[PATCH] D37762: [InstCombine] Remove single use restriction from InstCombine's explicit sinking code.

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

Here's a longer version of what I saw in the benchmark i was looking at

y1 = 0;
y2 = (x & 2) ? (y1 | C1) : y1
y3 = (x & 4) ? (y2 | C2) : y2
y4 = (x & 8) ? (y3 | C3) : y3
y5 = (x & 16) ? (y4 | C4) : y4
y6 = (x & 32) ? (y5 | C5) : y5
y7 = (x & 64) ? (y6 | C6) : y6
if (x & 254) {

  y8 = (x & 128) ? (y7 | C7) : y7
  store y8 to memory

}

As you can see y7 is only used inside the if body, but we didn’t sink it. The select for y8, the (y7 | C7) for its left hand size and the (x & 128) all started output above the if (x & 254) and were pushed down because they were only needed by the store.

Is there some other pass that I should expect to sink this code so that we don't waste time decoding/executing the resulting ors and cmovs when (x & 254) is false?


https://reviews.llvm.org/D37762