https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78343
Bug ID: 78343
Summary: Loop is not eliminated
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: krister.walfridsson at gmail dot com
Target Milestone: ---
GCC 6 and trunk generates inefficient code for the loop
unsigned int test(unsigned int quant)
{
unsigned int sum = 0;
for (unsigned int i = 0; i < quant; ++i){
sum += quant;
}
return sum;
}
as noted in the tweet
https://twitter.com/lefticus/status/797593368037642244?s=09.
This is a regression introduced in r233207; GCC used to generate
test:
movl %edi, %eax
imull %edi, %eax
ret
before r233207, and it generates a meaningless loop
test:
testl %edi, %edi
je .L4
xorl %edx, %edx
.L3:
addl $1, %edx
cmpl %edx, %edi
jne .L3
movl %edi, %eax
imull %edi, %eax
ret
.L4:
xorl %eax, %eax
ret
after that change.
