as explainded at https://llvm.org/docs/LangRef.html#vector-type :
"In general vector elements are laid out in memory in the same way as array types.
Such an analogy works fine as long as the vector elements are byte sized.
However, when the elements of the vector aren’t byte sized it gets a bit more complicated.
One way to describe the layout is by describing what happens when a vector such
as <N x iM> is bitcasted to an integer type with N*M bits, and then following the
rules for storing such an integer to memory."
"When <N*M> isn’t evenly divisible by the byte size the exact memory layout
is unspecified (just like it is for an integral type of the same size)."
The special case to take advantage of llvm's intrinsic
was generating invalid llvm ir:
```
Invalid bitcast
%60 = bitcast <2 x i2> %59 to i8, !dbg !3122
thread 145453 panic: LLVM module verification failed
```
Most of this migration was performed automatically with `zig fmt`. There
were a few exceptions which I had to manually fix:
* `@alignCast` and `@addrSpaceCast` cannot be automatically rewritten
* `@truncate`'s fixup is incorrect for vectors
* Test cases are not formatted, and their error locations change
Previously this worked for array to vector where the element type
matched exactly (e.g `[4]u8` to `@Vector(4, u8)`) since that is
performed with a simple `.bitcast` operation, but now it also works for
types where the array is coercible to the vector type (e.g `[4]u8` to
`@Vector(4, u16)`).
This is consistent with how coercion for vectors work. So now you can do
this:
```
var a: @Vector(2, u16) = .{1, 2};
var b: @Vector(2, u8) = .{2, 1};
const c = @min(a, b);
```
where previously you had to cast explicitly:
```
var a: @Vector(2, u16) = .{1, 2};
var b: @Vector(2, u8) = .{2, 1};
var c: @Vector(2, u16) = b;
const c = @min(a, c);
```
Many `Type`s can correspond to the same `CType`, so this reduces the
number of used locals by 27760 when compiling only-c.
Also, disabled some tests that were only passing by accident and
shouldn't really be considered working.
This reverts commit 3370d58956.
This commit was done with an LLVM build that did not have assertions
enabled. There are LLVM assertions being triggered due to this commit.
Reopens#10627Reopens#12013Reopens#12027
