perf(minifier): evaluate ternary branches once in minimize_conditional_expression (#23479)

## What & why

`minimize_conditional_expression` ran two folds — the boolean fold (`a ?
true : false` → `!!a`) and
the number fold (`a ? 1 : 0` → `+a`) — and **each** independently called
`expr.consequent.evaluate_value(ctx)` and
`expr.alternate.evaluate_value(ctx)`. So every ternary
evaluated each branch **twice** (4 `evaluate_value` calls per
`ConditionalExpression`).

`evaluate_value` is a recursive constant-evaluation walk over the
operand subtree. This hoists the two
results and reuses them across both folds (4 → 2 calls per ternary).
`minimize_conditional_expression`
runs in `exit_expression` on every `ConditionalExpression`, across the
fixed-point peephole loop, and
ternaries are common — so this is a hot path.

```rust
let consequent_value = expr.consequent.evaluate_value(ctx);
let alternate_value  = expr.alternate.evaluate_value(ctx);
// boolean fold reads the cached values clone-free (as_ref + variant match == into_boolean)
// number  fold consumes them (into_number) — last use
```

The boolean fold reads the cached values **clone-free** (an `as_ref()` +
`Boolean` variant match,
identical to `into_boolean`); the number fold consumes them. Nothing
mutates the operands between the
two folds (the boolean fold only mutates inside arms that `return`), so
the cached values are valid.

## Allocations (measured)

`cargo allocs` shows a small system-allocation reduction, no
regressions:

| file | sys allocs: before → after |
| --- | --- |
| checker.ts | 166 → 162 (**−4**) |
| pdf.mjs | 2614 → 2613 (**−1**) |

(Arena allocs unchanged.) The primary effect is the halved
`evaluate_value` work (instruction count) —
CodSpeed will arbitrate that on this PR. The change is structured to
never do more work than before.

## Behavior-preserving

`cargo test -p oxc_minifier` (535 tests) passes; no snapshot drift
beyond the allocation snapshot above.

---
Prepared with AI assistance.

---------

Co-authored-by: Cameron Clark <cameron.clark@hey.com>

crates/oxc_minifier/src/peephole/minimize_conditional_expression.rs

@@ -377,16 +377,25 @@ impl<'a> PeepholeOptimizations {
             }
         }
 
+        let consequent_value = expr.consequent.evaluate_value(ctx);
+        let alternate_value = expr.alternate.evaluate_value(ctx);
+
         // "a ? true : false" => "!!a"
         // "a ? false : true" => "!a"
         match (
-            expr.consequent
-                .evaluate_value(ctx)
-                .and_then(ConstantValue::into_boolean)
+            consequent_value
+                .as_ref()
+                .and_then(|v| match v {
+                    ConstantValue::Boolean(b) => Some(*b),
+                    _ => None,
+                })
                 .filter(|_| !expr.consequent.may_have_side_effects(ctx)),
-            expr.alternate
-                .evaluate_value(ctx)
-                .and_then(ConstantValue::into_boolean)
+            alternate_value
+                .as_ref()
+                .and_then(|v| match v {
+                    ConstantValue::Boolean(b) => Some(*b),
+                    _ => None,
+                })
                 .filter(|_| !expr.alternate.may_have_side_effects(ctx)),
         ) {
             (Some(true), Some(false)) => {
@@ -406,12 +415,10 @@ impl<'a> PeepholeOptimizations {
         // "a ? 1 : 0" => "+a" (if a is boolean) or "+!!a" (if no parens needed)
         // "a ? 0 : 1" => "+!a" (if no parens needed)
         match (
-            expr.consequent
-                .evaluate_value(ctx)
+            consequent_value
                 .and_then(ConstantValue::into_number)
                 .filter(|_| !expr.consequent.may_have_side_effects(ctx)),
-            expr.alternate
-                .evaluate_value(ctx)
+            alternate_value
                 .and_then(ConstantValue::into_number)
                 .filter(|_| !expr.alternate.may_have_side_effects(ctx)),
         ) {

tasks/track_memory_allocations/allocs_minifier.snap

@@ -1,12 +1,12 @@
 File                       | File size      || Sys allocs     | Sys reallocs   || Arena allocs   | Arena reallocs 
 ---------------------------------------------------------------------------------------------------------------------------
-checker.ts                 | 2.92 MB        ||            166 |             52 ||         152742 |          28244
+checker.ts                 | 2.92 MB        ||            162 |             52 ||         152742 |          28244
 
 App.tsx                    | 415.34 kB      ||            115 |             49 ||          17012 |           2702
 
 RadixUIAdoptionSection.jsx | 2.52 kB        ||             24 |             20 ||             32 |              6
 
-pdf.mjs                    | 567.30 kB      ||           2614 |            249 ||          47485 |           7740
+pdf.mjs                    | 567.30 kB      ||           2613 |            249 ||          47485 |           7740
 
 antd.js                    | 6.69 MB        ||           3084 |            106 ||         337233 |          69333