[llvm-dev] sinking in LICM

[Quentin Colombet via llvm-dev]

Hi,

That sounds like a job for the SinkingPass. Doesn’t it catch this case?

Cheers,
-Quentin
> On Aug 10, 2017, at 11:34 AM, via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi,
> 
> In the IR below, %tmp.7 and %tmp.8 are not used in loop, so we can sink them in exit blocks. However, LICM do not handle this case because of the check in isNotUsedInLoop() which returns false when a PHI node use is hooked from a block inside the loop. I'm not sure if we really need to have this check even when the PHI is outside the loop?
> 
> define i32 @test7(i32 %N, i32 %N2, i1 %C) {
> Entry:
>        br label %Loop
> Loop:
>        %N_addr.0.pn = phi i32 [ %dec, %ContLoop ], [ %N, %Entry ]
>        %tmp.6 = mul i32 %N, %N_addr.0.pn
>        %tmp.7 = sub i32 %tmp.6, %N
>        %tmp.8 = sub i32 %tmp.6, %N2
>        %dec = add i32 %N_addr.0.pn, -1
>        br i1 %C, label %ContLoop, label %Out12
> 
> ContLoop:
>        %tmp.1 = icmp ne i32 %N_addr.0.pn, 1
>        br i1 %tmp.1, label %Loop, label %Out12
> 
> Out12:
>  %tmp.7.8.lcssa1 = phi i32 [%tmp.8, %ContLoop], [%tmp.7, %Loop]
>  ret i32 %tmp.7.8.lcssa1
> }
> 
> Is there any problem I'm missing if we convert the above IR to the IR below :
> 
> define i32 @test7(i32 %N, i32 %N2, i1 %C) {
> Entry:
>  br label %Loop
> 
> Loop:
>  %N_addr.0.pn = phi i32 [ %dec, %ContLoop ], [ %N, %Entry ]
>  %dec = add i32 %N_addr.0.pn, -1
>  br i1 %C, label %ContLoop, label %Out01
> 
> ContLoop:
>  %tmp.1 = icmp ne i32 %N_addr.0.pn, 1
>  br i1 %tmp.1, label %Loop, label %Out02
> 
> Out01:
>  %N_addr.0.pn.lcssa2 = phi i32 [ %N_addr.0.pn, %Loop ]
>  %tmp.6.le1 = mul i32 %N, %N_addr.0.pn.lcssa2
>  %tmp.8.new = sub i32 %tmp.6.le1, %N2
>  br label %Out12
> 
> Out02:
>  %N_addr.0.pn.lcssa = phi i32 [ %N_addr.0.pn, %ContLoop ]
>  %tmp.6.le = mul i32 %N, %N_addr.0.pn.lcssa
>  %tmp.7.new = sub i32 %tmp.6.le, %N
>  br label %Out12
> 
> Out12:
>  %tmp.7.8.ret = phi i32 [ %tmp.8.new, %Out01 ], [ %tmp.7.new, %Out02 ]
>  ret i32 %tmp.7.8.ret
> }
> 
> Thanks,
> Jun
> 
> 
> -- 
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