[llvm] [LoopUnroll] Make the list of supported recurrence kinds inclusive. (PR #210957)
David Green via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 23 03:18:41 PDT 2026
https://github.com/davemgreen updated https://github.com/llvm/llvm-project/pull/210957
>From 693e966883e6d392d8cbc048224a22d6cf26c768 Mon Sep 17 00:00:00 2001
From: David Green <david.green at arm.com>
Date: Tue, 21 Jul 2026 12:53:19 +0100
Subject: [PATCH 1/3] [LoopUnroll] Make the list of supported recurrence kinds
inclusive.
This excludes Sub, AddChainWithSubs, FSub and FAddChainWithSubs recurrence
kinds by making the list of supported types opt-in as opposed to opt-out. This
will hopefully mean that as more recurrence kinds are added in the future, the
list supported by the unrolling remains valid.
Fixes #201065
---
llvm/lib/Transforms/Utils/LoopUnroll.cpp | 14 ++++--
.../LoopUnroll/partial-unroll-reductions.ll | 47 +++++++++++++++++++
2 files changed, 57 insertions(+), 4 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 1f9f340a9cb31..1b2f7ead74972 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -1719,10 +1719,16 @@ llvm::canParallelizeReductionWhenUnrolling(PHINode &Phi, Loop *L,
if (RdxDesc.hasUsesOutsideReductionChain())
return std::nullopt;
RecurKind RK = RdxDesc.getRecurrenceKind();
- // Skip unsupported reductions.
- // TODO: Handle any-of and find-last reductions.
- if (RecurrenceDescriptor::isAnyOfRecurrenceKind(RK) ||
- RecurrenceDescriptor::isFindRecurrenceKind(RK))
+ // Skip unsupported reductions, including sub, any-of and find-last.
+ // TODO: Handle sub, any-of and find-last reductions.
+ if (RK != RecurKind::Add && RK != RecurKind::Mul && RK != RecurKind::Or &&
+ RK != RecurKind::And && RK != RecurKind::Xor && RK != RecurKind::SMin &&
+ RK != RecurKind::SMax && RK != RecurKind::UMin && RK != RecurKind::UMax &&
+ RK != RecurKind::FAdd && RK != RecurKind::FMul && RK != RecurKind::FMin &&
+ RK != RecurKind::FMax && RK != RecurKind::FMinNum &&
+ RK != RecurKind::FMaxNum && RK != RecurKind::FMinimum &&
+ RK != RecurKind::FMaximum && RK != RecurKind::FMinimumNum &&
+ RK != RecurKind::FMaximumNum && RK != RecurKind::FMulAdd)
return std::nullopt;
if (RdxDesc.hasExactFPMath())
diff --git a/llvm/test/Transforms/LoopUnroll/partial-unroll-reductions.ll b/llvm/test/Transforms/LoopUnroll/partial-unroll-reductions.ll
index aecdb192cc3a9..ba7b853f952c1 100644
--- a/llvm/test/Transforms/LoopUnroll/partial-unroll-reductions.ll
+++ b/llvm/test/Transforms/LoopUnroll/partial-unroll-reductions.ll
@@ -741,3 +741,50 @@ loop:
exit:
ret i32 %select.data
}
+
+define i32 @test_sub(ptr %src, i64 %n, i32 %start) {
+; CHECK-LABEL: define i32 @test_sub(
+; CHECK-SAME: ptr [[SRC:%.*]], i64 [[N:%.*]], i32 [[START:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[LOOP:.*]]
+; CHECK: [[LOOP]]:
+; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[IV_NEXT_3:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[RDX:%.*]] = phi i32 [ [[START]], %[[ENTRY]] ], [ [[RDX_NEXT_3:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[IV_NEXT:%.*]] = add nuw nsw i64 [[IV]], 1
+; CHECK-NEXT: [[GEP_SRC:%.*]] = getelementptr i32, ptr [[SRC]], i64 [[IV]]
+; CHECK-NEXT: [[L:%.*]] = load i32, ptr [[GEP_SRC]], align 1
+; CHECK-NEXT: [[RDX_NEXT:%.*]] = sub i32 [[RDX]], [[L]]
+; CHECK-NEXT: [[IV_NEXT_1:%.*]] = add nuw nsw i64 [[IV]], 2
+; CHECK-NEXT: [[GEP_SRC_1:%.*]] = getelementptr i32, ptr [[SRC]], i64 [[IV_NEXT]]
+; CHECK-NEXT: [[L_1:%.*]] = load i32, ptr [[GEP_SRC_1]], align 1
+; CHECK-NEXT: [[RDX_2:%.*]] = sub i32 [[RDX_NEXT]], [[L_1]]
+; CHECK-NEXT: [[IV_NEXT_2:%.*]] = add nuw nsw i64 [[IV]], 3
+; CHECK-NEXT: [[GEP_SRC_2:%.*]] = getelementptr i32, ptr [[SRC]], i64 [[IV_NEXT_1]]
+; CHECK-NEXT: [[L_2:%.*]] = load i32, ptr [[GEP_SRC_2]], align 1
+; CHECK-NEXT: [[RDX_NEXT_2:%.*]] = sub i32 [[RDX_2]], [[L_2]]
+; CHECK-NEXT: [[IV_NEXT_3]] = add nuw nsw i64 [[IV]], 4
+; CHECK-NEXT: [[GEP_SRC_3:%.*]] = getelementptr i32, ptr [[SRC]], i64 [[IV_NEXT_2]]
+; CHECK-NEXT: [[L_3:%.*]] = load i32, ptr [[GEP_SRC_3]], align 1
+; CHECK-NEXT: [[RDX_NEXT_3]] = sub i32 [[RDX_NEXT_2]], [[L_3]]
+; CHECK-NEXT: [[EC_3:%.*]] = icmp ne i64 [[IV_NEXT_3]], 1000
+; CHECK-NEXT: br i1 [[EC_3]], label %[[LOOP]], label %[[EXIT:.*]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: [[BIN_RDX2:%.*]] = phi i32 [ [[RDX_NEXT_3]], %[[LOOP]] ]
+; CHECK-NEXT: ret i32 [[BIN_RDX2]]
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+ %rdx = phi i32 [ %start, %entry ], [ %rdx.next, %loop ]
+ %iv.next = add i64 %iv, 1
+ %gep.src = getelementptr i32, ptr %src, i64 %iv
+ %l = load i32 , ptr %gep.src, align 1
+ %rdx.next = sub i32 %rdx, %l
+ %ec = icmp ne i64 %iv.next, 1000
+ br i1 %ec, label %loop, label %exit
+
+exit:
+ ret i32 %rdx.next
+}
>From 99fe4673c0b96ee21e0be77e2d60c2aa66968247 Mon Sep 17 00:00:00 2001
From: David Green <david.green at arm.com>
Date: Thu, 23 Jul 2026 10:56:27 +0100
Subject: [PATCH 2/3] Change to use any_of
---
llvm/lib/Transforms/Utils/LoopUnroll.cpp | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 1b2f7ead74972..1c01e6bbacd6c 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -1721,14 +1721,15 @@ llvm::canParallelizeReductionWhenUnrolling(PHINode &Phi, Loop *L,
RecurKind RK = RdxDesc.getRecurrenceKind();
// Skip unsupported reductions, including sub, any-of and find-last.
// TODO: Handle sub, any-of and find-last reductions.
- if (RK != RecurKind::Add && RK != RecurKind::Mul && RK != RecurKind::Or &&
- RK != RecurKind::And && RK != RecurKind::Xor && RK != RecurKind::SMin &&
- RK != RecurKind::SMax && RK != RecurKind::UMin && RK != RecurKind::UMax &&
- RK != RecurKind::FAdd && RK != RecurKind::FMul && RK != RecurKind::FMin &&
- RK != RecurKind::FMax && RK != RecurKind::FMinNum &&
- RK != RecurKind::FMaxNum && RK != RecurKind::FMinimum &&
- RK != RecurKind::FMaximum && RK != RecurKind::FMinimumNum &&
- RK != RecurKind::FMaximumNum && RK != RecurKind::FMulAdd)
+ static const auto ValidRKs = {
+ RecurKind::Add, RecurKind::Mul, RecurKind::Or,
+ RecurKind::And, RecurKind::Xor, RecurKind::SMin,
+ RecurKind::SMax, RecurKind::UMin, RecurKind::UMax,
+ RecurKind::FAdd, RecurKind::FMul, RecurKind::FMin,
+ RecurKind::FMax, RecurKind::FMinNum, RecurKind::FMaxNum,
+ RecurKind::FMinimum, RecurKind::FMaximum, RecurKind::FMinimumNum,
+ RecurKind::FMaximumNum, RecurKind::FMulAdd};
+ if (!any_of(ValidRKs, equal_to(RK)))
return std::nullopt;
if (RdxDesc.hasExactFPMath())
>From 0ac00ee6e86fbf35d37a1c0575d64fa158033279 Mon Sep 17 00:00:00 2001
From: David Green <david.green at arm.com>
Date: Thu, 23 Jul 2026 11:18:28 +0100
Subject: [PATCH 3/3] Move comment
---
llvm/lib/Transforms/Utils/LoopUnroll.cpp | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 1c01e6bbacd6c..faf05b657fa2a 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -1719,8 +1719,6 @@ llvm::canParallelizeReductionWhenUnrolling(PHINode &Phi, Loop *L,
if (RdxDesc.hasUsesOutsideReductionChain())
return std::nullopt;
RecurKind RK = RdxDesc.getRecurrenceKind();
- // Skip unsupported reductions, including sub, any-of and find-last.
- // TODO: Handle sub, any-of and find-last reductions.
static const auto ValidRKs = {
RecurKind::Add, RecurKind::Mul, RecurKind::Or,
RecurKind::And, RecurKind::Xor, RecurKind::SMin,
@@ -1729,6 +1727,8 @@ llvm::canParallelizeReductionWhenUnrolling(PHINode &Phi, Loop *L,
RecurKind::FMax, RecurKind::FMinNum, RecurKind::FMaxNum,
RecurKind::FMinimum, RecurKind::FMaximum, RecurKind::FMinimumNum,
RecurKind::FMaximumNum, RecurKind::FMulAdd};
+ // Skip unsupported reductions, including sub, any-of and find-last.
+ // TODO: Handle sub, any-of and find-last reductions.
if (!any_of(ValidRKs, equal_to(RK)))
return std::nullopt;
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