For logical instructions such as AND, there is a constraint that the N part of the bitmask immediate must be 0. We weren't respecting this condition previously and were silently emitting undefined instructions. Check for this condition in the assembler and tweak the backend to correctly detect whether a number could be encoded as an immediate in a 32 bit logical instruction. Due to the nature of the immediate encoding, the same numeric value encodes differently depending on the size of the register the instruction works on. We currently don't have cases where we use 32 bit immediates but we ran into this encoding issue during development.
* Introduce InstructionOffset for AArch64 There are a lot of instructions on AArch64 where we take an offset from PC in terms of the number of instructions. This is for loading a value relative to the PC or for jumping. We were usually accepting an A64Opnd or an i32. It can get confusing and inconsistent though because sometimes you would divide by 4 to get the number of instructions or multiply by 4 to get the number of bytes. This commit adds a struct that wraps an i32 in order to keep all of that logic in one place. It makes it much easier to read and reason about how these offsets are getting used. * Use b instruction when the offset fits on AArch64
* Better b.cond usage on AArch64 When we're lowering a conditional jump, we previously had a bit of a complicated setup where we could emit a conditional jump to skip over a jump that was the next instruction, and then write out the destination and use a branch register. Now instead we use the b.cond instruction if our offset fits (not common, but not unused either) and if it doesn't we write out an inverse condition to jump past loading the destination and branching directly. * Added an inverse fn for Condition (#443) Prevents the need to pass two params and potentially reduces errors. Co-authored-by: Jimmy Miller <jimmyhmiller@jimmys-mbp.lan> Co-authored-by: Maxime Chevalier-Boisvert <maximechevalierb@gmail.com> Co-authored-by: Jimmy Miller <jimmyhmiller@jimmys-mbp.lan>
There are a lot of times when encoding AArch64 instructions that we need to represent an integer value with a custom fixed width. For example, the offset for a B instruction is 26 bits, so we store an i32 on the instruction struct and then mask it when we encode. We've been doing this masking everywhere, which has worked, but it's getting a bit copy-pasty all over the place. This commit centralizes that logic to make sure we stay consistent.