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TODO update.

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Ben Vanik 2013-01-25 01:01:11 -08:00
parent ebda245773
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@ -39,6 +39,18 @@ Overflow bits can be set via the intrinsics:
It'd be nice to avoid doing this unless absolutely required. The SDB could 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. walk functions to see if they ever read or branch on the SO bit of things.
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.
`@llvm.expect.i32`/`.i64` could be used with the BH bits in branches to `@llvm.expect.i32`/`.i64` could be used with the BH bits in branches to
indicate expected values. indicate expected values.