------- Comment #2 from jv244 at cam dot ac dot uk 2008-11-19 13:18 -------
(In reply to comment #1)
> Do you know of any compilers that catch this? As you say, it is not so easy
> to
> fix.
I believe ifort gets this right (compiled with 'ifort -S -heap-arrays 64), but
this is just looking at the assembly, which normally contains calls to
for_allocate if a temp is generated:
s1_:
# parameter 1: %rdi
..B1.1: # Preds ..B1.0
..___tag_value_s1_.1: #1.12
movq 48(%rdi), %rsi #4.1
movl $1, %r8d #4.1
testq %rsi, %rsi #4.1
jle ..B1.5 # Prob 10% #4.1
# LOE rbx rbp rsi rdi r8 r12 r13 r14 r15
..B1.2: # Preds ..B1.1
movq (%rdi), %rax #4.1
movq 56(%rdi), %rcx #4.1
movq %rcx, %rdx #4.1
subq %rcx, %rax #
# LOE rax rdx rcx rbx rbp rsi r8 r12 r13 r14
r15
..B1.3: # Preds ..B1.3 ..B1.2
movl %r8d, (%rdx,%rax) #4.1
addq %rcx, %rdx #4.1
addq $1, %r8 #4.1
cmpq %rsi, %r8 #4.1
jle ..B1.3 # Prob 82% #4.1
# LOE rax rdx rcx rbx rbp rsi r8 r12 r13 r14
r15
..B1.5: # Preds ..B1.3 ..B1.1
ret #5.1
.align 2,0x90
>
> BTW you say that this another case where an unneeded temp is created. I can
> see your PRs after this. Which ones come before?
I've added a number of these as blocking PR36854. As mentioned before, all
derived from CP2K. I believe these are relatively important to fix, the
performance inpact of generating an unneeded temp can be very large.
Joost
>
> Paul
>
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38111
