llvm dev - Nov 2021 - Function register clobber propagation

Hi all,

Does LLVM currently have any way to exploit known register usage of
already-compiled callee functions within a module to reduce register pressure in
calling functions? GCC does this, but I haven't seen any sign of this being
done (having checked on a couple of different target architectures), and
can't find any mention of such optimisation in the source.

Have I overlooked something? Or is there a rationale for not attempting this?
(Such as limiting potential parallelism in compiling a module)

Thanks!

--
Colin
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There is at least some minimal support for this, see
CodeGen/RegUsageInfoPropagate.cpp (and related). This interprocedural register
allocation is enabled with "-enable-ipra".
________________________________
From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Colin
McEwan via llvm-dev <llvm-dev at lists.llvm.org>
Sent: Tuesday, November 30, 2021 9:26 AM
To: llvm-dev at lists.llvm.org <llvm-dev at lists.llvm.org>
Subject: [llvm-dev] Function register clobber propagation

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Hi all,



Does LLVM currently have any way to exploit known register usage of
already-compiled callee functions within a module to reduce register pressure in
calling functions? GCC does this, but I haven’t seen any sign of this being done
(having checked on a couple of different target architectures), and can’t find
any mention of such optimisation in the source.



Have I overlooked something? Or is there a rationale for not attempting this?
(Such as limiting potential parallelism in compiling a module)



Thanks!



--

Colin

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