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nikicnikic
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Fix bug #78271
When cleaning nops in the dfa pass, we were always keeping the smart branch inhibiting nop that occurs directly before the jump instruction. However, as we skip unreachable blocks entirely, it may happen that we need to keep a nop that occurs further back, prior to the unreachable blocks. Account for that case now. We should really do something about the smart branch situation, this is very fragile...
1 parent 3fa9f9c commit e7a83ec

3 files changed

Lines changed: 59 additions & 10 deletions

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‎NEWS‎

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Original file line numberDiff line numberDiff line change
@@ -24,6 +24,7 @@ PHP NEWS
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. Fixed bug #78189 (file cache strips last character of uname hash). (cmb)
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. Fixed bug #78202 (Opcache stats for cache hits are capped at 32bit NUM).
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(cmb)
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. Fixed bug #78271 (Invalid result of if-else). (Nikita)
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- PCRE:
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. Fixed bug #78197 (PCRE2 version check in configure fails for "##.##-xxx"

‎Zend/tests/bug78271.phpt‎

Lines changed: 27 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,27 @@
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--TEST--
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Bug #78271: Invalid result of if-else
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--FILE--
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<?
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function test($a, $b){
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if ($a==10) {
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$w="x";
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} else {
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$w="y";
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}
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if ($b) {
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$d1="none";
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$d2="block";
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} else {
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$d1="block";
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$d2="none";
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}
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echo $d2.$b."\n";
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}
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test(1, 1);
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?>
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--EXPECT--
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block1

‎ext/opcache/Optimizer/dfa_pass.c‎

Lines changed: 31 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -125,10 +125,37 @@ int zend_dfa_analyze_op_array(zend_op_array *op_array, zend_optimizer_ctx *ctx,
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return SUCCESS;
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}
127127

128+
static zend_bool is_smart_branch_inhibiting_nop(
129+
zend_op_array *op_array, uint32_t target, uint32_t current,
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zend_basic_block *b, zend_basic_block *blocks_end)
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{
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uint32_t next;
133+
/* Target points one past the last non-nop instruction. Make sure there is one. */
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if (target == 0) {
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return 0;
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}
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/* Find the next instruction, skipping unreachable or empty blocks. */
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next = current + 1;
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if (next >= b->start + b->len) {
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do {
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b++;
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if (b == blocks_end) {
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return 0;
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}
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} while (!(b->flags & ZEND_BB_REACHABLE) || b->len == 0);
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next = b->start;
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}
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return (op_array->opcodes[next].opcode == ZEND_JMPZ ||
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op_array->opcodes[next].opcode == ZEND_JMPNZ) &&
152+
zend_is_smart_branch(op_array->opcodes + target - 1);
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}
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128155
static void zend_ssa_remove_nops(zend_op_array *op_array, zend_ssa *ssa, zend_optimizer_ctx *ctx)
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{
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zend_basic_block *blocks = ssa->cfg.blocks;
131-
zend_basic_block *end = blocks + ssa->cfg.blocks_count;
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zend_basic_block *blocks_end = blocks + ssa->cfg.blocks_count;
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zend_basic_block *b;
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zend_func_info *func_info;
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int j;
@@ -152,7 +179,7 @@ static void zend_ssa_remove_nops(zend_op_array *op_array, zend_ssa *ssa, zend_op
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}
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}
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155-
for (b = blocks; b < end; b++) {
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for (b = blocks; b < blocks_end; b++) {
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if (b->flags & (ZEND_BB_REACHABLE|ZEND_BB_UNREACHABLE_FREE)) {
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uint32_t end;
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@@ -174,13 +201,7 @@ static void zend_ssa_remove_nops(zend_op_array *op_array, zend_ssa *ssa, zend_op
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while (i < end) {
175202
shiftlist[i] = i - target;
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if (EXPECTED(op_array->opcodes[i].opcode != ZEND_NOP) ||
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/* Keep NOP to support ZEND_VM_SMART_BRANCH. Using "target-1" instead of
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* "i-1" here to check the last non-NOP instruction. */
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(target > 0 &&
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i + 1 < op_array->last &&
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(op_array->opcodes[i+1].opcode == ZEND_JMPZ ||
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op_array->opcodes[i+1].opcode == ZEND_JMPNZ) &&
183-
zend_is_smart_branch(op_array->opcodes + target - 1))) {
204+
is_smart_branch_inhibiting_nop(op_array, target, i, b, blocks_end)) {
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if (i != target) {
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op_array->opcodes[target] = op_array->opcodes[i];
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ssa->ops[target] = ssa->ops[i];
@@ -240,7 +261,7 @@ static void zend_ssa_remove_nops(zend_op_array *op_array, zend_ssa *ssa, zend_op
240261
}
241262

242263
/* update branch targets */
243-
for (b = blocks; b < end; b++) {
264+
for (b = blocks; b < blocks_end; b++) {
244265
if ((b->flags & ZEND_BB_REACHABLE) && b->len != 0) {
245266
zend_op *opline = op_array->opcodes + b->start + b->len - 1;
246267
zend_optimizer_shift_jump(op_array, opline, shiftlist);

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