268570
Global initializers are executed only once.
Therefore it's possible to hoist such an initializer call to a loop pre-header - in case there are no conflicting side-effects in the loop before the call.
Also, the call must post-dominate the loop pre-header. Otherwise it would be executed speculatively.
