Add and use eachTerminalSuccessor()

compiler/forget/src/HIR/EnterSSA.ts

@@ -2,7 +2,6 @@ import { assertExhaustive } from "../Common/utils";
 import { invariant } from "../CompilerError";
 import {
   BasicBlock,
-  BlockId,
   HIRFunction,
   Identifier,
   Instruction,
@@ -11,6 +10,7 @@ import {
 } from "./HIR";
 import { Environment } from "./HIRBuilder";
 import { printIdentifier } from "./PrintHIR";
+import { eachTerminalSuccessor } from "./visitors";
 
 type IncompletePhi = {
   oldId: Identifier;
@@ -186,7 +186,7 @@ export default function enterSSA(func: HIRFunction, env: Environment) {
     }
 
     for (const instr of block.instructions) {
-      rewriteUses(instr, builder);
+      rewriteInstructionUses(instr, builder);
 
       if (instr.lvalue != null) {
         const oldPlace = instr.lvalue.place;
@@ -200,9 +200,9 @@ export default function enterSSA(func: HIRFunction, env: Environment) {
       }
     }
 
-    const outputs = rewriteUsesAndCollectOutputs(block, builder);
-    const outputBlocks = outputs.map((id) => func.body.blocks.get(id)!);
-    for (const output of outputBlocks) {
+    rewriteTerminalOperands(block, builder);
+    for (const outputId of eachTerminalSuccessor(block.terminal)) {
+      const output = func.body.blocks.get(outputId)!;
       let count;
       if (builder.unsealedPreds.has(output)) {
         count = builder.unsealedPreds.get(output)! - 1;
@@ -218,11 +218,7 @@ export default function enterSSA(func: HIRFunction, env: Environment) {
   }
 }
 
-function rewriteUsesAndCollectOutputs(
-  block: BasicBlock,
-  builder: SSABuilder
-): Array<BlockId> {
-  const outputs: Array<BlockId> = [];
+function rewriteTerminalOperands(block: BasicBlock, builder: SSABuilder): void {
   const { terminal } = block;
   switch (terminal.kind) {
     case "return":
@@ -233,14 +229,11 @@ function rewriteUsesAndCollectOutputs(
       break;
     }
     case "goto": {
-      outputs.push(terminal.block);
       break;
     }
     case "if": {
       const { consequent, alternate } = terminal;
       terminal.test = builder.getPlace(terminal.test);
-      outputs.push(alternate);
-      outputs.push(consequent);
       break;
     }
     case "switch": {
@@ -250,7 +243,6 @@ function rewriteUsesAndCollectOutputs(
         if (case_.test) {
           case_.test = builder.getPlace(case_.test);
         }
-        outputs.push(case_.block);
       }
       break;
     }
@@ -261,11 +253,9 @@ function rewriteUsesAndCollectOutputs(
       );
     }
   }
-
-  return outputs;
 }
 
-function rewriteUses(instr: Instruction, builder: SSABuilder) {
+function rewriteInstructionUses(instr: Instruction, builder: SSABuilder) {
   const instrValue = instr.value;
 
   switch (instrValue.kind) {

compiler/forget/src/HIR/HIRBuilder.ts

@@ -19,7 +19,7 @@ import {
   Terminal,
 } from "./HIR";
 import { printInstruction } from "./PrintHIR";
-import { mapTerminalSuccessors } from "./visitors";
+import { eachTerminalSuccessor, mapTerminalSuccessors } from "./visitors";
 
 // *******************************************************************************************
 // *******************************************************************************************
@@ -512,34 +512,8 @@ function markPredecessors(func: HIR) {
 
     const { terminal } = block;
 
-    switch (terminal.kind) {
-      case "return":
-      case "throw": {
-        break;
-      }
-      case "goto": {
-        visit(terminal.block, block);
-        break;
-      }
-      case "if": {
-        const { consequent, alternate } = terminal;
-        visit(alternate, block);
-        visit(consequent, block);
-        break;
-      }
-      case "switch": {
-        const { cases } = terminal;
-        for (const case_ of [...cases]) {
-          visit(case_.block, block);
-        }
-        break;
-      }
-      default: {
-        assertExhaustive(
-          terminal,
-          `Unexpected terminal kind '${(terminal as any).kind}'`
-        );
-      }
+    for (const successor of eachTerminalSuccessor(terminal)) {
+      visit(successor, block);
     }
   }
   visit(func.entry, null);

compiler/forget/src/HIR/InferReferenceEffects.ts

@@ -16,15 +16,14 @@ import {
   InstructionValue,
   Phi,
   Place,
-  Terminal,
   ValueKind,
 } from "./HIR";
+import { printMixedHIR, printPlace, printSourceLocation } from "./PrintHIR";
 import {
   eachInstructionOperand,
   eachTerminalOperand,
-  mapTerminalSuccessors,
+  eachTerminalSuccessor,
 } from "./visitors";
-import { printMixedHIR, printPlace, printSourceLocation } from "./PrintHIR";
 
 /**
  * For every usage of a value in the given function, infers the effect or action
@@ -137,17 +136,9 @@ export default function inferReferenceEffects(fn: HIRFunction) {
       const environment = incomingEnvironment.clone();
       inferBlock(environment, block);
 
-      // TODO: add a `forEachTerminalSuccessor` helper, we don't actually want the result
-      // here
-      const _ = mapTerminalSuccessors(
-        block.terminal,
-        (nextBlockId, isFallthrough) => {
-          if (!isFallthrough) {
-            queue(nextBlockId, environment);
-          }
-          return nextBlockId;
-        }
-      );
+      for (const nextBlockId of eachTerminalSuccessor(block.terminal)) {
+        queue(nextBlockId, environment);
+      }
     }
   }
 }

compiler/forget/src/HIR/visitors.ts

@@ -129,6 +129,43 @@ export function mapTerminalSuccessors(
   }
 }
 
+/**
+ * Iterates over the successor block ids of the provided terminal. The function is called
+ * specifically for the successors that define the standard control flow, and not
+ * pseduo-successors such as fallthroughs.
+ */
+export function* eachTerminalSuccessor(terminal: Terminal): Iterable<BlockId> {
+  switch (terminal.kind) {
+    case "goto": {
+      yield terminal.block;
+      break;
+    }
+    case "if": {
+      yield terminal.consequent;
+      yield terminal.alternate;
+      break;
+    }
+    case "switch": {
+      for (const case_ of terminal.cases) {
+        yield case_.block;
+      }
+      break;
+    }
+    case "return": {
+      break;
+    }
+    case "throw": {
+      break;
+    }
+    default: {
+      assertExhaustive(
+        terminal,
+        `Unexpected terminal kind '${(terminal as any as Terminal).kind}'`
+      );
+    }
+  }
+}
+
 export function* eachTerminalOperand(terminal: Terminal): Iterable<Place> {
   switch (terminal.kind) {
     case "if": {

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

@@ -43,7 +43,7 @@ bb0:
   [6] Const mutate max$32 = Call mutate Math$8.max(read $31, read maxItems$28)
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb4 bb7
+  predecessor blocks: bb0 bb7 bb4
   If (read items$27) then:bb3 else:bb2
 bb3:
   predecessor blocks: bb1
@@ -59,8 +59,8 @@ bb9:
   [10] Const mutate $39 = Call mutate seen$30.has(mutate item$10)
   Goto bb7
 bb7:
-  predecessor blocks: bb9 bb8
-  $40: phi(bb9: $39, bb8: $37)
+  predecessor blocks: bb8 bb9
+  $40: phi(bb8: $37, bb9: $39)
   If (read $40) then:bb1 else:bb4
 bb4:
   predecessor blocks: bb7
@@ -71,7 +71,7 @@ bb4:
   [15] Const mutate $49 = Binary read renderedItems$29.length >= read max$32
   If (read $49) then:bb2 else:bb1
 bb2:
-  predecessor blocks: bb1 bb4
+  predecessor blocks: bb4 bb1
   [16] Const mutate count$52 = read renderedItems$29.length
   [17] Const mutate $53 = "div"
   [18] Const mutate $54 = "\n      "

compiler/forget/src/__tests__/fixtures/hir/conditional-break.expect.md

@@ -118,7 +118,7 @@ bb2:
   [3] Call mutate a$4.push(read props$3.c)
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
+  predecessor blocks: bb2 bb0
   [4] Call mutate a$4.push(read props$3.d)
   Return freeze a$4
 ```
@@ -218,7 +218,7 @@ bb2:
   [3] Call mutate a$4.push(read props$3.c)
   Goto bb1
 bb1:
-  predecessor blocks: bb2 bb0
+  predecessor blocks: bb0 bb2
   [4] Call mutate a$4.push(read props$3.d)
   Return freeze a$4
 ```

compiler/forget/src/__tests__/fixtures/hir/conditional-on-mutable.expect.md

@@ -75,14 +75,14 @@ bb2:
   [3] Call mutate a$7.push(read props$6.p0)
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
+  predecessor blocks: bb2 bb0
   If (read props$6.p1) then:bb4 else:bb3
 bb4:
   predecessor blocks: bb1
   [4] Call mutate b$8.push(read props$6.p2)
   Goto bb3
 bb3:
-  predecessor blocks: bb1 bb4
+  predecessor blocks: bb4 bb1
   [5] Const mutate $16 = JSX <read Foo$4 a={freeze a$7} b={freeze b$8} ></read Foo$4>
   Return read $16
 ```
@@ -120,14 +120,14 @@ bb2:
   [4] Call mutate a$9.push(read props$8.p0)
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
+  predecessor blocks: bb2 bb0
   If (read props$8.p1) then:bb4 else:bb3
 bb4:
   predecessor blocks: bb1
   [5] Call mutate b$10.push(read props$8.p2)
   Goto bb3
 bb3:
-  predecessor blocks: bb1 bb4
+  predecessor blocks: bb4 bb1
   [6] Const mutate $19 = JSX <read Foo$6 a={freeze a$9} b={freeze b$10} ></read Foo$6>
   Return read $19
 ```

compiler/forget/src/__tests__/fixtures/hir/hooks-freeze-possibly-mutable-arguments.expect.md

@@ -39,8 +39,8 @@ bb3:
   [5] Reassign mutate a$12 = Array []
   Goto bb1
 bb1:
-  predecessor blocks: bb3 bb2
-  a$14: phi(bb3: a$12, bb2: a$11)
+  predecessor blocks: bb2 bb3
+  a$14: phi(bb2: a$11, bb3: a$12)
   [6] Call read useFreeze$5(freeze a$14)
   [7] Call read useFreeze$5(read a$14)
   [8] Call mutate call$6(read a$14)

compiler/forget/src/__tests__/fixtures/hir/independent-across-if.expect.md

@@ -106,7 +106,7 @@ bb2:
   [4] Call mutate mutate$5(mutate b$10)
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
+  predecessor blocks: bb2 bb0
   [5] Const mutate $14 = JSX <read Foo$6 a={freeze a$9} b={freeze b$10} ></read Foo$6>
   Return read $14
 ```

compiler/forget/src/__tests__/fixtures/hir/interdependent-across-if.expect.md

@@ -84,7 +84,7 @@ bb2:
   [3] Call mutate foo$5(mutate a$9, mutate b$10)
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
+  predecessor blocks: bb2 bb0
   [4] Const mutate $14 = JSX <read Foo$6 a={freeze a$9} b={freeze b$10} ></read Foo$6>
   Return read $14
 ```

compiler/forget/src/__tests__/fixtures/hir/logical-expression.expect.md

@@ -34,8 +34,8 @@ bb3:
   [3] Const mutate $7 = read $5
   Goto bb1
 bb1:
-  predecessor blocks: bb3 bb2
-  $8: phi(bb3: $7, bb2: $6)
+  predecessor blocks: bb2 bb3
+  $8: phi(bb2: $6, bb3: $7)
   Return freeze $8
 ```
 
@@ -67,8 +67,8 @@ bb3:
   [3] Const mutate $7 = Call mutate g$4()
   Goto bb1
 bb1:
-  predecessor blocks: bb3 bb2
-  $8: phi(bb3: $7, bb2: $6)
+  predecessor blocks: bb2 bb3
+  $8: phi(bb2: $6, bb3: $7)
   Return freeze $8
 ```
 
@@ -102,8 +102,8 @@ bb3:
   [5] Const mutate $13 = Call mutate g$7()
   Goto bb1
 bb1:
-  predecessor blocks: bb3 bb2
-  $14: phi(bb3: $13, bb2: $12)
+  predecessor blocks: bb2 bb3
+  $14: phi(bb2: $12, bb3: $13)
   Return freeze $14
 ```
 

compiler/forget/src/__tests__/fixtures/hir/mutable-lifetime-loops.expect.md

@@ -97,11 +97,11 @@ bb3:
   [12] Const mutate $29 = Call mutate cond$8(mutate a$21)
   If (read $29) then:bb2 else:bb1
 bb2:
-  predecessor blocks: bb1 bb3
-  a$30: phi(bb1: a$18, bb3: a$21)
-  b$31: phi(bb1: b$20, bb3: b$23)
-  c$32: phi(bb1: c$22, bb3: c$25)
-  d$33[-1:14]: phi(bb1: d$24, bb3: d$26)
+  predecessor blocks: bb3 bb1
+  a$30: phi(bb3: a$21, bb1: a$18)
+  b$31: phi(bb3: b$23, bb1: b$20)
+  c$32: phi(bb3: c$25, bb1: c$22)
+  d$33[-1:14]: phi(bb3: d$26, bb1: d$24)
   If (read a$30) then:bb7 else:bb7
 bb7:
   predecessor blocks: bb2

compiler/forget/src/__tests__/fixtures/hir/mutable-liverange-loop.expect.md

@@ -83,7 +83,7 @@ bb3:
   [7] Const mutate $21 = Call mutate cond$7(mutate a$12)
   If (read $21) then:bb2 else:bb1
 bb2:
-  predecessor blocks: bb1 bb3
+  predecessor blocks: bb3 bb1
   If (read a$12) then:bb7 else:bb7
 bb7:
   predecessor blocks: bb2

compiler/forget/src/__tests__/fixtures/hir/reassignment-conditional.expect.md

@@ -32,8 +32,8 @@ bb2:
   [4] Reassign mutate x$9 = Array []
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
-  x$11: phi(bb0: x$7, bb2: x$9)
+  predecessor blocks: bb2 bb0
+  x$11: phi(bb2: x$9, bb0: x$7)
   [5] Let mutate _$12 = JSX <read Component$0 x={freeze x$11} ></read Component$0>
   [6] Call read y$8.push(read props$6.p2)
   [7] Const mutate $15 = JSX <read Component$0 x={read x$11} y={read y$8} ></read Component$0>

compiler/forget/src/__tests__/fixtures/hir/reverse-postorder.expect.md

@@ -72,8 +72,8 @@ bb13:
   [9] Reassign mutate x$15 = read props$6.c
   Goto bb1
 bb1:
-  predecessor blocks: bb13 bb12 bb8 bb6 bb4
-  x$16: phi(bb13: x$15, bb12: x$14, bb8: x$11, bb6: x$12, bb4: x$13)
+  predecessor blocks: bb8 bb6 bb4 bb12 bb13
+  x$16: phi(bb8: x$11, bb6: x$12, bb4: x$13, bb12: x$14, bb13: x$15)
   [10] read x$16
   Return
 ```

compiler/forget/src/__tests__/fixtures/hir/ssa-call-jsx-2.expect.md

@@ -48,7 +48,7 @@ bb2:
   [6] Let mutate _$15 = JSX <read $14 a={freeze a$11} ></read $14>
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
+  predecessor blocks: bb2 bb0
   [7] Call mutate foo$4(read a$11, mutate b$12)
   [8] Const mutate $19 = "div"
   [9] Const mutate $20 = JSX <read $19 a={freeze a$11} b={freeze b$12} ></read $19>

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

@@ -31,8 +31,8 @@ bb2:
   [5] Reassign mutate x$11 = 3
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
-  x$17: phi(bb0: x$7, bb2: x$11)
+  predecessor blocks: bb2 bb0
+  x$17: phi(bb2: x$11, bb0: x$7)
   [6] Const mutate $12 = 3
   [7] Const mutate $14 = Binary read y$8 === read $12
   If (read $14) then:bb4 else:bb3
@@ -41,8 +41,8 @@ bb4:
   [8] Reassign mutate x$15 = 5
   Goto bb3
 bb3:
-  predecessor blocks: bb1 bb4
-  x$16: phi(bb1: x$17, bb4: x$15)
+  predecessor blocks: bb4 bb1
+  x$16: phi(bb4: x$15, bb1: x$17)
   [9] Reassign mutate y$18 = read x$16
   Return
 ```

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

@@ -28,8 +28,8 @@ bb2:
   [5] Reassign mutate x$9 = 3
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
-  x$10: phi(bb0: x$5, bb2: x$9)
+  predecessor blocks: bb2 bb0
+  x$10: phi(bb2: x$9, bb0: x$5)
   [6] Reassign mutate y$11 = read x$10
   Return
 ```

compiler/forget/src/__tests__/fixtures/hir/ssa-for-of.expect.md

@@ -22,7 +22,7 @@ bb0:
   [1] Let mutate items$5 = Array []
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb3 bb5
+  predecessor blocks: bb0 bb5 bb3
   If (read items$5) then:bb3 else:bb2
 bb3:
   predecessor blocks: bb1

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

@@ -31,7 +31,7 @@ bb3:
   [4] Let mutate z$8 = read x$5
   Goto bb1
 bb1:
-  predecessor blocks: bb3 bb2
+  predecessor blocks: bb2 bb3
   Return
 ```
 

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

@@ -36,9 +36,9 @@ bb3:
   [6] Reassign mutate y$11 = 3
   Goto bb1
 bb1:
-  predecessor blocks: bb3 bb2
-  x$12: phi(bb3: x$6, bb2: x$10)
-  y$13: phi(bb3: y$11, bb2: y$7)
+  predecessor blocks: bb2 bb3
+  x$12: phi(bb2: x$10, bb3: x$6)
+  y$13: phi(bb2: y$7, bb3: y$11)
   [7] Let mutate t$14 = Object { x: read x$12, y: read y$13 }
   Return freeze t$14
 ```

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

@@ -26,8 +26,8 @@ bb2:
   [4] Reassign mutate x$7 = 2
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
-  x$8: phi(bb0: x$4, bb2: x$7)
+  predecessor blocks: bb2 bb0
+  x$8: phi(bb2: x$7, bb0: x$4)
   Return read x$8
 ```
 

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

@@ -33,8 +33,8 @@ bb3:
   [5] Reassign mutate y$9 = 2
   Goto bb1
 bb1:
-  predecessor blocks: bb3 bb2
-  y$10: phi(bb3: y$9, bb2: y$8)
+  predecessor blocks: bb2 bb3
+  y$10: phi(bb2: y$8, bb3: y$9)
   [6] Let mutate x$11 = read y$10
   Return
 ```

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

@@ -25,7 +25,7 @@ bb2:
   [3] Let mutate z$6 = Binary read x$4 + read y$5
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
+  predecessor blocks: bb2 bb0
   Return
 ```
 

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

@@ -25,8 +25,8 @@ bb2:
   [4] Reassign mutate x$7 = 2
   Goto bb1
 bb1:
-  predecessor blocks: bb0 bb2
-  x$8: phi(bb0: x$4, bb2: x$7)
+  predecessor blocks: bb2 bb0
+  x$8: phi(bb2: x$7, bb0: x$4)
   Throw read x$8
 ```