This was also an experiment to see if it were easier to implement a new
feature when using the instruction encoder.
Verdict: It's not that much easier, but I think it's certainly much more
readable, because the description of the Instruction annotates what each
field means. Right now, precise knowledge of x86_64 instructions is
still required because things like when to set the 64-bit flag, how to
read x86_64 instruction references, etc. are still not automatically
done for you.
In the future, this interface might make it sligtly easier to write an
assembler for x86_64, by abstracting the bit-fiddling aspects of
instruction encoding.
From my very cursory reading, it seems that the register manager doesn't
distinguish between registers that are physically the same but have
different sizes.
In that case, this means that during codegen, we can't rely on
`reg.size()` when determining the width of the operations we have to
perform. Instead, we must use some form of `ty.abiSize(self.target.*)`
to determine the size of the type we're operating with. If this size is
64 bits, then we should enable 64-bit operation.
This fixed a bug in the codegen for spilling instructions, which was
overwriting the previous stack entry with zeroes. See the modified test
case in this commit.
There are parts of it that I didn't modify because the byte
representation was important (e.g. we need to know what the exact
byte position where we store the address into the offset table is)
In std.meta.cast when casting to an enum type from an integer type, first
do a C-style cast from the source value to the tag type of the enum.
This ensures that we don't get an error due to the source value not being
representable by the enum.
In transCCast() use std.meta.cast instead of directly emitting the cast
operation since the enum's underlying type may not be known at translation
time due to an MSVC bug, see https://github.com/ziglang/zig/issues/8003Fixes#6011
Taking a detour trough a f64 is dangerous as the softfloat library
doesn't like converting sNaN values.
The error went unnoticed as an exception is raised by the library but
the stage1 compiler doesn't give a damn.
Happy LLVM 12 Release Day.
Please note that the llvm 12 tag does not include the latest commit in
the release/12.x branch, which is in fact a bug fix for a regression
that is causing a failure in Zig's test suite.
Zig master branch is tracking release/12.x, and will be enabling the
test that is fixed by that commit.
