Test case showing reassignment block scoping problem
This demonstrates a situation we don't handle well today. The basic structure is that you have some variable defined at the top level, then some control flow like if/switch where _all_ branches reassign the variable, then some code after that references the resulting phi node: ```javascript let x1; // ... mutate/read x1 if (cond) { x2 = {}; } else { x3 = {}; } x4 = phi(x2, x3); ``` We currently group x3, x3, and x4 into a scope together, but note that...there's no `let` declaration for any of those! This means that it looks like the scope for x2 and x3 start in the consequent/alternate, but the true scope spans from before-after the if. I'm inclined to say that LeaveSSA should run _before_ scope analysis, and produce something like the following in this case: ```javascript let x1; // ...mutate/read x1 let x2; // new variable declaration for the new version of x if (cond) { x2 = {}; } else { x2 = {}; } x2; ``` This then allows us to construct a correct range for x2, which starts in the other block.
Joe Savona committed
Nov 22, 2022 at 10:42 UTC
d2e5c31fc66aba93bd63616c529a6df723033ea1
2 files changed
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compiler/forget/src/__tests__/fixtures/hir/reassignment-separate-scopes.expect.md
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+
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+## Input
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+
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+```javascript
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+function foo(a, b, c) {
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+ let x = [];
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+ if (a) {
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+ x.push(a);
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+ }
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+ let y = <div>{x}</div>;
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+
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+ switch (b) {
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+ case 0: {
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+ x = [];
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+ x.push(b);
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+ break;
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+ }
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+ default: {
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+ x = [];
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+ x.push(c);
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+ }
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+ }
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+ return (
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+ <div>
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+ {y}
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+ {x}
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+ </div>
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+ );
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+}
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+
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+```
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+
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+## HIR
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+
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+```
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+bb0:
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+ [1] Let mutate x$4_@0[1:5] = Array []
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+ [2] If (read a$1) then:bb2 else:bb1
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+bb2:
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+ predecessor blocks: bb0
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+ [3] Call mutate x$4_@0.push(read a$1)
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+ [4] Goto bb1
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+bb1:
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+ predecessor blocks: bb2 bb0
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+ [5] Const mutate $6_@1 = "div"
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+ [6] Let mutate y$5_@2 = JSX <read $6_@1>{freeze x$4_@0}</read $6_@1>
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+ [7] Const mutate $7_@4[7:14] = 0
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+ [8] Switch (read b$2)
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+ Case read $7_@4: bb5
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+ Default: bb4
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+bb5:
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+ predecessor blocks: bb1
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+ [9] Reassign mutate x$4_@4[7:14] = Array []
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+ [10] Call mutate x$4_@4.push(read b$2)
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+ [11] Goto bb3
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+bb4:
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+ predecessor blocks: bb1
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+ [12] Reassign mutate x$4_@4[7:14] = Array []
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+ [13] Call mutate x$4_@4.push(read c$3)
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+ [14] Goto bb3
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+bb3:
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+ predecessor blocks: bb5 bb4
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+ [15] Const mutate $8_@5 = "div"
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+ [16] Const mutate $9_@6 = "\n "
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+ [17] Const mutate $10_@7 = "\n "
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+ [18] Const mutate $11_@8 = "\n "
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+ [19] Const mutate $12_@9 = JSX <read $8_@5>{read $9_@6}{read y$5_@2}{read $10_@7}{freeze x$4_@4}{read $11_@8}</read $8_@5>
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+ [20] Return read $12_@9
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+```
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+
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+### CFG
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+
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+```mermaid
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+flowchart TB
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+ %% Basic Blocks
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+ subgraph bb0
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+ bb0_instrs["
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+ [1] Let mutate x$4_@0[1:5] = Array []
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+ "]
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+ bb0_instrs --> bb0_terminal(["If (read a$1)"])
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+ end
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+ subgraph bb2
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+ bb2_instrs["
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+ [3] Call mutate x$4_@0.push(read a$1)
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+ "]
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+ bb2_instrs --> bb2_terminal(["Goto"])
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+ end
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+ subgraph bb1
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+ bb1_instrs["
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+ [5] Const mutate $6_@1 = 'div'
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+ [6] Let mutate y$5_@2 = JSX <read $6_@1>{freeze x$4_@0}</read $6_@1>
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+ [7] Const mutate $7_@4[7:14] = 0
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+ "]
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+ bb1_instrs --> bb1_terminal(["Switch (read b$2)"])
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+ end
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+ subgraph bb5
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+ bb5_instrs["
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+ [9] Reassign mutate x$4_@4[7:14] = Array []
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+ [10] Call mutate x$4_@4.push(read b$2)
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+ "]
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+ bb5_instrs --> bb5_terminal(["Goto"])
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+ end
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+ subgraph bb4
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+ bb4_instrs["
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+ [12] Reassign mutate x$4_@4[7:14] = Array []
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+ [13] Call mutate x$4_@4.push(read c$3)
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+ "]
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+ bb4_instrs --> bb4_terminal(["Goto"])
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+ end
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+ subgraph bb3
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+ bb3_instrs["
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+ [15] Const mutate $8_@5 = 'div'
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+ [16] Const mutate $9_@6 = '\n '
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+ [17] Const mutate $10_@7 = '\n '
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+ [18] Const mutate $11_@8 = '\n '
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+ [19] Const mutate $12_@9 = JSX <read $8_@5>{read $9_@6}{read y$5_@2}{read $10_@7}{freeze x$4_@4}{read $11_@8}</read $8_@5>
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+ "]
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+ bb3_instrs --> bb3_terminal(["Return read $12_@9"])
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+ end
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+
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+ %% Jumps
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+ bb0_terminal -- "then" --> bb2
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+ bb0_terminal -- "else" --> bb1
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+ bb2_terminal --> bb1
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+ bb1_terminal -- "read $7_@4" --> bb5
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+ bb1_terminal -- "default" --> bb4
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+ bb1_terminal -- "fallthrough" --> bb3
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+ bb5_terminal --> bb3
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+ bb4_terminal --> bb3
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+
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+```
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+
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+## Code
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+
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+```javascript
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+function foo$0(a$1, b$2, c$3) {
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+ let x$4 = [];
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+ bb1: if (a$1) {
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+ x$4.push(a$1);
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+ }
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+
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+ let y$5 = <div>{x$4}</div>;
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+
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+ bb3: switch (b$2) {
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+ case 0: {
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+ x$4 = [];
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+ x$4.push(b$2);
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+ break bb3;
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+ }
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+
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+ default: {
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+ x$4 = [];
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+ x$4.push(c$3);
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+ }
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+ }
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+
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+ return (
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+ <div>
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+ {y$5}
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+ {x$4}
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+ </div>
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+ );
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+}
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+
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+```
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+
\ No newline at end of file
compiler/forget/src/__tests__/fixtures/hir/reassignment-separate-scopes.js
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+function foo(a, b, c) {
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+ let x = [];
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+ if (a) {
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+ x.push(a);
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+ }
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+ let y = <div>{x}</div>;
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+
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+ switch (b) {
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+ case 0: {
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+ x = [];
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+ x.push(b);
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+ break;
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+ }
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+ default: {
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+ x = [];
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+ x.push(c);
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+ }
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+ }
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+ return (
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+ <div>
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+ {y}
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+ {x}
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+ </div>
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+ );
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+}