llvm dev - Jul 2014 - [LLVMdev] Getting SELECT_CC and BR_CC DAG nodes

Hello,

 

I'd like to write some unit tests which verifies SELECT_CC and BR_CC
lowering for ARM target, but I'm almost completely unfamiliar with
llvm/Target. How can I get this nodes in DAG?

Thanks.

 

--

Kind regards, Dmitry Borisenkov

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Hello,

 

I figure out by myself how to generate select_cc. I've written simple C
code: 

int f(int a) {

  return (a != 0) ? 0 : 1;

}

generate ir from it

and got select_cc node with llc -view-legalize-dags. But I got it almost
randomly: I saw comment in the sources that a ? b : c corresponds somehow
with select_cc and then customizing constness of parameters gives me node I
needed. It's low priority by now - I got what I wanted but I'll be
grateful
if somebody answer me: Does any better algorithm of figuring out how to
generate specific DAG node exists? Thank you.

 

--

Kind regards, Dmitry Borisenkov

 

 

From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On
Behalf Of Dmitry Borisenkov
Sent: Monday, July 14, 2014 5:58 PM
To: llvmdev at cs.uiuc.edu
Subject: [LLVMdev] Getting SELECT_CC and BR_CC DAG nodes

 

Hello,

 

I'd like to write some unit tests which verifies SELECT_CC and BR_CC
lowering for ARM target, but I'm almost completely unfamiliar with
llvm/Target. How can I get this nodes in DAG?

Thanks.

 

--

Kind regards, Dmitry Borisenkov

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> Does any better algorithm of figuring out how to generate specific DAG node
exists?
Not really, I'm afraid. Some suggestions, in order of desperation:

+ Read include/llvm/CodeGen/ISDOpcodes.h and write IR that would
produce the node as described.
+ Scan through SelectionDAGBuilder.cpp and/or the combiner &
legalizers, trying to work out why they're formed.
+ Put an assert somewhere definitely on the path and run "make check".
New failures will contain IR exercising the node.
+ Read files in step 2 with a fine tooth comb, cursing the person who
added a node without any tests.

Cheers.

Tim.