[llvm-dev] RFC: Adding Register Calling Convention Support

[Ben Simhon, Oren via llvm-dev]

Thanks, Philip, for pointing it out.
You are correct. We have a task to add the relevant infrastructure.
Currently registers are statically defined as callee/caller saved.
In order to take into account which registers were passed as parameter we need to add relevant infrastructure.
Only then LLVM will ensure RegCall cross-compiler Interoperability.

Thanks again,
Oren

From: Philip Reames [mailto:listmail at philipreames.com]
Sent: Sunday, September 25, 2016 02:08
To: Ben Simhon, Oren <oren.ben.simhon at intel.com>; llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] RFC: Adding Register Calling Convention Support


Seems technically straight forward form the LLVM perspective.  The only complication is it looks like your callee saved register lists are influenced by the number of arguments to the functions.  I'm not sure that'll be easy to encode with the current infrastructure.

Philip

On 09/22/2016 12:07 AM, Ben Simhon, Oren via llvm-dev wrote:
Hi All,

The Register Calling Convention (RegCall) was introduced by Intel to optimize parameter transfer on function call.
This calling convention ensures that as many values as possible are passed or returned in registers.

To use RegCall, place the keyword before a function declaration. For example:
__regcall int foo (int i, int j); // Windows OS
__attribute__((regcall)) foo (int I, int j); // Linux OS and Mac OS X)

The calling convention is described in more details here:
https://software.intel.com/en-us/node/693069

We are adding support for RegCall calling convention for Clang and LLVM IR.
The first step will include the implementation for LLVM IR.

I will appreciate your comments.

Thanks,
Oren


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