Language: Pre/post increment and decrement (++/--)

[PurHur]

Problem

PreInc, PostInc, PreDec, PostDec are parsed by php-cfg but lib/Compiler.php::compileExpr() throws Unsupported expression (or similar). Loop counters (for ($i = 0; $i < n; $i++)), pagination, and stack depth checks in routers need pre/post semantics.

#300 tracks lint registry mapping until this lands.

Goal

Correct Zend-compatible pre vs post increment/decrement in VM (v1); JIT numeric int paths (v2); AOT follows JIT.

Implementation hints

php-cfg kinds

Probe with bin/print.php -r '++$i; $i++;' — expect Expr_PreInc, Expr_PostInc, etc.

Compiler (lib/Compiler.php)

1. In compileExpr(), branch on increment/decrement nodes.
2. Pre-inc: read old value, add 1, store, value of expression = new value.
3. Post-inc: read old value, add 1, store, value of expression = old value.
4. Lower to existing TYPE_PLUS / assign opcodes or dedicated TYPE_PRE_INC if cleaner for VM.

VM (lib/VM.php)

• If using generic assign+plus, ensure expression result register matches pre/post rules.
• Strings: defer or match Zend coercion policy (document if subset is int-only).

JIT (lib/JIT.php)

• Fast path when operand is typed int in inferred types.
• Fall back to VM call or skip with lint until ready.

Lint

• After Lint: Register ++/-- increment/decrement in UnsupportedRegistry #300, phpc lint should reference this issue until closed.

Tests

• test/compliance/cases/language/pre_post_inc.phpt
• test/compliance/cases/language/pre_post_dec.phpt

Acceptance criteria

docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  php bin/vm.php -r '$i=0; echo ++$i, $i, $i++;'

Prints 112 (Zend: pre-inc returns new, post-inc returns old).

Verification (local / Docker only)

./script/ci-local.sh --filter pre_post_inc

Dependencies

• Language: while, do-while, and for loops (CFG → VM → JIT) #192 for loops (often use ++$i in increment clause)
• Language: break and continue for loops and switch #115 break/continue (orthogonal)
• Lint: Register ++/-- increment/decrement in UnsupportedRegistry #300 lint registry (can land first)

Files

• lib/Compiler.php, lib/VM.php, lib/JIT.php
• lib/Lint/UnsupportedRegistry.php (via Lint: Register ++/-- increment/decrement in UnsupportedRegistry #300)