[llvm-dev] the root cause is CP, was: A tagged architecture, the elephant in the undef / poison room

Sanjoy Das via llvm-dev llvm-dev at lists.llvm.org
Tue Jun 20 00:23:36 PDT 2017

Hi Peter,

On Mon, Jun 19, 2017 at 11:59 PM, Peter Lawrence
<peterl95124 at sbcglobal.net> wrote:
> I am trying to force this issue because when I challenge folks to question
> their assumptions regarding CSE’ing and CP’ing of “undef” all I get back
> is a recitation of the usual catechism on the subject. I can’t get them
> to think outside the box without this example of the consequences
> of those assumptions. Unfortunately so far no one has responded to it.
> The VP of engineering at my last company had a way of bringing
> clarity to issues like this, he said now that robotic surgery is
> becoming a reality do you want the compiler to do this if it is being
> used to compile the robot software and you are scheduled for
> surgery.

Then don't use C or C++ for such systems?

> I also believe that the C-standard is flawed in that it uses the

This (and what follows) seems off topic -- I thought we were
discussing the semantics of LLVM IR, not C.  As I've said in my
previous email, LLVM IR semantics is not directly related to the
semantics of C.  You can implement a safe programming language (like
Java or Python) in LLVM IR.  This is covered in the paper in section

-- Sanjoy

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