[LLVMdev] 32 bit boolean results

Villmow, Micah Micah.Villmow at amd.com
Tue Nov 18 13:56:01 PST 2008

Sorry, accidently hit send hotkeys before finishing email.


I am still trying to figure out why my comparison instructions are being
modified and overall producing incorrect results.


The IR produces correct results, but my backend does not and the only
thing I can think of is that the IR is treating the Booleans as i1 and
therefore either and'ing or xor'ing the results of my comparison with
the value 1. 


This is causing the IR after running opt to be correct, but when it hits
my backend, there are some changes that generate something weird.

int gID = width;

const int idx = gID % 64;

const int idy = gID / 64;

pv[gID] = 0;

if( idy > 63 && idx > 0 )





generates conditionals :

            ult r1043.x, 63, r1026.x

            ilt r1041.x, r1039.x, 1

            and r1041.x, r1041.x, r1043.x

            if_logicalz r1041.x

             //write to pv


which is C for 

if ((63 < idy && idx < 1) == 0) {



I have no clue how the 1 gets put in there but being able to stop the
xor/and instructions from being inserted and modifying my comparison
instructions would help me pinpoint where the error is.





From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
On Behalf Of Chris Lattner
Sent: Tuesday, November 18, 2008 1:00 PM
To: LLVM Developers Mailing List
Subject: Re: [LLVMdev] 32 bit boolean results



On Nov 18, 2008, at 11:24 AM, Villmow, Micah wrote:

Is there a way to tell LLVM to treat Boolean results as 32bit values
instead of 1 bit values?


LLVM IR doesn't have a concept of C level booleans.  What problem are
you trying to solve?






Micah Villmow

Systems Engineer

Advanced Technology & Performance

Advanced Micro Devices Inc.

4555 Great America Pkwy,

Santa Clara, CA. 95054

P: 408-572-6219

F: 408-572-6596


LLVM Developers mailing list
LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu


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