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Support LONG MUL with overflow detection

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Overflow detection for LONG MUL is added in this patch. Quite different
from 'subs' and 'adds' where overflow can be easily checked via the V
flags, LONG MUL wouldn't set the flags.

We use 'smulh' instruction to get the upper 64 bits of the 128-bit
result and check the top 65 bits to tell whether integer overflow
occurs. [1]

Note that LONG MUL can be substituted by 'adds' or 'lsl' in some cases.
Hence, flag 'use_mul' is introduced in order to select the proper
overflow check check instruction afterwards.

[1]
https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/detecting-overflow-from-mul

Change-Id: I67e8287e9044c2a96b188d4bf6674736713abfe9
This commit is contained in:
Hao Sun 2021-04-21 13:44:35 +00:00 committed by Dmitry Stogov
parent 0482102b04
commit cb52d2731c
1 changed files with 37 additions and 8 deletions
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45
ext/opcache/jit/zend_jit_arm64.dasc
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@ -3179,6 +3179,7 @@ static int zend_jit_math_long_long(dasm_State **Dst,
bool same_ops = zend_jit_same_addr(op1_addr, op2_addr);
zend_reg result_reg;
zend_reg tmp_reg = ZREG_REG0;
bool use_mul = 0;
if (Z_MODE(res_addr) == IS_REG && (res_info & MAY_BE_LONG)) {
if (may_overflow && (res_info & MAY_BE_GUARD)
@ -3258,10 +3259,22 @@ static int zend_jit_math_long_long(dasm_State **Dst,
| NIY // TODO: test
#endif
} else if (opcode == ZEND_MUL) {
| GET_ZVAL_LVAL result_reg, op1_addr, TMP1
| GET_ZVAL_LVAL ZREG_TMP2, op2_addr, TMP2
| mul Rx(result_reg), Rx(result_reg), TMP2
| // TODO: overflow detection
use_mul = 1;
| GET_ZVAL_LVAL ZREG_TMP2, op1_addr, TMP1
| GET_ZVAL_LVAL ZREG_TMP3, op2_addr, TMP1
| mul Rx(result_reg), TMP2, TMP3
if(may_overflow) {
/* Use 'smulh' to get the upper 64 bits fo the 128-bit result.
* For signed multiplication, the top 65 bits of the result will contain
* either all zeros or all ones if no overflow occurred.
* Note that 'cmp, TMP1, Rx(result_reg), asr, #63' is not supported by DynASM/arm64
* currently, and we put 'asr' and 'cmp' separately.
* Flag: bne -> overflow. beq -> no overflow.
*/
| smulh TMP1, TMP2, TMP3
| asr TMP2, Rx(result_reg), #63
| cmp TMP1, TMP2
}
} else {
| GET_ZVAL_LVAL result_reg, op1_addr, TMP1
if ((opcode == ZEND_ADD || opcode == ZEND_SUB)
@ -3280,7 +3293,11 @@ static int zend_jit_math_long_long(dasm_State **Dst,
int32_t exit_point = zend_jit_trace_get_exit_point(opline, 0);
const void *exit_addr = zend_jit_trace_get_exit_addr(exit_point);
if ((res_info & MAY_BE_ANY) == MAY_BE_LONG) {
| bvs >3
if (use_mul) {
| bne >3
} else {
| bvs >3
}
|.cold_code
|3:
| EXT_JMP exit_addr, TMP1
@ -3289,7 +3306,11 @@ static int zend_jit_math_long_long(dasm_State **Dst,
| mov Rx(Z_REG(res_addr)), Rx(result_reg)
}
} else if ((res_info & MAY_BE_ANY) == MAY_BE_DOUBLE) {
| bvc >3
if (use_mul) {
| beq >3
} else {
| bvc >3
}
|.cold_code
|3:
| EXT_JMP exit_addr, TMP1
@ -3299,9 +3320,17 @@ static int zend_jit_math_long_long(dasm_State **Dst,
}
} else {
if (res_info & MAY_BE_LONG) {
| bvs >1
if (use_mul) {
| bne >1
} else {
| bvs >1
}
} else {
| bvc >1
if (use_mul) {
| beq >1
} else {
| bvc >1
}
}
}
}