RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2024-11-22 02:33:06 +01:00
Code Issues Projects Releases Wiki Activity

[LoopVectorize] Don't interleave scalar ordered reductions for inner loops

Browse Source 
Consider the following loop:

  void foo(float *dst, float *src, int N) {
    for (int i = 0; i < N; i++) {
      dst[i] = 0.0;
      for (int j = 0; j < N; j++) {
        dst[i] += src[(i * N) + j];
      }
    }
  }

When we are not building with -Ofast we may attempt to vectorise the
inner loop using ordered reductions instead. In addition we also try
to select an appropriate interleave count for the inner loop. However,
when choosing a VF=1 the inner loop will be scalar and there is existing
code in selectInterleaveCount that limits the interleave count to 2
for reductions due to concerns about increasing the critical path.
For ordered reductions this problem is even worse due to the additional
data dependency, and so I've added code to simply disable interleaving
for scalar ordered reductions for now.

Test added here:

  Transforms/LoopVectorize/AArch64/strict-fadd-vf1.ll

Differential Revision: https://reviews.llvm.org/D106646
This commit is contained in:
David Sherwood 2021-07-23 10:52:53 +01:00
parent 3ad8a0b712
commit cdd50ed2ff
2 changed files with 56 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
lib/Transforms/Vectorize/LoopVectorize.cpp
View File

@ -6473,9 +6473,21 @@ unsigned LoopVectorizationCostModel::selectInterleaveCount(ElementCount VF,
// If we have a scalar reduction (vector reductions are already dealt with
// by this point), we can increase the critical path length if the loop
// we're interleaving is inside another loop. Limit, by default to 2, so the
// critical path only gets increased by one reduction operation.
// we're interleaving is inside another loop. For tree-wise reductions
// set the limit to 2, and for ordered reductions it's best to disable
// interleaving entirely.
if (HasReductions && TheLoop->getLoopDepth() > 1) {
bool HasOrderedReductions =
any_of(Legal->getReductionVars(), [&](auto &Reduction) -> bool {
const RecurrenceDescriptor &RdxDesc = Reduction.second;
return RdxDesc.isOrdered();
});
if (HasOrderedReductions) {
LLVM_DEBUG(
dbgs() << "LV: Not interleaving scalar ordered reductions.\n");
return 1;
}
unsigned F = static_cast<unsigned>(MaxNestedScalarReductionIC);
SmallIC = std::min(SmallIC, F);
StoresIC = std::min(StoresIC, F);

42
test/Transforms/LoopVectorize/AArch64/strict-fadd-vf1.ll Normal file
View File

@ -0,0 +1,42 @@
; REQUIRES: asserts
; RUN: opt -loop-vectorize -enable-strict-reductions=true -force-vector-width=1 -S < %s -debug 2>log | FileCheck %s
; RUN: cat log | FileCheck %s --check-prefix=CHECK-DEBUG
target triple = "aarch64-unknown-linux-gnu"
; CHECK-DEBUG: LV: Not interleaving scalar ordered reductions.
define void @foo(float* noalias nocapture %dst, float* noalias nocapture readonly %src, i64 %M, i64 %N) {
; CHECK-LABEL: @foo(
; CHECK-NOT: vector.body
entry:
br label %for.body.us
for.body.us: ; preds = %entry, %for.cond3
%i.023.us = phi i64 [ %inc8.us, %for.cond3 ], [ 0, %entry ]
%arrayidx.us = getelementptr inbounds float, float* %dst, i64 %i.023.us
%mul.us = mul nsw i64 %i.023.us, %N
br label %for.body3.us
for.body3.us: ; preds = %for.body.us, %for.body3.us
%0 = phi float [ 0.000000e+00, %for.body.us ], [ %add6.us, %for.body3.us ]
%j.021.us = phi i64 [ 0, %for.body.us ], [ %inc.us, %for.body3.us ]
%add.us = add nsw i64 %j.021.us, %mul.us
%arrayidx4.us = getelementptr inbounds float, float* %src, i64 %add.us
%1 = load float, float* %arrayidx4.us, align 4
%add6.us = fadd float %1, %0
%inc.us = add nuw nsw i64 %j.021.us, 1
%exitcond.not = icmp eq i64 %inc.us, %N
br i1 %exitcond.not, label %for.cond3, label %for.body3.us
for.cond3: ; preds = %for.body3.us
%add6.us.lcssa = phi float [ %add6.us, %for.body3.us ]
store float %add6.us.lcssa, float* %arrayidx.us, align 4
%inc8.us = add nuw nsw i64 %i.023.us, 1
%exitcond26.not = icmp eq i64 %inc8.us, %M
br i1 %exitcond26.not, label %exit, label %for.body.us
exit: ; preds = %for.cond3
ret void
}