[PATCH] D68408: [InstCombine] Negator - sink sinkable negations

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp:180
+  }
+  case Instruction::SDiv:
+    // `sdiv` is negatible if divisor is not undef/INT_MIN/1.
----------------
nikic wrote:
> Noticed while looking through the tramp3d-v4 diff: This should be behind a one-use check, to avoid duplicating expensive division instructions.
I was hesitant about this one indeed, it isn't a typo that one-use check has gone away here,
because we //generally// consider only instruction count.

@spatel thoughts?

But the main, bigger question this touches is:
"but what if all the uses would get negated by us?
In future, can we somehow sanely model the whole negatible tree,
not giving up at non-single-use instructions,
but defer that to after we've finished building new tree?"




Repository:
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  https://reviews.llvm.org/D68408/new/

https://reviews.llvm.org/D68408