https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92574
Bug ID: 92574
Summary: Inefficient code for multidimensional array assess
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: hjl.tools at gmail dot com
Target Milestone: ---
For
[hjl@gnu-skx-1 tmp]$ cat foo3.c
extern long bar[25][10];
long
foo (long ip, long itp)
{
long ip1 = ip + 1;
long itp1 = itp + 1;
return (bar[ip][itp]
+ bar[ip][itp1]
+ bar[ip1][itp]
+ bar[ip1][itp1]);
}
On x86-64 GCC -O2 generate:
.type foo, @function
foo:
.LFB0:
.cfi_startproc
leaq (%rdi,%rdi,4), %rax
leaq 1(%rsi), %rcx
addq %rax, %rax
leaq (%rax,%rsi), %rdx
addq %rcx, %rax
movq bar(,%rax,8), %rax
addq bar(,%rdx,8), %rax
leaq 5(%rdi,%rdi,4), %rdx
addq %rdx, %rdx
addq %rdx, %rsi
addq %rcx, %rdx
addq bar(,%rsi,8), %rax
addq bar(,%rdx,8), %rax
ret
.cfi_endproc
Clang 8 generates:
.type foo,@function
foo: # @foo
.cfi_startproc
# %bb.0:
shlq $4, %rdi
leaq (%rdi,%rdi,4), %rcx
movq bar+8(%rcx,%rsi,8), %rax
addq bar(%rcx,%rsi,8), %rax
addq bar+80(%rcx,%rsi,8), %rax
addq bar+88(%rcx,%rsi,8), %rax
retq
.Lfunc_end0:
.size foo, .Lfunc_end0-foo
.cfi_endproc
