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Omit the ret slot alloca when it's not needed #8238

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pcwalton opened this issue Aug 2, 2013 · 2 comments
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Omit the ret slot alloca when it's not needed #8238

pcwalton opened this issue Aug 2, 2013 · 2 comments
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A-codegen Area: Code generation I-slow Issue: Problems and improvements with respect to performance of generated code.

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@pcwalton
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pcwalton commented Aug 2, 2013

Clang does not always emit an alloca for the ret slot; we likewise shouldn't.
@Aatch
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Aatch commented Aug 3, 2013

@pcwalton could you elaborate? When does clang not do it? (Just trying to make contributor's lives easier)

@dotdash
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dotdash commented Aug 3, 2013

I have implemented what clang does in dotdash@dda1467 but need to clean the thing up.

@dotdash dotdash mentioned this issue Aug 3, 2013
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bors added a commit that referenced this issue Aug 10, 2013
@bors
auto merge of #8270 : dotdash/rust/ret_alloca_elim, r=pcwalton
e70aac5 
When there is only a single store to the ret slot that dominates the
load that gets the value for the "ret" instruction, we can elide the
ret slot and directly return the operand of the dominating store
instruction. This is the same thing that clang does, except for a
special case that doesn't seem to affect us.

Fixes #8238
@bors bors closed this as completed in 4b74b8d Aug 10, 2013
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A-codegen Area: Code generation I-slow Issue: Problems and improvements with respect to performance of generated code.
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Elide unnecessary ret slot allocas dotdash/rust
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@pcwalton @dotdash @Aatch and others