cranelift: simplify fneg(fneg(x)) to x (#6034)

2023-03-16 22:14:12 +00:00
parent dccc2d6269
commit d479951469
2 changed files with 12 additions and 0 deletions
--- a/cranelift/codegen/src/opts/algebraic.isle
+++ b/cranelift/codegen/src/opts/algebraic.isle
@@ -527,6 +527,9 @@
 ;; with the `bitselect` instruction, but the pattern is a bit more complicated
 ;; due to most bitselects-over-floats having bitcasts.

+;; fneg(fneg(x)) == x.
+(rule (simplify (fneg ty (fneg ty x))) (subsume x))
+
 ;; If both of the multiplied arguments to an `fma` are negated then remove
 ;; both of them since they cancel out.
 (rule (simplify (fma ty (fneg ty x) (fneg ty y) z))