[PATCH] D101191: [InstCombine] Fully disable select to and/or i1 folding

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added inline comments.


================
Comment at: llvm/test/Transforms/PhaseOrdering/unsigned-multiply-overflow-check.ll:20
 
+; FIXME: noundef should be attached to args
 define i1 @will_not_overflow(i64 %arg, i64 %arg1) {
----------------
aqjune wrote:
> spatel wrote:
> > Any ideas about what it will take to get those argument attributes for the C++ source example shown in the code comment?
> > 
> > SDAG is still going to convert the `select` to `and`, so we can probably avoid regressions by replicating InstSimplify's omitCheckForZeroBeforeMulWithOverflow() as a DAG combine. Let me know if I should do that.
> I promised to do the patch at D82317, but these days I'm occupied with other things, so it might not be a recent future (not in a month at least)...
> 
> I think it is a good chance to use freeze here: We can add
> ```
> %cond = icmp ne %x, 0
> %v = call @llvm.umul.with.overflow(%x, %y)
> %ov = extractvalue %v, 1
> %res = select i1 %cond, %ov, false
>   =>
> %y.fr = freeze %y
> %v = call @llvm.umul.with.overflow(%x, %y.fr)
> %ov = extractvalue %v, 1
> %res = %ov
> ```
> into CodeGenPrepare.
> What do you think? CodeGenPrepare is already using freeze for a few transformations.
Alive2 proof: https://alive2.llvm.org/ce/z/zgPUGT


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https://reviews.llvm.org/D101191