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ruby--ruby/benchmark/masgn.yml

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Evaluate multiple assignment left hand side before right hand side In regular assignment, Ruby evaluates the left hand side before the right hand side. For example: ```ruby foo[0] = bar ``` Calls `foo`, then `bar`, then `[]=` on the result of `foo`. Previously, multiple assignment didn't work this way. If you did: ```ruby abc.def, foo[0] = bar, baz ``` Ruby would previously call `bar`, then `baz`, then `abc`, then `def=` on the result of `abc`, then `foo`, then `[]=` on the result of `foo`. This change makes multiple assignment similar to single assignment, changing the evaluation order of the above multiple assignment code to calling `abc`, then `foo`, then `bar`, then `baz`, then `def=` on the result of `abc`, then `[]=` on the result of `foo`. Implementing this is challenging with the stack-based virtual machine. We need to keep track of all of the left hand side attribute setter receivers and setter arguments, and then keep track of the stack level while handling the assignment processing, so we can issue the appropriate topn instructions to get the receiver. Here's an example of how the multiple assignment is executed, showing the stack and instructions: ``` self # putself abc # send abc, self # putself abc, foo # send abc, foo, 0 # putobject 0 abc, foo, 0, [bar, baz] # evaluate RHS abc, foo, 0, [bar, baz], baz, bar # expandarray abc, foo, 0, [bar, baz], baz, bar, abc # topn 5 abc, foo, 0, [bar, baz], baz, abc, bar # swap abc, foo, 0, [bar, baz], baz, def= # send abc, foo, 0, [bar, baz], baz # pop abc, foo, 0, [bar, baz], baz, foo # topn 3 abc, foo, 0, [bar, baz], baz, foo, 0 # topn 3 abc, foo, 0, [bar, baz], baz, foo, 0, baz # topn 2 abc, foo, 0, [bar, baz], baz, []= # send abc, foo, 0, [bar, baz], baz # pop abc, foo, 0, [bar, baz] # pop [bar, baz], foo, 0, [bar, baz] # setn 3 [bar, baz], foo, 0 # pop [bar, baz], foo # pop [bar, baz] # pop ``` As multiple assignment must deal with splats, post args, and any level of nesting, it gets quite a bit more complex than this in non-trivial cases. To handle this, struct masgn_state is added to keep track of the overall state of the mass assignment, which stores a linked list of struct masgn_attrasgn, one for each assigned attribute. This adds a new optimization that replaces a topn 1/pop instruction combination with a single swap instruction for multiple assignment to non-aref attributes. This new approach isn't compatible with one of the optimizations previously used, in the case where the multiple assignment return value was not needed, there was no lhs splat, and one of the left hand side used an attribute setter. This removes that optimization. Removing the optimization allowed for removing the POP_ELEMENT and adjust_stack functions. This adds a benchmark to measure how much slower multiple assignment is with the correct evaluation order. This benchmark shows: * 4-9% decrease for attribute sets * 14-23% decrease for array member sets * Basically same speed for local variable sets Importantly, it shows no significant difference between the popped (where return value of the multiple assignment is not needed) and !popped (where return value of the multiple assignment is needed) cases for attribute and array member sets. This indicates the previous optimization, which was dropped in the evaluation order fix and only affected the popped case, is not important to performance. Fixes [Bug #4443]
2021-04-21 13:49:19 -04:00
prelude: |
a = [nil] * 3
b = Class.new{attr_writer :a, :b, :c}.new
c, d, e, f = nil, nil, nil, nil
benchmark:
array2_2: "c = (a[0], a[1] = 1, 2)"
array2_3: "c = (a[0], a[1] = 1, 2, 3)"
array3_2: "c = (a[0], a[1], a[2] = 1, 2)"
array3_3: "c = (a[0], a[1], a[2] = 1, 2, 3)"
attr2_2: "c = (b.a, b.b = 1, 2)"
attr2_3: "c = (b.a, b.b = 1, 2, 3)"
attr3_2: "c = (b.a, b.b, b.c = 1, 2)"
attr3_3: "c = (b.a, b.b, b.c = 1, 2, 3)"
lvar2_2: "c = (d, e = 1, 2)"
lvar2_3: "c = (d, e = 1, 2, 3)"
lvar3_2: "c = (d, e, f = 1, 2)"
lvar3_3: "c = (d, e, f = 1, 2, 3)"
array2_2p: "(a[0], a[1] = 1, 2; nil)"
array2_3p: "(a[0], a[1] = 1, 2, 3; nil)"
array3_2p: "(a[0], a[1], a[2] = 1, 2; nil)"
array3_3p: "(a[0], a[1], a[2] = 1, 2, 3; nil)"
attr2_2p: "(b.a, b.b = 1, 2; nil)"
attr2_3p: "(b.a, b.b = 1, 2, 3; nil)"
attr3_2p: "(b.a, b.b, b.c = 1, 2; nil)"
attr3_3p: "(b.a, b.b, b.c = 1, 2, 3; nil)"
lvar2_2p: "(d, e = 1, 2; nil)"
lvar2_3p: "(d, e = 1, 2, 3; nil)"
lvar3_2p: "(d, e, f = 1, 2; nil)"
lvar3_3p: "(d, e, f = 1, 2, 3; nil)"
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