[LLVMdev] Boolean simplification in LLVM

[Jonathan Roelofs]

On 6/17/15 10:41 AM, Hans Wennborg wrote:
> On Tue, Jun 16, 2015 at 6:57 PM, Anirudh Sivaraman <sk.anirudh at gmail.com> wrote:
>> I am trying to implement if-conversion as an LLVM pass. My reference
>> is Chapter 7 of the book ""Optimizing Compilers for Modern
>> Architectures", based on the suggestion here:
>> https://groups.google.com/d/msg/llvm-dev/FlDGnqSGbR8/eH5hO9IBbXYJ Some
>> steps in the if-conversion pass require simplification of Boolean
>> Expressions. Is this doable within the LLVM API? llvm::ConstantExpr
>> seems like the data structure to use, but I haven't found a way to
>> simplify a value represented by a ConstantExpr.
>
> Do you need simplification (e.g. "x + 0 = x") or constant folding? If
> it's the former, see include/llvm/Analysis/InstructionSimplify.h. For
> the latter, check out the functions in
> include/llvm/Analysis/ConstantFolding.h.

Kennedy/Allen's definition of Simplify() is on page 342.

AFAIK, there isn't existing infrastructure that implements that 
procedure specifically.  I'd suggest implementing it in your pass.


Cheers,

Jon

>
> Cheers,
> Hans
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-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded