[PATCH] D64275: [InstCombine] Generalize InstCombiner::foldAndOrOfICmpsOfAndWithPow2().

[Huihui Zhang via Phabricator via llvm-commits]

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================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp:908-910
+        B = Builder.CreateLShr(
+            ConstantInt::get(Ty, APInt::getSignMask(Ty->getScalarSizeInBits())),
+            B2);
----------------
lebedev.ri wrote:
> spatel wrote:
> > lebedev.ri wrote:
> > > To be pointed out, this indeed creates an instruction while we don't know yet whether we will be able to do the fold,
> > > not great, but i think this is the smallest evil, the alternative solution would indeed be uglier..
> > Hmm...do we have a test where the temporary instruction is created, but the fold fails?
> > Last time I made that mistake, we infinite looped: the temporary instruction gets created and deleted triggering another round of combining and repeat forever.
> Oh, hmm.
Thank you for point this out! Indeed there are chances of infinite looping

see test

```
define i1 @foo(i32 %k, i32 %c1, i32 %c2) {
  %t0 = shl i32 3, %c1
  %t1 = and i32 %t0, %k
  %t2 = icmp eq i32 %t1, 0
  %t3 = shl i32 %k, %c2
  %t4 = icmp sgt i32 %t3, -1
  %or = or i1 %t2, %t4
  ret i1 %or
}

```

I am working on a solution now.



Repository:
  rL LLVM

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  https://reviews.llvm.org/D64275/new/

https://reviews.llvm.org/D64275