https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71275
Bug ID: 71275
Summary: [7 regression] Performance drop after r235660 on
x86-64 in 32-bit mode.
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: ysrumyan at gmail dot com
Target Milestone: ---
Regression can be seen at attached test-case. In the tail block of innermost
loop redundant fill was added:
before r235660 r235660
.L3:
addl $1, %esi addl $1, %esi
addl %eax, %ebx addl %eax, %ebx
movw %bp, (%edi,%ecx) movl 44(%esp), %edx
movswl %si, %ebp movswl %si, %eax
cmpl (%esp), %ebp cmpl %edi, %eax
jl .L6 movw %bp, (%edx,%ecx)
jl .L6
In result we got up to 14% slow-down on one important benchmark.
It is clear that it is not profitable to keep value of loop upper bound on
register instead of the address base.
