which pass of SSA will transform a ssa.Value(op=OpPhi) phi operations to a normal(not phi operations)?

[xie cui]

as we know, SSA has phi function, but the output of go tool compile -S xxx.go which do not contains a phi instruction. so i am trying to find out which SSA pass will transform a phi Op ssa.Value to normal ops?

[Keith Randall]

The regalloc pass does that. It ensures that all the inputs and the output of a phi are all in the same register (or memory location), so the phi becomes a no-op.

The regalloc pass doesn't actually remove the phi, though. Removal is actually in genssa in cmd/compile/internal/gc/ssa.go. Look for CheckLoweredPhi, which makes sure that the above statement is actually correct for all phis.