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[VPlan] Account for dead FOR splice simplification in cost model #131486

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Merged
merged 4 commits into from
Mar 17, 2025
Merged

[VPlan] Account for dead FOR splice simplification in cost model #131486

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3e3a167
[VPlan] Don't cost FOR splice if unused in legacy cost model
lukel97 Mar 16, 2025
3952b01
Move check into planContainsAdditionalSimplifications to account for …
lukel97 Mar 17, 2025
d3d7c03
Remove datalayout
lukel97 Mar 17, 2025
cbc38f7
Use --check-globals=none, tidy up test
lukel97 Mar 17, 2025
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10 changes: 10 additions & 0 deletions llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7467,6 +7467,16 @@ static bool planContainsAdditionalSimplifications(VPlan &Plan,
}
continue;
}
// If a FOR's splice wasn't used it will have been removed, so the VPlan
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nit: might be slightly more compact

Suggested change
// If a FOR's splice wasn't used it will have been removed, so the VPlan
// Unused FOR splices are removed by VPlan transforms, so the VPlan-based cost

// model won't cost it whilst the legacy will.
if (auto *FOR = dyn_cast<VPFirstOrderRecurrencePHIRecipe>(&R)) {
if (none_of(FOR->users(), [](VPUser *U) {
auto *VPI = dyn_cast<VPInstruction>(U);
return VPI && VPI->getOpcode() ==
VPInstruction::FirstOrderRecurrenceSplice;
}))
return true;
}
// The VPlan-based cost model is more accurate for partial reduction and
// comparing against the legacy cost isn't desirable.
if (isa<VPPartialReductionRecipe>(&R))
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111 changes: 111 additions & 0 deletions llvm/test/Transforms/LoopVectorize/X86/pr131359.ll
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@@ -0,0 +1,111 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
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might be worth using a slightly more descriptive name for the file, e.g. `llvm/test/Transforms/LoopVectorize/X86/pr131359-dead-for-splice.ll

; RUN: opt -p loop-vectorize -S %s | FileCheck %s

; If a FOR isn't used the VPInstruction::FirstOrderRecurrenceSplice will be dead
; and won't be costed in the VPlan cost model. Make sure we account for this
; simplifcation in comparison to the legacy cost model.

target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
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nit: Could we remove target datalayout?

target triple = "x86_64"

define void @no_use() {
; CHECK-LABEL: define void @no_use() {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
; CHECK: [[VECTOR_PH]]:
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
; CHECK-NEXT: [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[VECTOR_RECUR:%.*]] = phi <4 x i32> [ <i32 poison, i32 poison, i32 poison, i32 0>, %[[VECTOR_PH]] ], [ [[STEP_ADD:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[VEC_IND:%.*]] = phi <4 x i32> [ <i32 0, i32 1, i32 2, i32 3>, %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[STEP_ADD]] = add <4 x i32> [[VEC_IND]], splat (i32 4)
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 8
; CHECK-NEXT: [[VEC_IND_NEXT]] = add <4 x i32> [[STEP_ADD]], splat (i32 4)
; CHECK-NEXT: [[TMP0:%.*]] = icmp eq i32 [[INDEX_NEXT]], 40
; CHECK-NEXT: br i1 [[TMP0]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[VECTOR_RECUR_EXTRACT:%.*]] = extractelement <4 x i32> [[STEP_ADD]], i32 3
; CHECK-NEXT: br i1 false, label %[[F_EXIT:.*]], label %[[SCALAR_PH]]
; CHECK: [[SCALAR_PH]]:
; CHECK-NEXT: [[SCALAR_RECUR_INIT:%.*]] = phi i32 [ [[VECTOR_RECUR_EXTRACT]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i32 [ 40, %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
; CHECK-NEXT: br label %[[FOR_COND_I:.*]]
; CHECK: [[FOR_COND_I]]:
; CHECK-NEXT: [[D_0_I:%.*]] = phi i32 [ [[SCALAR_RECUR_INIT]], %[[SCALAR_PH]] ], [ [[E_0_I:%.*]], %[[FOR_COND_I]] ]
; CHECK-NEXT: [[E_0_I]] = phi i32 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[INC_I:%.*]], %[[FOR_COND_I]] ]
; CHECK-NEXT: [[INC_I]] = add i32 [[E_0_I]], 1
; CHECK-NEXT: [[EXITCOND_NOT_I:%.*]] = icmp eq i32 [[E_0_I]], 43
; CHECK-NEXT: br i1 [[EXITCOND_NOT_I]], label %[[F_EXIT]], label %[[FOR_COND_I]], !llvm.loop [[LOOP3:![0-9]+]]
; CHECK: [[F_EXIT]]:
; CHECK-NEXT: ret void
;
entry:
br label %for.cond.i

for.cond.i:
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Suggested change
for.cond.i:
loop:

%d.0.i = phi i32 [ 0, %entry ], [ %e.0.i, %for.cond.i ]
%e.0.i = phi i32 [ 0, %entry ], [ %inc.i, %for.cond.i ]
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Might be slightly clearer to use more descriptive names for phis.

Suggested change
%d.0.i = phi i32 [ 0, %entry ], [ %e.0.i, %for.cond.i ]
%e.0.i = phi i32 [ 0, %entry ], [ %inc.i, %for.cond.i ]
%for = phi i32 [ 0, %entry ], [ %e.0.i, %for.cond.i ]
%iv = phi i32 [ 0, %entry ], [ %iv.next, %for.cond.i ]

%inc.i = add i32 %e.0.i, 1
%exitcond.not.i = icmp eq i32 %e.0.i, 43
br i1 %exitcond.not.i, label %f.exit, label %for.cond.i

f.exit:
ret void
}


define void @dead_use() {
; CHECK-LABEL: define void @dead_use() {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
; CHECK: [[VECTOR_PH]]:
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
; CHECK-NEXT: [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[VECTOR_RECUR:%.*]] = phi <4 x i32> [ <i32 poison, i32 poison, i32 poison, i32 0>, %[[VECTOR_PH]] ], [ [[STEP_ADD:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[VEC_IND:%.*]] = phi <4 x i32> [ <i32 0, i32 1, i32 2, i32 3>, %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[STEP_ADD]] = add <4 x i32> [[VEC_IND]], splat (i32 4)
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 8
; CHECK-NEXT: [[VEC_IND_NEXT]] = add <4 x i32> [[STEP_ADD]], splat (i32 4)
; CHECK-NEXT: [[TMP0:%.*]] = icmp eq i32 [[INDEX_NEXT]], 40
; CHECK-NEXT: br i1 [[TMP0]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[VECTOR_RECUR_EXTRACT:%.*]] = extractelement <4 x i32> [[STEP_ADD]], i32 3
; CHECK-NEXT: br i1 false, label %[[F_EXIT:.*]], label %[[SCALAR_PH]]
; CHECK: [[SCALAR_PH]]:
; CHECK-NEXT: [[SCALAR_RECUR_INIT:%.*]] = phi i32 [ [[VECTOR_RECUR_EXTRACT]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i32 [ 40, %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
; CHECK-NEXT: br label %[[FOR_COND_I:.*]]
; CHECK: [[FOR_COND_I]]:
; CHECK-NEXT: [[D_0_I:%.*]] = phi i32 [ [[SCALAR_RECUR_INIT]], %[[SCALAR_PH]] ], [ [[E_0_I:%.*]], %[[FOR_COND_I]] ]
; CHECK-NEXT: [[E_0_I]] = phi i32 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[INC_I:%.*]], %[[FOR_COND_I]] ]
; CHECK-NEXT: [[DEAD:%.*]] = add i32 [[D_0_I]], 1
; CHECK-NEXT: [[INC_I]] = add i32 [[E_0_I]], 1
; CHECK-NEXT: [[EXITCOND_NOT_I:%.*]] = icmp eq i32 [[E_0_I]], 43
; CHECK-NEXT: br i1 [[EXITCOND_NOT_I]], label %[[F_EXIT]], label %[[FOR_COND_I]], !llvm.loop [[LOOP5:![0-9]+]]
; CHECK: [[F_EXIT]]:
; CHECK-NEXT: ret void
;
entry:
br label %for.cond.i

for.cond.i:
%d.0.i = phi i32 [ 0, %entry ], [ %e.0.i, %for.cond.i ]
%e.0.i = phi i32 [ 0, %entry ], [ %inc.i, %for.cond.i ]
%dead = add i32 %d.0.i, 1
%inc.i = add i32 %e.0.i, 1
%exitcond.not.i = icmp eq i32 %e.0.i, 43
br i1 %exitcond.not.i, label %f.exit, label %for.cond.i

f.exit:
ret void
}

;.
; CHECK: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]], [[META2:![0-9]+]]}
; CHECK: [[META1]] = !{!"llvm.loop.isvectorized", i32 1}
; CHECK: [[META2]] = !{!"llvm.loop.unroll.runtime.disable"}
; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META2]], [[META1]]}
; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META1]], [[META2]]}
; CHECK: [[LOOP5]] = distinct !{[[LOOP5]], [[META2]], [[META1]]}
;.
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You might want to use --check-globals=none to remove those change lines

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TIL about that option, that's very handy. Thanks!

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