On 10.09.2010, at 16:08, Mai, Haohui wrote:
> Hi,
>
> I'm using LLVM 2.7 right now, and I found "opt
-std-compile-opts" has
> missed some opportunities for optimization:
>
> define void @spa.main() readonly {
> entry:
> %tmp = load i32* @dst-ip ; <i32> [#uses=3]
> %tmp1 = and i32 %tmp, -16777216 ; <i32> [#uses=1]
> %tmp2 = icmp eq i32 %tmp1, 167772160 ; <i1> [#uses=2]
> %tmp3 = and i32 %tmp, -65536 ; <i32> [#uses=2]
> %tmp4 = icmp ne i32 %tmp3, 168296448 ; <i1> [#uses=1]
> %tmp5 = and i1 %tmp2, %tmp4 ; <i1> [#uses=1]
> %tmp6 = and i32 %tmp, -256 ; <i32> [#uses=2]
> %tmp7 = icmp eq i32 %tmp6, 168296704 ; <i1> [#uses=1]
> %tmp8 = icmp eq i32 %tmp3, 168296448 ; <i1> [#uses=2]
> %tmp9 = icmp ne i32 %tmp6, 168296704 ; <i1> [#uses=1]
> %tmp10 = and i1 %tmp8, %tmp9 ; <i1> [#uses=1]
> %tmp11 = load i32* @src-ip ; <i32> [#uses=1]
> %tmp12 = and i32 %tmp11, -16777216 ; <i32> [#uses=1]
> %tmp13 = icmp eq i32 %tmp12, 721420288 ; <i1> [#uses=3]
> %tmp14 = and i1 %tmp2, %tmp5 ; <i1> [#uses=1]
> %tmp15 = and i1 %tmp13, %tmp14 ; <i1> [#uses=1]
> tail call void @spa.assert(i1 %tmp15)
> %tmp16 = and i1 %tmp8, %tmp10 ; <i1> [#uses=1]
> %tmp17 = and i1 %tmp13, %tmp16 ; <i1> [#uses=1]
> tail call void @spa.assert(i1 %tmp17)
> %tmp18 = and i1 %tmp13, %tmp7 ; <i1> [#uses=1]
> tail call void @spa.assert(i1 %tmp18)
> ret void
> }
>
> Please notice the following code sequences are not optimal:
>
> %tmp5 = and i1 %tmp2, %tmp4 ; <i1> [#uses=1]
> %tmp14 = and i1 %tmp2, %tmp5 ; <i1> [#uses=1]
>
> Is it a problem of scalar evolution or I just need to call another pass?
The reassociate pass used to do this but it was disabled for "i1"
values because
it pessimized some code (r95333). I pushed a fix (r113651) to trunk which adds
support
for this optimization to the InstructionSimplify analysis (which is run, among
others,
by the Instcombine pass).
Thanks for bringing this up. :)