xenia/TODO.md

## Loader

Set all function variable addresses to the thunks. Since we handle the thunks
specially the variables are just used as function pointer storage.

## Kernel

Ordered:
```
RtlInitializeCriticalSection/RtlInitializeCriticalSectionAndSpinCount
RtlEnterCriticalSection/RtlLeaveCriticalSection
NtCreateEvent
NtClose
NtWaitForSingleObjectEx
RtlFreeAnsiString/RtlFreeUnicodeString
RtlUnicodeStringToAnsiString
```

Others:
```
NtCreateEvent
NtWaitForSingleObjectEx

RtlCompareMemoryUlong
RtlNtStatusToDosError
RtlRaiseException

NtCreateFile/NtOpenFile
NtClose
NtReadFile/NtReadFileScatter
NtQueryFullAttributesFile
NtQueryInformationFile/NtSetInformationFile
NtQueryDirectoryFile/NtQueryVolumeInformationFile

NtDuplicateObject

KeBugCheck:
// VOID
// _In_  ULONG BugCheckCode
```

## Instructions

```
rlwimix
rldiclx
addcx
addex
addicx
andisx
cntlzdx
dcbf
dcbz
divdux
divdx
divwx
eieio
eqvx
extshx
extswx
fabsx
faddsx
faddx
fcfidx
fcmpu
fctidzx
fctiwzx
fdivsx
fdivx
fmaddsx
fmaddx
fmrx
fmsubsx
fmsubx
fmulsx
fmulx
fnegx
fnmsubsx
fnmsubx
frspx
fselx
fsqrtx
fsubsx
fsubx
ldarx
ldx
lfd
lfdx
lfs
lfsu
lfsux
lfsx
lha
lhax
lhzu
lhzx
lwa
lwarx
lwax
lwbrx
lwzux
mftb
mulldx
nandx
negx
orcx
rldiclx
rldicrx
rldimix
rlwnmx
sldx
sradix
sradx
srawx
srdx
srwx
stbx
stdcx
stdx
stfd
stfdu
stfdx
stfiwx
stfs
stfsu
stfsx
stwbrx
stwcx
stwux
subfcx
subfzex
sync
```

### XER CA bit (carry)

Not sure the way I'm doing this is right. addic/subficx/etc set it to the value
of the overflow bit from the LLVM *_with_overflow intrinsic.

### Overflow

Overflow bits can be set via the intrinsics:
`llvm.sadd.with.overflow`/etc
It'd be nice to avoid doing this unless absolutely required. The SDB could
walk functions to see if they ever read or branch on the SO bit of things.

### Conditions

Condition bits are, after each function:
```
if (target_reg < 0) { CR0 = b100 | XER[SO] }
if (target_reg > 0) { CR0 = b010 | XER[SO] }
else                { CR0 = b001 | XER[SO] }
```
Most PPC instructions are optimized by the compiler to have Rc=0 and not set the
bits if possible. There are some instructions, though, that always set them.
For those, it would be nice to remove redundant sets. Maybe LLVM will do it
automatically due to the local cr? May need to split that up into a few locals
(one for each bit?) to ensure deduping.

### Branch Hinting

`@llvm.expect.i32`/`.i64` could be used with the BH bits in branches to
indicate expected values.

### Data Caching

dcbt and dcbtst could use LLVM intrinsic @llvm.prefetch.

## Codegen

### Calling convention

Experiment with fastcc? May need typedef fn ptrs to call into the JITted code.

### Function calling convention analysis

Track functions to see if they follow the standard calling convention.
This could use the hints from the EH data in the XEX. Looking specifically for
stack prolog/epilog and branches to LR.

Benefits:
- Optimized prolog/epilog generation.
- Local variables for stack storage (alloca/etc) instead of user memory.
- Better return detection and fast returns.

### Indirect branches (ctr/lr)

Return path:
- In SDB see if the function follows the 'return' semantic:
  - mfspr LR / mtspr LR/CTR / bcctr -- at end?
- In codegen add a BB that is just return.
- If a block 'returns', branch to the return BB.

Tail calls:
- If in a call BB check next BB.
- If next is a return, optimize to a tail call.

Fast path:
- Every time LR would be stashed, add the value of LR (some NIA) to a lookup
  table.
- When doing an indirect branch first lookup the address in the table.
- If not found, slow path, else jump.

Slow path:
- Call out and do an SDB lookup.
- If found, return, add to lookup table, and jump.
- If not found, need new function codegen!
```

## Debugging