Hi all, Can gatekeeper help review bug940? Thanks. https://bugs.open64.net/show_bug.cgi?id=940 case: int main() { int inc = 0xFFFF; asm volatile ( "add $1, %0\n\t" : "+Q" (inc) : ); printf("inc=%d\n",inc); } $opencc case.c –O0 ./a.out inc=34 // a random number $gcc case.c –O0 ./a.out inc=65536
Analyze:
the output of .s from open64 is:
# 3 int inc = 0xFFFF;
movl $65535,%edi # [0]
movl %edi,-12(%rbp) # [0] inc
.loc 1 4 0
# 4 asm volatile (
movl -12(%rbp),%eax # [0] inc
add $1, %edx // edx never defined before
movzbl %dl,%eax # [0]
The problem is at function Adjust_one_eight_bit_reg, it will insert a
movzbl op.
The tree before:
[ 4, 0] TN158 :- asm TN158<defopnd> ; volatile side_effects
After:
[ 4, 0] TN160(%rdx) :- asm TN158(%rax) ; volatile side_effects
[ 4, 0] TN158(%rax) :- movzbl TN160(%rdx) ;
For asm volatile (
"add $1, %0\n\t"
: "+Q" (inc)
before insert, TN158 is both input and output of asm. For inline asm if the
input and ouput are the same, we need to make sure they use the same TN,
stored in the same register. So it need to insert another mov from TN158 to
TN160 before asm.
such as:
[ 4, 0] TN160 :- mov TN158 ; copy
[ 4, 0] TN160 :- asm TN160 ; volatile side_effects
[ 4, 0] TN158 :- mov32 TN160 ; copy
Thanks
zhuqing
bug940.patch
Description: Binary data
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