[PATCH] D154953: [InstSimplify] Remove the remainder loop if we know the mask is always true

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


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Comment at: llvm/lib/Analysis/InstructionSimplify.cpp:1286
+      unsigned MaxActiveBits = Known.countMaxActiveBits();
+      if (MaxActiveBits <= RemC->logBase2())
+        return ConstantInt::getNullValue(Op0->getType());
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Allen wrote:
> nikic wrote:
> > This check looks a bit roundabout. I think what you actually want to check is that `Known.getMaxValue().ule(*RemC)`?
> I still use the **getActiveBits**  because the value of **Known.getMaxValue()** is not a power-of-two value. 
> For example, we can easily get the the ConstantRange(8, 16) from the **vscale_range(1,16)**, but then the 
> **Known = ConstantRange(8, 16)->toKnownBits()** will get the value of **Known.getMaxValue()** is 31 instead of 16,
> so I can't compare them with its value directly.
> 
> I also change the boundary test for test case **urem_vscale_range **and **urem_shl_vscale_out_of_range**
Okay, I see. Would it work if you used computeConstantRange() instead of computeKnownBits()? That should give an accurate range for vscale.


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  https://reviews.llvm.org/D154953/new/

https://reviews.llvm.org/D154953