[PATCH] D57779: [SLP] Add support for throttling.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added a comment.

In D57779#2743946 <https://reviews.llvm.org/D57779#2743946>, @dtemirbulatov wrote:

>> Why do we need MinVecNodes? MinTreeSize  and all associated analysis must be enough
>
> it is Transforms/SLPVectorizer/X86/tiny-tree.ll transform that scared me. 
> From:
> define void @tiny_tree_not_fully_vectorizable(double* noalias nocapture %dst, double* noalias nocapture readonly %src, i64 %count) #0 { 
> entry:
>
>   %cmp12 = icmp eq i64 %count, 0
>   br i1 %cmp12, label %for.end, label %for.body
>
> for.body:                                         ; preds = %entry, %for.body
>
>   %i.015 = phi i64 [ %inc, %for.body ], [ 0, %entry ]
>   %dst.addr.014 = phi double* [ %add.ptr4, %for.body ], [ %dst, %entry ]
>   %src.addr.013 = phi double* [ %add.ptr, %for.body ], [ %src, %entry ]
>   %0 = load double, double* %src.addr.013, align 8
>   store double %0, double* %dst.addr.014, align 8
>   %arrayidx2 = getelementptr inbounds double, double* %src.addr.013, i64 2
>   %1 = load double, double* %arrayidx2, align 8
>   %arrayidx3 = getelementptr inbounds double, double* %dst.addr.014, i64 1
>   store double %1, double* %arrayidx3, align 8
>   %add.ptr = getelementptr inbounds double, double* %src.addr.013, i64 %i.015
>   %add.ptr4 = getelementptr inbounds double, double* %dst.addr.014, i64 %i.015
>   %inc = add i64 %i.015, 1
>   %exitcond = icmp eq i64 %inc, %count
>   br i1 %exitcond, label %for.end, label %for.body
>
> for.end:                                          ; preds = %for.body, %entry
>
>   ret void
>
> }
> to:
> define void @tiny_tree_not_fully_vectorizable(double* noalias nocapture %dst, double* noalias nocapture readonly %src, i64 %count) #0 {
> entry:
>
>   %cmp12 = icmp eq i64 %count, 0
>   br i1 %cmp12, label %for.end, label %for.body
>
> for.body:                                         ; preds = %for.body, %entry
>
>   %i.015 = phi i64 [ %inc, %for.body ], [ 0, %entry ]
>   %dst.addr.014 = phi double* [ %add.ptr4, %for.body ], [ %dst, %entry ]
>   %src.addr.013 = phi double* [ %add.ptr, %for.body ], [ %src, %entry ]
>   %0 = load double, double* %src.addr.013, align 8
>   %arrayidx2 = getelementptr inbounds double, double* %src.addr.013, i64 2
>   %1 = load double, double* %arrayidx2, align 8
>   %arrayidx3 = getelementptr inbounds double, double* %dst.addr.014, i64 1
>   %2 = insertelement <2 x double> poison, double %0, i32 0
>   %3 = insertelement <2 x double> %2, double %1, i32 1
>   %4 = bitcast double* %dst.addr.014 to <2 x double>*
>   store <2 x double> %3, <2 x double>* %4, align 8
>   %add.ptr = getelementptr inbounds double, double* %src.addr.013, i64 %i.015
>   %add.ptr4 = getelementptr inbounds double, double* %dst.addr.014, i64 %i.015
>   %inc = add i64 %i.015, 1
>   %exitcond = icmp eq i64 %inc, %count
>   br i1 %exitcond, label %for.end, label %for.body
>
> for.end:                                          ; preds = %for.body, %entry
>
>   ret void
>
> }
>
> but now with llvm-mca with -mattr=+corei7-avx, I see the change from 1111 to 1014 cycles, so it looks good. I will check other cases.

If so, it just means that oir min-tree-size analysis os too strict and must be fixed in general, buy by introducing  some new throttling-specific options. We may have the same situation without throttling.


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  https://reviews.llvm.org/D57779/new/

https://reviews.llvm.org/D57779