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    • Keith Randall's avatar
      cmd/compile: don't let spills clobber arguments · 7eaa8efb
      Keith Randall authored
      The compiler allows code to have multiple differently-typed views of a
      single argument. For instance, if we have
      
      func f(x float64) {
         y := *(*int64)(unsafe.Pointer(&x))
         ...
      }
      
      Then in SSA we get two OpArg ops, one with float64 type and one with
      int64 type.
      
      The compiler will try to reuse argument slots for spill slots. It
      checks that the argument slot is dead by consulting an interference
      graph.
      
      When building the interference graph, we normally ignore cross-type
      edges because the values on either end of that edge can't be allocated
      to the same slot. (This is just a space-saving optimization.) This
      rule breaks down when one of the values is an argument, because of the
      multiple views described above. If we're spilling a float64, it is not
      enough that the float64 version of x is dead; the int64 version of x
      has to be dead also.
      
      Remove the optimization of not recording interference edges if types
      don't match. That optimization is incorrect if one of the values
      connected by the edge is an argument.
      
      Fixes #23522
      
      Change-Id: I361f85d80fe3bc7249014ca2c3ec887c3dc30271
      Reviewed-on: https://go-review.googlesource.com/89335
      Run-TryBot: Keith Randall <khr@golang.org>
      Reviewed-by: default avatarDavid Chase <drchase@google.com>
      TryBot-Result: Gobot Gobot <gobot@golang.org>
      7eaa8efb