tianshilei1992 added a comment.
I will refine some logics to set `X`, `E`, etc. to avoid more `IgnoreImpCasts`.
However, I don't know how to deal with type promotion in the condition
statement. Here we consider the following case:
if (x == e) { x = d; }
`x` and `d` can be set easily w/o need of `IgnoreImpCasts`. When it comes to
`e`, things become complicated. There are basically three cases:
1. `x` and `e` are not promoted. That is the case when `x` and `e` are of same
type, and they are both at least `int`. In this case, we don't need
`IgnoreImpCasts` here. If they are of the same with shorter representation,
such as `int16_t`, they will all be promoted, which will be mentioned later.
2. `x` is not promoted, but `e` is promoted. That is the case when `x` has
higher ranking than `e`. In this case, we should not use `IgnoreImpCasts`.
3. Both `x` and `e` are promoted. This case is very common, and it can be
further divided into following cases:
- `x` and `e` of the same type with lower ranking. For example, when `x` and
`e` are both `short`, they will be promoted to `int`. In this case, we want
`IgnoreImpCasts`.
- `x` and `e` are of different types, but they can be implicitly converted.
For example, `x` is `int`, while `e` is `short`. In this case, we don't want
`IgnoreImpCasts` because `e` is implicitly promoted to `int`, which is exactly
what we want.
I'm thinking we may want to avoid using `IgnoreImpCasts` and later create cast
if necessary. However, that may cause some unnecessary casts, at least in LLVM
IR, such as the following case:
%1 = load i8 *%e
%2 = cast to i32 %1
%3 = cast to i8 %2
cmpxchg i8 * %x, i8 %3
I'm not sure eventually `%2` and `%3` will be optimized out.
Repository:
rG LLVM Github Monorepo
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https://reviews.llvm.org/D126602/new/
https://reviews.llvm.org/D126602
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