[llvm-branch-commits] [llvm] [LoopInterchange] Add test for extra reduction use in inner loop (NFC) (PR #203240)

[Ryotaro Kasuga via llvm-branch-commits]

https://github.com/kasuga-fj created https://github.com/llvm/llvm-project/pull/203240

None

>From d75ef1dfa10c9fcc725e0309ff061bffe87678a1 Mon Sep 17 00:00:00 2001
From: Ryotaro Kasuga <kasuga.ryotaro at fujitsu.com>
Date: Thu, 11 Jun 2026 09:09:40 +0000
Subject: [PATCH] [LoopInterchange] Add test for extra reduction use in inner
 loop (NFC)

---
 .../reduction-extra-use-in-inner-loop.ll      | 93 +++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 llvm/test/Transforms/LoopInterchange/reduction-extra-use-in-inner-loop.ll

diff --git a/llvm/test/Transforms/LoopInterchange/reduction-extra-use-in-inner-loop.ll b/llvm/test/Transforms/LoopInterchange/reduction-extra-use-in-inner-loop.ll
new file mode 100644
index 0000000000000..83d93168a9877
--- /dev/null
+++ b/llvm/test/Transforms/LoopInterchange/reduction-extra-use-in-inner-loop.ll
@@ -0,0 +1,93 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt < %s -passes=loop-interchange -loop-interchange-profitabilities=ignore -S | FileCheck %s
+
+; sum = 0;
+; for (i = 0; i < 4; i++)
+;   for (j = 0, sum_i = sum; j < 4; j++) {
+;     sum += A[j][i];
+;     B[j][i] = sum_i;
+;   }
+;
+; Interchanging the loops will become as follows:
+;
+; sum = 0;
+; for (j = 0; j < 4; j++)
+;   for (i = 0, sum_j = sum; i < 4; i++) {
+;     sum_j += A[j][i];
+;     B[j][i] = sum_j;
+;   }
+;
+; This is invalid transformation because the contens of the array `B` will be
+; different.
+;
+; FIXME: The loops are now interchanged.
+;
+define i8 @extra_reduction_use_in_inner(ptr noalias %A, ptr noalias %B) {
+; CHECK-LABEL: define i8 @extra_reduction_use_in_inner(
+; CHECK-SAME: ptr noalias [[A:%.*]], ptr noalias [[B:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[INNER_PREHEADER:.*]]
+; CHECK:       [[OUTER_HEADER_PREHEADER:.*]]:
+; CHECK-NEXT:    br label %[[OUTER_HEADER:.*]]
+; CHECK:       [[OUTER_HEADER]]:
+; CHECK-NEXT:    [[I:%.*]] = phi i64 [ [[I_NEXT:%.*]], %[[OUTER_LATCH:.*]] ], [ 0, %[[OUTER_HEADER_PREHEADER]] ]
+; CHECK-NEXT:    [[SUM_INNER:%.*]] = phi i8 [ [[SUM_NEXT:%.*]], %[[OUTER_LATCH]] ], [ [[SUM:%.*]], %[[OUTER_HEADER_PREHEADER]] ]
+; CHECK-NEXT:    br label %[[INNER_SPLIT1:.*]]
+; CHECK:       [[INNER_PREHEADER]]:
+; CHECK-NEXT:    br label %[[INNER:.*]]
+; CHECK:       [[INNER]]:
+; CHECK-NEXT:    [[J:%.*]] = phi i64 [ [[TMP0:%.*]], %[[INNER_SPLIT:.*]] ], [ 0, %[[INNER_PREHEADER]] ]
+; CHECK-NEXT:    [[SUM]] = phi i8 [ [[SUM_LCSSA:%.*]], %[[INNER_SPLIT]] ], [ 0, %[[INNER_PREHEADER]] ]
+; CHECK-NEXT:    br label %[[OUTER_HEADER_PREHEADER]]
+; CHECK:       [[INNER_SPLIT1]]:
+; CHECK-NEXT:    [[GEP_A:%.*]] = getelementptr [4 x i8], ptr [[A]], i64 [[J]], i64 [[I]]
+; CHECK-NEXT:    [[A:%.*]] = load i8, ptr [[GEP_A]], align 1
+; CHECK-NEXT:    [[SUM_NEXT]] = add i8 [[SUM_INNER]], [[A]]
+; CHECK-NEXT:    [[GEP_B:%.*]] = getelementptr [4 x i8], ptr [[B]], i64 [[J]], i64 [[I]]
+; CHECK-NEXT:    store i8 [[SUM]], ptr [[GEP_B]], align 1
+; CHECK-NEXT:    [[J_NEXT:%.*]] = add i64 [[J]], 1
+; CHECK-NEXT:    [[EC_J:%.*]] = icmp eq i64 [[J_NEXT]], 4
+; CHECK-NEXT:    br label %[[OUTER_LATCH]]
+; CHECK:       [[INNER_SPLIT]]:
+; CHECK-NEXT:    [[SUM_LCSSA]] = phi i8 [ [[SUM_NEXT]], %[[OUTER_LATCH]] ]
+; CHECK-NEXT:    [[TMP0]] = add i64 [[J]], 1
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i64 [[TMP0]], 4
+; CHECK-NEXT:    br i1 [[TMP1]], label %[[EXIT:.*]], label %[[INNER]]
+; CHECK:       [[OUTER_LATCH]]:
+; CHECK-NEXT:    [[I_NEXT]] = add i64 [[I]], 1
+; CHECK-NEXT:    [[EC_I:%.*]] = icmp eq i64 [[I_NEXT]], 4
+; CHECK-NEXT:    br i1 [[EC_I]], label %[[INNER_SPLIT]], label %[[OUTER_HEADER]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    [[RES:%.*]] = phi i8 [ [[SUM_LCSSA]], %[[INNER_SPLIT]] ]
+; CHECK-NEXT:    ret i8 [[RES]]
+;
+entry:
+  br label %outer.header
+
+outer.header:
+  %i = phi i64 [ 0, %entry ], [ %i.next, %outer.latch ]
+  %sum = phi i8 [ 0, %entry ], [ %sum.lcssa, %outer.latch ]
+  br label %inner
+
+inner:
+  %j = phi i64 [ 0, %outer.header ], [ %j.next, %inner ]
+  %sum.inner = phi i8 [ %sum, %outer.header ], [ %sum.next, %inner ]
+  %gep.A = getelementptr [4 x i8], ptr %A, i64 %j, i64 %i
+  %a = load i8, ptr %gep.A
+  %sum.next = add i8 %sum.inner, %a
+  %gep.B = getelementptr [4 x i8], ptr %B, i64 %j, i64 %i
+  store i8 %sum, ptr %gep.B
+  %j.next = add i64 %j, 1
+  %ec.j = icmp eq i64 %j.next, 4
+  br i1 %ec.j, label %outer.latch, label %inner
+
+outer.latch:
+  %sum.lcssa = phi i8 [ %sum.next, %inner ]
+  %i.next = add i64 %i, 1
+  %ec.i = icmp eq i64 %i.next, 4
+  br i1 %ec.i, label %exit, label %outer.header
+
+exit:
+  %res = phi i8 [ %sum.lcssa, %outer.latch ]
+  ret i8 %res
+}