Increase precision in InferMutableRangesForAlias

Previously, this step just set the mutable range of any alias set including any 

mutation to the end of the last mutable range of any of the containing 
identifiers. 

This change makes it so that the ends are only updated of the ranges that end 

before the last mutation. 

Fixes #852

Author: kassens

compiler/forget/src/HIR/InferMutableRangesForAlias.ts

@@ -7,18 +7,25 @@ export function inferMutableRangesForAlias(aliases: DisjointSet<Identifier>) {
   for (const aliasSet of aliasSets) {
     // Update mutableRange.end only if the identifiers have actually been
     // mutated.
-    const haveIdentifiersBeenMutated = [...aliasSet].some(
+    const mutatingIdentifiers = [...aliasSet].filter(
       (id) => id.mutableRange.end - id.mutableRange.start > 1
     );
 
-    if (haveIdentifiersBeenMutated) {
+    if (mutatingIdentifiers.length > 0) {
       // Find final instruction which mutates this alias set.
-      const mutableRangeEnds = [...aliasSet].map((id) => id.mutableRange.end);
-      const maxMutableRangeEnd = Math.max(...mutableRangeEnds) as InstructionId;
+      let lastMutatingInstructionId = 0;
+      for (const id of mutatingIdentifiers) {
+        if (id.mutableRange.end > lastMutatingInstructionId) {
+          lastMutatingInstructionId = id.mutableRange.end;
+        }
+      }
 
-      // Update mutableRange.end for all aliases in this set.
+      // Update mutableRange.end for all aliases in this set ending before the
+      // last mutation.
       for (const alias of aliasSet) {
-        alias.mutableRange.end = maxMutableRangeEnd;
+        if (alias.mutableRange.end < lastMutatingInstructionId) {
+          alias.mutableRange.end = lastMutatingInstructionId as InstructionId;
+        }
       }
     }
   }

compiler/forget/src/__tests__/fixtures/hir/component.expect.md

@@ -37,7 +37,7 @@ function Component(props) {
 bb0:
   [1] Const mutate items$27_@0 = read props$26.items
   [2] Const mutate maxItems$28_@1 = read props$26.maxItems
-  [3] Const mutate renderedItems$29_@2[3:26] = Array []
+  [3] Const mutate renderedItems$29_@2[3:22] = Array []
   [4] Const mutate seen$30_@3[0:19] = New mutate Set$6_@3()
   [5] Const mutate $31_@4 = 0
   [6] Const mutate max$32_@5[0:7] = Call mutate [email protected](read $31_@4, read maxItems$28_@1)
@@ -71,23 +71,23 @@ bb4:
   [19] Const mutate $43_@7 = "div"
   [20] Const mutate $44_@8 = JSX <read $43_@7>{read item$10_@3}</read $43_@7>
   [21] Call mutate [email protected](read $44_@8)
-  [22] Const mutate $49_@2[3:26] = Binary read [email protected] >= read max$32_@5
-  [23] If (read $49_@2) then:bb2 else:bb10 fallthrough=bb10
+  [22] Const mutate $49_@9 = Binary read [email protected] >= read max$32_@5
+  [23] If (read $49_@9) then:bb2 else:bb10 fallthrough=bb10
 bb10:
   predecessor blocks: bb4
   [24] Goto(Continue) bb1
 bb2:
   predecessor blocks: bb4 bb1
-  [25] Const mutate count$52_@2[3:26] = read [email protected]
-  [26] Const mutate $53_@9 = "div"
-  [27] Const mutate $54_@10 = "\n      "
-  [28] Const mutate $55_@11 = "h1"
-  [29] Const mutate $56_@12 = " Items"
-  [30] Const mutate $57_@13 = JSX <read $55_@11>{freeze count$52_@2}{read $56_@12}</read $55_@11>
-  [31] Const mutate $58_@14 = "\n      "
-  [32] Const mutate $59_@15 = "\n    "
-  [33] Const mutate $60_@16 = JSX <read $53_@9>{read $54_@10}{read $57_@13}{read $58_@14}{freeze renderedItems$29_@2}{read $59_@15}</read $53_@9>
-  [34] Return read $60_@16
+  [25] Const mutate count$52_@10 = read [email protected]
+  [26] Const mutate $53_@11 = "div"
+  [27] Const mutate $54_@12 = "\n      "
+  [28] Const mutate $55_@13 = "h1"
+  [29] Const mutate $56_@14 = " Items"
+  [30] Const mutate $57_@15 = JSX <read $55_@13>{freeze count$52_@10}{read $56_@14}</read $55_@13>
+  [31] Const mutate $58_@16 = "\n      "
+  [32] Const mutate $59_@17 = "\n    "
+  [33] Const mutate $60_@18 = JSX <read $53_@11>{read $54_@12}{read $57_@15}{read $58_@16}{freeze renderedItems$29_@2}{read $59_@17}</read $53_@11>
+  [34] Return read $60_@18
 scope0 [1:2]:
  - read props$26.items
 scope1 [2:3]:
@@ -103,7 +103,7 @@ flowchart TB
     bb0_instrs["
       [1] Const mutate items$27_@0 = read props$26.items
       [2] Const mutate maxItems$28_@1 = read props$26.maxItems
-      [3] Const mutate renderedItems$29_@2[3:26] = Array []
+      [3] Const mutate renderedItems$29_@2[3:22] = Array []
       [4] Const mutate seen$30_@3[0:19] = New mutate Set$6_@3()
       [5] Const mutate $31_@4 = 0
       [6] Const mutate max$32_@5[0:7] = Call mutate [email protected](read $31_@4, read maxItems$28_@1)
@@ -145,26 +145,26 @@ flowchart TB
       [19] Const mutate $43_@7 = 'div'
       [20] Const mutate $44_@8 = JSX <read $43_@7>{read item$10_@3}</read $43_@7>
       [21] Call mutate [email protected](read $44_@8)
-      [22] Const mutate $49_@2[3:26] = Binary read [email protected] >= read max$32_@5
+      [22] Const mutate $49_@9 = Binary read [email protected] >= read max$32_@5
     "]
-    bb4_instrs --> bb4_terminal(["If (read $49_@2)"])
+    bb4_instrs --> bb4_terminal(["If (read $49_@9)"])
   end
   subgraph bb10
     bb10_terminal(["Goto"])
   end
   subgraph bb2
     bb2_instrs["
-      [25] Const mutate count$52_@2[3:26] = read [email protected]
-      [26] Const mutate $53_@9 = 'div'
-      [27] Const mutate $54_@10 = '\n      '
-      [28] Const mutate $55_@11 = 'h1'
-      [29] Const mutate $56_@12 = ' Items'
-      [30] Const mutate $57_@13 = JSX <read $55_@11>{freeze count$52_@2}{read $56_@12}</read $55_@11>
-      [31] Const mutate $58_@14 = '\n      '
-      [32] Const mutate $59_@15 = '\n    '
-      [33] Const mutate $60_@16 = JSX <read $53_@9>{read $54_@10}{read $57_@13}{read $58_@14}{freeze renderedItems$29_@2}{read $59_@15}</read $53_@9>
+      [25] Const mutate count$52_@10 = read [email protected]
+      [26] Const mutate $53_@11 = 'div'
+      [27] Const mutate $54_@12 = '\n      '
+      [28] Const mutate $55_@13 = 'h1'
+      [29] Const mutate $56_@14 = ' Items'
+      [30] Const mutate $57_@15 = JSX <read $55_@13>{freeze count$52_@10}{read $56_@14}</read $55_@13>
+      [31] Const mutate $58_@16 = '\n      '
+      [32] Const mutate $59_@17 = '\n    '
+      [33] Const mutate $60_@18 = JSX <read $53_@11>{read $54_@12}{read $57_@15}{read $58_@16}{freeze renderedItems$29_@2}{read $59_@17}</read $53_@11>
     "]
-    bb2_instrs --> bb2_terminal(["Return read $60_@16"])
+    bb2_instrs --> bb2_terminal(["Return read $60_@18"])
   end
 
   %% Jumps

compiler/forget/src/__tests__/fixtures/hir/issue852.expect.md

@@ -0,0 +1,61 @@
+
+## Input
+
+```javascript
+function Component(c) {
+  let x = { c };
+  mutate(x);
+  let a = x;
+  let b = a;
+}
+
+```
+
+## HIR
+
+```
+bb0:
+  [1] Const mutate x$7_@0[0:3] = Object { c: read c$6 }
+  [2] Call mutate mutate$3_@0(mutate x$7_@0)
+  [3] Const mutate a$8_@1 = read x$7_@0
+  [4] Const mutate b$9_@2 = read a$8_@1
+  [5] Return
+scope1 [3:4]:
+ - read x$7_@0
+scope2 [4:5]:
+ - read a$8_@1
+```
+
+### CFG
+
+```mermaid
+flowchart TB
+  %% Basic Blocks
+  subgraph bb0
+    bb0_instrs["
+      [1] Const mutate x$7_@0[0:3] = Object { c: read c$6 }
+      [2] Call mutate mutate$3_@0(mutate x$7_@0)
+      [3] Const mutate a$8_@1 = read x$7_@0
+      [4] Const mutate b$9_@2 = read a$8_@1
+    "]
+    bb0_instrs --> bb0_terminal(["Return"])
+  end
+
+  %% Jumps
+  %% empty
+```
+
+## Code
+
+```javascript
+function Component$0(c$6) {
+  const x$7 = {
+    c: c$6,
+  };
+  mutate$3(x$7);
+  const a$8 = x$7;
+  const b$9 = a$8;
+}
+
+```
+      

compiler/forget/src/__tests__/fixtures/hir/issue852.js

@@ -0,0 +1,6 @@
+function Component(c) {
+  let x = { c };
+  mutate(x);
+  let a = x;
+  let b = a;
+}

compiler/forget/src/__tests__/fixtures/hir/ssa-complex-multiple-if.expect.md

@@ -21,14 +21,14 @@ function foo() {
 
 ```
 bb0:
-  [1] Let mutate x$7_@0[1:14] = 1
+  [1] Let mutate x$7_@0[1:13] = 1
   [2] Const mutate y$8_@1 = 2
   [3] Const mutate $9_@2 = 2
   [4] Const mutate $10_@3 = Binary read y$8_@1 === read $9_@2
   [5] If (read $10_@3) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
-  [6] Reassign mutate x$7_@0[1:14] = 3
+  [6] Reassign mutate x$7_@0[1:13] = 3
   [7] Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
@@ -37,18 +37,20 @@ bb1:
   [10] If (read $14_@5) then:bb4 else:bb3 fallthrough=bb3
 bb4:
   predecessor blocks: bb1
-  [11] Reassign mutate x$7_@0[1:14] = 5
+  [11] Reassign mutate x$7_@0[1:13] = 5
   [12] Goto bb3
 bb3:
   predecessor blocks: bb4 bb1
-  [13] Const mutate y$18_@0[1:14] = read x$7_@0
+  [13] Const mutate y$18_@6 = read x$7_@0
   [14] Return
 scope3 [4:5]:
  - read y$8_@1
  - read $9_@2
 scope5 [9:10]:
  - read y$8_@1
  - read $12_@4
+scope6 [13:14]:
+ - read x$7_@0
 ```
 
 ### CFG
@@ -58,7 +60,7 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate x$7_@0[1:14] = 1
+      [1] Let mutate x$7_@0[1:13] = 1
       [2] Const mutate y$8_@1 = 2
       [3] Const mutate $9_@2 = 2
       [4] Const mutate $10_@3 = Binary read y$8_@1 === read $9_@2
@@ -67,7 +69,7 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [6] Reassign mutate x$7_@0[1:14] = 3
+      [6] Reassign mutate x$7_@0[1:13] = 3
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
@@ -80,13 +82,13 @@ flowchart TB
   end
   subgraph bb4
     bb4_instrs["
-      [11] Reassign mutate x$7_@0[1:14] = 5
+      [11] Reassign mutate x$7_@0[1:13] = 5
     "]
     bb4_instrs --> bb4_terminal(["Goto"])
   end
   subgraph bb3
     bb3_instrs["
-      [13] Const mutate y$18_@0[1:14] = read x$7_@0
+      [13] Const mutate y$18_@6 = read x$7_@0
     "]
     bb3_instrs --> bb3_terminal(["Return"])
   end

compiler/forget/src/__tests__/fixtures/hir/ssa-complex-single-if.expect.md

@@ -18,22 +18,24 @@ function foo() {
 
 ```
 bb0:
-  [1] Let mutate x$5_@0[1:9] = 1
+  [1] Let mutate x$5_@0[1:8] = 1
   [2] Const mutate y$6_@1 = 2
   [3] Const mutate $7_@2 = 2
   [4] Const mutate $8_@3 = Binary read y$6_@1 === read $7_@2
   [5] If (read $8_@3) then:bb2 else:bb1 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
-  [6] Reassign mutate x$5_@0[1:9] = 3
+  [6] Reassign mutate x$5_@0[1:8] = 3
   [7] Goto bb1
 bb1:
   predecessor blocks: bb2 bb0
-  [8] Const mutate y$11_@0[1:9] = read x$5_@0
+  [8] Const mutate y$11_@4 = read x$5_@0
   [9] Return
 scope3 [4:5]:
  - read y$6_@1
  - read $7_@2
+scope4 [8:9]:
+ - read x$5_@0
 ```
 
 ### CFG
@@ -43,7 +45,7 @@ flowchart TB
   %% Basic Blocks
   subgraph bb0
     bb0_instrs["
-      [1] Let mutate x$5_@0[1:9] = 1
+      [1] Let mutate x$5_@0[1:8] = 1
       [2] Const mutate y$6_@1 = 2
       [3] Const mutate $7_@2 = 2
       [4] Const mutate $8_@3 = Binary read y$6_@1 === read $7_@2
@@ -52,13 +54,13 @@ flowchart TB
   end
   subgraph bb2
     bb2_instrs["
-      [6] Reassign mutate x$5_@0[1:9] = 3
+      [6] Reassign mutate x$5_@0[1:8] = 3
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
   subgraph bb1
     bb1_instrs["
-      [8] Const mutate y$11_@0[1:9] = read x$5_@0
+      [8] Const mutate y$11_@4 = read x$5_@0
     "]
     bb1_instrs --> bb1_terminal(["Return"])
   end

compiler/forget/src/__tests__/fixtures/hir/ssa-simple-phi.expect.md

@@ -23,25 +23,27 @@ bb0:
   [1] Const mutate y$5_@0 = 2
   [2] Const mutate $6_@1 = 1
   [3] Const mutate $7_@2 = Binary read y$5_@0 > read $6_@1
-  [4] Let mutate y$8_@3[4:10] = undefined
+  [4] Let mutate y$8_@3[4:9] = undefined
   [4] If (read $7_@2) then:bb2 else:bb3 fallthrough=bb1
 bb2:
   predecessor blocks: bb0
-  [5] Reassign mutate y$8_@3[4:10] = 1
+  [5] Reassign mutate y$8_@3[4:9] = 1
   [6] Goto bb1
 bb3:
   predecessor blocks: bb0
-  [7] Reassign mutate y$8_@3[4:10] = 2
+  [7] Reassign mutate y$8_@3[4:9] = 2
   [8] Goto bb1
 bb1:
   predecessor blocks: bb2 bb3
-  [9] Const mutate x$11_@3[4:10] = read y$8_@3
+  [9] Const mutate x$11_@4 = read y$8_@3
   [10] Return
 scope2 [3:4]:
  - read y$5_@0
  - read $6_@1
-scope3 [4:10]:
+scope3 [4:9]:
  - read $7_@2
+scope4 [9:10]:
+ - read y$8_@3
 ```
 
 ### CFG
@@ -54,25 +56,25 @@ flowchart TB
       [1] Const mutate y$5_@0 = 2
       [2] Const mutate $6_@1 = 1
       [3] Const mutate $7_@2 = Binary read y$5_@0 > read $6_@1
-      [4] Let mutate y$8_@3[4:10] = undefined
+      [4] Let mutate y$8_@3[4:9] = undefined
     "]
     bb0_instrs --> bb0_terminal(["If (read $7_@2)"])
   end
   subgraph bb2
     bb2_instrs["
-      [5] Reassign mutate y$8_@3[4:10] = 1
+      [5] Reassign mutate y$8_@3[4:9] = 1
     "]
     bb2_instrs --> bb2_terminal(["Goto"])
   end
   subgraph bb3
     bb3_instrs["
-      [7] Reassign mutate y$8_@3[4:10] = 2
+      [7] Reassign mutate y$8_@3[4:9] = 2
     "]
     bb3_instrs --> bb3_terminal(["Goto"])
   end
   subgraph bb1
     bb1_instrs["
-      [9] Const mutate x$11_@3[4:10] = read y$8_@3
+      [9] Const mutate x$11_@4 = read y$8_@3
     "]
     bb1_instrs --> bb1_terminal(["Return"])
   end