[llvm-dev] HUGE constant expression generation

Friedman, Eli via llvm-dev llvm-dev at lists.llvm.org
Tue Jul 25 11:37:56 PDT 2017

On 7/25/2017 2:48 AM, Sam Parker via llvm-dev wrote:
> Hi,
> In running opt -indvars on the attached file, I see a massive constant 
> expression being generated (I stop opt once the output file grows 
> larger than 3GB). The example comes from a reduced version an LNT 
> test. I've been looking into constant folding and indvar simplify to 
> see if there's a way to limit the depth of these expressions, but I 
> haven't figured anything out.
> Could anyone shine some light into how to handle these expressions? 
> Could they be broken into multiple values? Or can we limit the 
> complexity of constant exprs?

It's a known issue that printing textual IR for constant expressions 
which have the same operand multiple times can cause an exponential 
explosion in the size of the text.  Other passes generally handle 
expressions like that without any problem, though.


Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project

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