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[LoopInterchange] Ignore the cost-model, force interchange if legal #148858

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Merged
merged 10 commits into from
Jul 18, 2025
Merged

[LoopInterchange] Ignore the cost-model, force interchange if legal #148858

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db9c37e
[LoopInterchange] Ignore the cost-model, force interchange if legal
sjoerdmeijer Jul 15, 2025
fe979ea
Add an ignore value to the existing profitability option.
sjoerdmeijer Jul 16, 2025
5bb2158
Remove the old option, we don't need that anymore, left it accidentally
sjoerdmeijer Jul 17, 2025
1e8e667
Fix formatting.
sjoerdmeijer Jul 17, 2025
6a3b3f0
Update llvm/test/Transforms/LoopInterchange/force-interchange.ll
sjoerdmeijer Jul 17, 2025
82a3043
Addressed review comments
sjoerdmeijer Jul 17, 2025
58a6efb
Debug message when ignore has no effect.
sjoerdmeijer Jul 17, 2025
057d32b
noDuplicateRulesAndIgnore: assert that ignore doesn't appear in a list.
sjoerdmeijer Jul 18, 2025
b5bc6d1
Renamed test case labels and variables.
sjoerdmeijer Jul 18, 2025
1736f1f
Added llvm_unreachable
sjoerdmeijer Jul 18, 2025
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7 changes: 6 additions & 1 deletion llvm/lib/Transforms/Scalar/LoopInterchange.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,10 @@ static cl::opt<unsigned int> MaxMemInstrCount(
"in the dependency matrix. Higher value may lead to more interchanges "
"at the cost of compile-time"));

static cl::opt<bool> ForceLoopInterchange(
"loop-interchange-force", cl::init(false), cl::Hidden,
cl::desc("Ignore the cost model, and force interchange if it is legal"));

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@madhur13490 madhur13490 Jul 15, 2025

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Would it be better if we call it -loop-interchange-ignore-cost-model? -force seems it covers wider scenarios.

namespace {

using LoopVector = SmallVector<Loop *, 8>;
Expand Down Expand Up @@ -599,7 +603,8 @@ struct LoopInterchange {
}
LLVM_DEBUG(dbgs() << "Loops are legal to interchange\n");
LoopInterchangeProfitability LIP(OuterLoop, InnerLoop, SE, ORE);
if (!LIP.isProfitable(InnerLoop, OuterLoop, InnerLoopId, OuterLoopId,
if (!ForceLoopInterchange &&
!LIP.isProfitable(InnerLoop, OuterLoop, InnerLoopId, OuterLoopId,
DependencyMatrix, CCM)) {
LLVM_DEBUG(dbgs() << "Interchanging loops not profitable.\n");
return false;
Expand Down
4 changes: 4 additions & 0 deletions llvm/test/Transforms/LoopInterchange/profitability-vectorization.ll
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Expand Up @@ -2,6 +2,10 @@
; RUN: -pass-remarks-output=%t -disable-output
; RUN: FileCheck -input-file %t --check-prefix=PROFIT-CACHE %s

; RUN: opt < %s -passes=loop-interchange -cache-line-size=64 \
; RUN: -pass-remarks-output=%t -disable-output -loop-interchange-force=true
; RUN: FileCheck -input-file %t --check-prefix=PROFIT-VEC %s
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@kasuga-fj kasuga-fj Jul 15, 2025

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Could you please add another test case? Interchanging the loops in this test would be beneficial in perspective of vectorizatoin (i.e., isProfitableForVectorization returns true in this case) because it makes the innermost loop vectorizable. It would be ideal to add a case where interchanging is definitely unprofitable.


; RUN: opt < %s -passes=loop-interchange -cache-line-size=64 \
; RUN: -pass-remarks-output=%t -disable-output -loop-interchange-profitabilities=vectorize,cache,instorder
; RUN: FileCheck -input-file %t --check-prefix=PROFIT-VEC %s
Expand Down
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