re-use `sprintf()` optimisation for `printf()` #19658

realFlowControl · 2025-09-01T11:21:09Z

This PR piggybacks on #14546

test.php:

<?php

$a = 'foo';
$b = 'bar';

ob_start();
for ($i = 0; $i < 100_000_000; $i++) {
    printf("%s-%s", $a, $b);
    ob_clean();
}
ob_end_clean();

See hyperfine run, where php-orig is without this patch:

hyperfine './php-orig -d opcache.enable_cli=1 test.php' './sapi/cli/php -d opcache.enable_cli=1 test.php'
Benchmark 1: ./php-orig -d opcache.enable_cli=1 test.php
  Time (mean ± σ):     10.490 s ±  0.053 s    [User: 10.421 s, System: 0.038 s]
  Range (min … max):   10.443 s … 10.621 s    10 runs
 
Benchmark 2: ./sapi/cli/php -d opcache.enable_cli=1 test.php
  Time (mean ± σ):      8.207 s ±  0.135 s    [User: 8.100 s, System: 0.035 s]
  Range (min … max):    8.077 s …  8.489 s    10 runs

Summary
  ./sapi/cli/php -d opcache.enable_cli=1 test.php ran
    1.28 ± 0.02 times faster than ./php-orig -d opcache.enable_cli=1 test.php

The generated opcodes before optimizer:

./sapi/cli/php -d opcache.enable_cli=1 -d opcache.opt_debug_level=0x10000 test.php     

$_main:
     ; (lines=21, args=0, vars=3, tmps=13)
     ; (before optimizer)
     ; /usr/local/src/php/php-src/test.php:1-12
     ; return  [] RANGE[0..0]
0000 ASSIGN CV0($a) string("foo")
0001 ASSIGN CV1($b) string("bar")
0002 INIT_FCALL 0 80 string("ob_start")
0003 DO_ICALL
0004 ASSIGN CV2($i) int(0)
0005 JMP 0016
0006 T8 = ROPE_INIT 3 CV0($a)
0007 T8 = ROPE_ADD 1 T8 string("-")
0008 T7 = ROPE_END 2 T8 CV1($b)
0009 T10 = COPY_TMP T7
0010 ECHO T7
0011 T11 = STRLEN T10
0012 FREE T11
0013 INIT_FCALL 0 80 string("ob_clean")
0014 DO_ICALL
0015 PRE_INC CV2($i)
0016 T14 = IS_SMALLER CV2($i) int(100000000)
0017 JMPNZ T14 0006
0018 INIT_FCALL 0 80 string("ob_end_clean")
0019 DO_ICALL
0020 RETURN int(1)

... and after optimizer:

./sapi/cli/php -d opcache.enable_cli=1 -d opcache.opt_debug_level=0x20000 test.php

$_main:
     ; (lines=18, args=0, vars=3, tmps=3)
     ; (after optimizer)
     ; /usr/local/src/php/php-src/test.php:1-12
0000 ASSIGN CV0($a) string("foo")
0001 ASSIGN CV1($b) string("bar")
0002 INIT_FCALL 0 80 string("ob_start")
0003 DO_ICALL
0004 ASSIGN CV2($i) int(0)
0005 JMP 0013
0006 T4 = ROPE_INIT 3 CV0($a)
0007 T4 = ROPE_ADD 1 T4 string("-")
0008 T3 = ROPE_END 2 T4 CV1($b)
0009 ECHO T3
0010 INIT_FCALL 0 80 string("ob_clean")
0011 DO_ICALL
0012 PRE_INC CV2($i)
0013 T3 = IS_SMALLER CV2($i) int(100000000)
0014 JMPNZ T3 0006
0015 INIT_FCALL 0 80 string("ob_end_clean")
0016 DO_ICALL
0017 RETURN int(1)

realFlowControl · 2025-09-01T13:48:18Z

There is one failing test now:

========DIFF========
001- Fatal error: Uncaught Error: Undefined constant "A" in %s:%d
002- Stack trace:
003- #0 %s(%d): getA()
004- #1 {main}
005-   thrown in %s on line %d
001+ A=hello
========DONE========
FAIL Bug #66251 (Constants get statically bound at compile time when Optimized) [ext/opcache/tests/bug66251.phpt]

That test got introduced in https://bugs.php.net/bug.php?id=66251 and honestly I am not sure about what that test is actually testing ...

OPcodes for the test before this PR:

$ php -d opcache.enable=1 -d opcache.enable_cli=1 -d opcache.optimization_level=-1 -d opcache.opt_debug_level=0x20000 test_bug66251.php

$_main:
     ; (lines=8, args=0, vars=0, tmps=1)
     ; (after optimizer)
     ; /Users/florian.engelhardt/Work/php-src/test_bug66251.php:1-5
0000 INIT_FCALL 2 112 string("printf")
0001 SEND_VAL string("A=%s
") 1
0002 INIT_FCALL 0 96 string("geta")
0003 V0 = DO_UCALL
0004 SEND_VAR V0 2
0005 DO_ICALL
0006 DECLARE_CONST string("A") string("hello")
0007 RETURN int(1)

getA:
     ; (lines=2, args=0, vars=0, tmps=1)
     ; (after optimizer)
     ; /Users/florian.engelhardt/Work/php-src/test_bug66251.php:4-4
0000 T0 = FETCH_CONSTANT string("A")
0001 RETURN T0

and after:

./sapi/cli/php -d opcache.enable=1 -d opcache.enable_cli=1 -d opcache.optimization_level=-1 -d opcache.opt_debug_level=0x20000 test_bug66251.php

$_main:
     ; (lines=8, args=0, vars=0, tmps=3)
     ; (after optimizer)
     ; /Users/florian.engelhardt/Work/php-src/test_bug66251.php:1-5
0000 INIT_FCALL 0 80 string("geta")
0001 V0 = DO_UCALL
0002 T1 = ROPE_INIT 3 string("A=")
0003 T1 = ROPE_ADD 1 T1 V0
0004 T0 = ROPE_END 2 T1 string("\n")
0005 ECHO T0
0006 DECLARE_CONST string("A") string("hello")
0007 RETURN int(1)
LIVE RANGES:
     0: 0002 - 0003 (tmp/var)
     1: 0002 - 0004 (rope)

getA:
     ; (lines=1, args=0, vars=0, tmps=0)
     ; (after optimizer)
     ; /Users/florian.engelhardt/Work/php-src/test_bug66251.php:4-4
0000 RETURN string("hello")

realFlowControl · 2025-09-01T14:02:11Z

I just see that the sprintf() optimisation triggers the same behaviour (just replace the printf() call with a call to sprintf())

Zend/zend_compile.c

realFlowControl · 2025-09-02T06:46:19Z

@dstogov do you have an idea why the printf() opcode changes trigger the optimisation in the getA() function from:

0000 T0 = FETCH_CONSTANT string("A")

to

0000 RETURN string("hello")

realFlowControl · 2025-09-02T09:54:33Z

This is happening in pass1

php-src/Zend/Optimizer/pass1.c

Lines 149 to 161 in d25687b

    
           if (opline->op2_type == IS_CONST && 
        
           	Z_TYPE(ZEND_OP2_LITERAL(opline)) == IS_STRING) { 
        
           	/* substitute persistent constants */ 
        
           	if (!zend_optimizer_get_persistent_constant(Z_STR(ZEND_OP2_LITERAL(opline)), &result, 1)) { 
        
           		if (!ctx->constants || !zend_optimizer_get_collected_constant(ctx->constants, &ZEND_OP2_LITERAL(opline), &result)) { 
        
           			break; 
        
           		} 
        
           	} 
        
           	if (Z_TYPE(result) == IS_CONSTANT_AST) { 
        
           		break; 
        
           	} 
        
           	replace_by_const_or_qm_assign(op_array, opline, &result); 
        
           }

The problem seems to be that the ROPE optimisation removes the DO_ICALL which resets collect_constants to 0 in pass1.c, I played a bit with it and:

diff --git a/Zend/Optimizer/pass1.c b/Zend/Optimizer/pass1.c
index fe92db583fc..e83a87de5b8 100644
--- a/Zend/Optimizer/pass1.c
+++ b/Zend/Optimizer/pass1.c
@@ -264,6 +264,12 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
                        collect_constants = 0;
                        break;
                }
+               case ZEND_DO_UCALL:
+               case ZEND_DO_FCALL:
+               case ZEND_DO_FCALL_BY_NAME:
+                       collect_constants = 0;
+                       break;
                case ZEND_STRLEN:
                        if (opline->op1_type == IS_CONST &&
                                        zend_optimizer_eval_strlen(&result, &ZEND_OP1_LITERAL(opline)) == SUCCESS) {

solves the issue, although this might have side effects beyond my understanding ..

I've applied this patch in 1526406 and CI is green, yet I fear that this has some consequences CI does not cover 😉

realFlowControl · 2025-09-02T11:23:59Z

So as expected, with 1526406 the behaviour changes for

<?php
echo getA();
const A="hello";
function getA() {return A;}

from:

$ php -d opcache.enable=1 -d opcache.enable_cli=1 -d opcache.optimization_level=-1 -d opcache.opt_debug_level=0x20000 test_bug66251.php

$_main:
     ; (lines=5, args=0, vars=0, tmps=1)
     ; (after optimizer)
     ; /Users/florian.engelhardt/Work/php-src/test_bug66251.php:1-5
0000 INIT_FCALL 0 80 string("geta")
0001 V0 = DO_UCALL
0002 ECHO V0
0003 DECLARE_CONST string("A") string("hello")
0004 RETURN int(1)

getA:
     ; (lines=1, args=0, vars=0, tmps=0)
     ; (after optimizer)
     ; /Users/florian.engelhardt/Work/php-src/test_bug66251.php:4-4
0000 RETURN string("hello")
hello%

to:

./sapi/cli/php -d opcache.enable=1 -d opcache.enable_cli=1 -d opcache.optimization_level=-1 -d opcache.opt_debug_level=0x20000 test_bug66251.php

$_main:
     ; (lines=5, args=0, vars=0, tmps=1)
     ; (after optimizer)
     ; /Users/florian.engelhardt/Work/php-src/test_bug66251.php:1-5
0000 INIT_FCALL 0 96 string("geta")
0001 V0 = DO_UCALL
0002 ECHO V0
0003 DECLARE_CONST string("A") string("hello")
0004 RETURN int(1)

getA:
     ; (lines=2, args=0, vars=0, tmps=1)
     ; (after optimizer)
     ; /Users/florian.engelhardt/Work/php-src/test_bug66251.php:4-4
0000 T0 = FETCH_CONSTANT string("A")
0001 RETURN T0

Fatal error: Uncaught Error: Undefined constant "A" in /Users/florian.engelhardt/Work/php-src/test_bug66251.php:4
Stack trace:
#0 /Users/florian.engelhardt/Work/php-src/test_bug66251.php(2): getA()
#1 {main}
  thrown in /Users/florian.engelhardt/Work/php-src/test_bug66251.php on line 4

Zend/Optimizer/pass1.c

Zend/zend_compile.c

arnaud-lb · 2025-09-02T12:45:19Z

Zend/Optimizer/block_pass.c

+				/* Check for printf optimization from `zend_compile_func_printf()`
+				 * where the result of `printf()` is actually unused and remove the
+				 * superflous COPY_TMP, STRLEN and FREE opcodes:
+				 * T1 = COPY_TMP T0
+				 * ECHO T0
+				 * T2 = STRLEN T1
+				 * FREE T2
+				 */


I believe this is already handled by zend_optimize_cfg():

printf("%s\n", $a);

optimization_level=0:

0000 T2 = ROPE_INIT 3 string("A=") 0001 T2 = ROPE_ADD 1 T2 CV0($s) 0002 T1 = ROPE_END 2 T2 string("\n") 0003 T4 = COPY_TMP T1 0004 ECHO T1 0005 T5 = STRLEN T4 0006 FREE T5 0007 RETURN int(1)

optimization_level=$((1<<4)):

0000 T2 = ROPE_INIT 3 string("A=") 0001 T2 = ROPE_ADD 1 T2 CV0($s) 0002 T1 = ROPE_END 2 T2 string("\n") 0003 ECHO T1 0004 RETURN int(1)

Did you remove my changes when testing this? Cause I can't get this result when I remove my code, also I do believe that these changes in the block_pass.c are part of the optimisation level that you choose (the zend_optimize_cfg() run)

My bad, I did comment out your change before testing this but I think I didn't rebuild after that. So yeah what I observed was the result of your change :)

An alternative would be to support ZEND_COPY_TMP in dce.c:

diff --git a/Zend/Optimizer/dce.c b/Zend/Optimizer/dce.c index a00fd8bc6ad..bdc165de655 100644 --- a/Zend/Optimizer/dce.c +++ b/Zend/Optimizer/dce.c @@ -124,6 +124,7 @@ static inline bool may_have_side_effects( case ZEND_FUNC_NUM_ARGS: case ZEND_FUNC_GET_ARGS: case ZEND_ARRAY_KEY_EXISTS: + case ZEND_COPY_TMP: /* No side effects */ return 0; case ZEND_FREE: @@ -428,7 +429,9 @@ static bool dce_instr(context *ctx, zend_op *opline, zend_ssa_op *ssa_op) { if ((opline->op1_type & (IS_VAR|IS_TMP_VAR))&& !is_var_dead(ctx, ssa_op->op1_use)) { if (!try_remove_var_def(ctx, ssa_op->op1_use, ssa_op->op1_use_chain, opline)) { if (may_be_refcounted(ssa->var_info[ssa_op->op1_use].type) - && opline->opcode != ZEND_CASE && opline->opcode != ZEND_CASE_STRICT) { + && opline->opcode != ZEND_CASE + && opline->opcode != ZEND_CASE_STRICT + && opline->opcode != ZEND_COPY_TMP) { free_var = ssa_op->op1_use; free_var_type = opline->op1_type; }

re-use sprintf() optimisation for printf()

40e2a53

github-actions bot added Category: Engine Category: Optimizer labels Sep 1, 2025

handle special printf() case

353d28f

TimWolla reviewed Sep 1, 2025

View reviewed changes

Zend/zend_compile.c Outdated Show resolved Hide resolved

fix printf(%%) case

121da2e

do not collect constants after any UCALL/FCALL

1526406

realFlowControl marked this pull request as ready for review September 2, 2025 10:44

realFlowControl requested a review from dstogov as a code owner September 2, 2025 10:44

arnaud-lb reviewed Sep 2, 2025

View reviewed changes

realFlowControl added 2 commits September 2, 2025 15:38

do not collect constants after FRAMELESS calls either

3626cc0

code cleanup from pr review

2ae379b

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re-use `sprintf()` optimisation for `printf()` #19658

re-use `sprintf()` optimisation for `printf()` #19658

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re-use sprintf() optimisation for printf() #19658

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re-use sprintf() optimisation for printf() #19658

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re-use `sprintf()` optimisation for `printf()` #19658

re-use `sprintf()` optimisation for `printf()` #19658

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