llvm dev - Dec 2008 - [LLVMdev] 32bit math being promoted to 64 bit

What optimization pass promotes 32 bit math operations to 64 bit
operations so I can disable it? I have code that works fine with
optimizations turned off but fails with it turned on because of this
stage.

 

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

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20081204/97fe5239/attachment.html>

On Dec 4, 2008, at 8:58 AM, Villmow, Micah wrote:
> What optimization pass promotes 32 bit math operations to 64 bit  
> operations so I can disable it? I have code that works fine with  
> optimizations turned off but fails with it turned on because of this  
> stage.
>
Do you have a testcase?  An .ll file with no 64-bit operations, and  
one optimization pass that introduces them?

-Chris

-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20081204/f7b20800/attachment.html>

On Thu, Dec 4, 2008 at 7:08 PM, Chris Lattner <clattner at apple.com>
wrote:
>
> On Dec 4, 2008, at 8:58 AM, Villmow, Micah wrote:
>
> What optimization pass promotes 32 bit math operations to 64 bit operations
> so I can disable it? I have code that works fine with optimizations turned
> off but fails with it turned on because of this stage.
>
>
> Do you have a testcase?  An .ll file with no 64-bit operations, and one
> optimization pass that introduces them?
Sounds a lot like the issue I reported in PR 3101.

Can you run your bitcode through opt -instcombine and check for promotions?

Greetings,

Tilmann

I've attached the original ll file and the result of doing

llvm-as < test_fc_27.ll | opt -std-compile-opts > test_fc_27-opt.bc

llvm-dis test_fc_27-opt.bc

 

This is very problematic as 64 bit integer operations are software
emulated and I would rather not have them generated unless explicitly
requested by the programmer.

 

________________________________

From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
On Behalf Of Chris Lattner
Sent: Thursday, December 04, 2008 10:08 AM
To: LLVM Developers Mailing List
Subject: Re: [LLVMdev] 32bit math being promoted to 64 bit

 

 

On Dec 4, 2008, at 8:58 AM, Villmow, Micah wrote:





What optimization pass promotes 32 bit math operations to 64 bit
operations so I can disable it? I have code that works fine with
optimizations turned off but fails with it turned on because of this
stage.

 

 

Do you have a testcase?  An .ll file with no 64-bit operations, and one
optimization pass that introduces them?

 

-Chris

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20081204/fbb41292/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: test_fc_27.ll
Type: application/octet-stream
Size: 2450 bytes
Desc: test_fc_27.ll
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20081204/fbb41292/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: test_fc_27-opt.ll
Type: application/octet-stream
Size: 1689 bytes
Desc: test_fc_27-opt.ll
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20081204/fbb41292/attachment-0001.obj>

> Do you have a testcase?  An .ll file with no 64-bit operations, and one
> optimization pass that introduces them?
It's pretty common to instcombine to expand 32 bit operations to 64
bit. See, for example, recent issue with CellSPU's 32 =>64 bit muls

-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University