6817210edf
HMUL is commutative. However, it has asymmetric register requirements. There are existing rewrite rules to place arguments in preferable slots. Due to a bug, the existing rulegen commutativity engine doesn't generate the commuted form of the HMUL rules. The commuted form of those rewrite rules cause infinite loops. In order to fix the rulegen commutativity bug, we need to choose between eliminating those rewrite rules and marking HMUL ops as not commutative. This change chooses the latter, since doing so yields better optimization results on std+cmd. Removing the rewrite rules yields only text size regressions: file before after Δ % runtime.s 477257 477269 +12 +0.003% time.s 83552 83612 +60 +0.072% encoding/asn1.s 57378 57382 +4 +0.007% cmd/go/internal/modfetch/codehost.s 89822 89829 +7 +0.008% cmd/internal/test2json.s 9459 9466 +7 +0.074% cmd/go/internal/test.s 57665 57678 +13 +0.023% Marking HMUL as not commutative actually yields (mostly) improvements: file before after Δ % runtime.s 477257 477247 -10 -0.002% math.s 35985 35992 +7 +0.019% strconv.s 53486 53462 -24 -0.045% syscall.s 82483 82446 -37 -0.045% time.s 83552 83561 +9 +0.011% os.s 52691 52684 -7 -0.013% archive/zip.s 42285 42272 -13 -0.031% encoding/asn1.s 57378 57329 -49 -0.085% encoding/base64.s 12156 12094 -62 -0.510% net.s 296286 296276 -10 -0.003% encoding/base32.s 9720 9658 -62 -0.638% net/http.s 560931 560907 -24 -0.004% net/smtp.s 14421 14411 -10 -0.069% cmd/vendor/golang.org/x/sys/unix.s 74307 74266 -41 -0.055% The regressions are minor, and are in functions math.cbrt, time.Time.String, and time.Date. Change-Id: I9f6d9ee71654e5b70381cac77b0ac26011f4ea12 Reviewed-on: https://go-review.googlesource.com/c/go/+/213701 Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com> Reviewed-by: Keith Randall <khr@golang.org> |
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