cmd/compile: guard the &-to-<<>> opt against small constants Converting an and-K into a pair of shifts for K that will fit in a one-byte argument is probably not an optimization, and it also interferes with other patterns that we want to see fire, like (<< (AND K)) [for small K] and bounds check elimination for masked indices. Turns out that on Intel, even 32-bit signed immediates beat the shift pair; the size reduction of tool binaries is 0.09% vs 0.07% for only the 8-bit immediates. RLH found this one working on the new/next GC. Change-Id: I2414a8de1dd58d680d18587577fbadb7ff4f67d9 Reviewed-on: https://go-review.googlesource.com/20410 Reviewed-by: Keith Randall <khr@golang.org> Run-TryBot: David Chase <drchase@google.com>
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