#2253: Native code generator could do better
---------------------------------+------------------------------------------
Reporter: dons | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 7.6.1
Component: Compiler (NCG) | Version: 6.8.2
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: Runtime performance bug
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Changes (by simonmar):
* blockedby: 4258 =>
Comment:
I came to check these with the new backend, and it turns out that the old
backend is doing just fine on these now. It might be mostly due to this:
3d8ab554ced45c51f39951f29cc53277d5788c37.
These are compiled with HEAD as of yesterday, with -O2.
Program 1:
{{{
Main_mainzuzdszdwfoldlMzqzuloop_info:
.Lc2vG:
cmpq $100000000,%rsi
jle .Lc2vM
movq %r14,%rbx
jmp *0(%rbp)
.Lc2vM:
cmpq $100000001,%rdi
jle .Lc2vO
movq %r14,%rbx
jmp *0(%rbp)
.Lc2vO:
cmpq $100000008,%r8
jle .Lc2vR
movq %r14,%rbx
jmp *0(%rbp)
.Lc2vR:
movq %rdi,%rbx
imulq %r8,%rbx
movq %rsi,%rax
imulq %rbx,%rax
addq %rax,%r14
incq %rsi
incq %rdi
incq %r8
jmp Main_mainzuzdszdwfoldlMzqzuloop_info
}}}
The new code generator does a bit better, commoning up the duplicate
blocks:
{{{
Main_mainzuzdszdwfoldlMzqzuloop_info:
.Lc2vW:
cmpq $100000000,%rsi
jle .Lc2wt
.Lc2wj:
movq %r14,%rbx
jmp *(%rbp)
.Lc2wt:
cmpq $100000001,%rdi
jg .Lc2wj
cmpq $100000008,%r8
jg .Lc2wj
movq %rdi,%rbx
imulq %r8,%rbx
movq %rsi,%rax
imulq %rbx,%rax
addq %rax,%r14
incq %rsi
incq %rdi
incq %r8
jmp Main_mainzuzdszdwfoldlMzqzuloop_info
}}}
Program 2 (with `-O2 -fno-regs-graph`, the graph-colouring allocator
generates a tiny bit worse code on this one):
{{{
Main_mainzuzdszdwfoldlMzqzuloop_info:
.Lc2mJ:
testq %rsi,%rsi
jle .Lc2mR
.Lc2mS:
addq $4,%r14
decq %rsi
jmp Main_mainzuzdszdwfoldlMzqzuloop_info
.Lc2mR:
movl $1000000000,%esi
jmp r2kR_info
r2kR_info:
.Lc2m8:
testq %rsi,%rsi
jle .Lc2mg
.Lc2mh:
addq $28,%r14
decq %rsi
jmp r2kR_info
.Lc2mg:
movq %r14,%rbx
jmp *(%rbp)
}}}
Program 3:
{{{
Main_mainzuzdszdwfoldlMzqzuloop_info:
.Lc2hW:
testq %rsi,%rsi
jle .Lc2i1
addq $8,%r14
decq %rsi
jmp Main_mainzuzdszdwfoldlMzqzuloop_info
.Lc2i1:
movq %r14,%rbx
jmp *0(%rbp)
}}}
Program 4:
{{{
Main_mainzuzdszdwfoldlMzqzuloop_info:
.Lc2lj:
testq %rsi,%rsi
jle .Lc2lo
addq $36,%r14
decq %rsi
jmp Main_mainzuzdszdwfoldlMzqzuloop_info
.Lc2lo:
movq %r14,%rbx
jmp *0(%rbp)
}}}
Program 5:
{{{
Main_mainzuzdszdwfoldlMzqzuloop_info:
.Lc2rk:
cmpq $100000000,%rsi
jle .Lc2ro
movq %r14,%rbx
jmp *0(%rbp)
.Lc2ro:
cmpq $100000001,%rdi
jle .Lc2rr
movq %r14,%rbx
jmp *0(%rbp)
.Lc2rr:
addq %rsi,%r14
incq %rsi
incq %rdi
jmp Main_mainzuzdszdwfoldlMzqzuloop_info
}}}
Program 6:
{{{
Main_mainzuzdszdwfoldlMzqzuloop_info:
.Lc2tu:
testq %r14,%r14
jle .Lc2tA
cmpq $39999999,%rsi
jle .Lc2tD
jmp *0(%rbp)
.Lc2tA:
jmp *0(%rbp)
.Lc2tD:
cvtsi2sdq %rsi,%xmm0
movsd .Ln2tF(%rip),%xmm1
mulsd %xmm0,%xmm1
addsd %xmm1,%xmm5
decq %r14
incq %rsi
jmp Main_mainzuzdszdwfoldlMzqzuloop_info
}}}
We still need the strength reduction, I'll make a separate ticket for
that.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2253#comment:16>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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