[llvm] [LoopInterchange] Forbid interchange when the dependency is confused (PR #78533)

[Ramkumar Ramachandra via llvm-commits]

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@@ -0,0 +1,55 @@
+; REQUIRES: asserts
+; RUN: opt < %s -passes=loop-interchange -cache-line-size=64 -verify-dom-info -verify-loop-info \
+; RUN:     -S -debug 2>&1 | FileCheck %s
+
+;; Test that a confused dependency in loop should prevent interchange in
+;; loops i and j.
+;;
+;; void test_deps() {
+;;   for (int i = 0; i <= 3; i++)
+;;     for (int j = 0; j <= 3; j++) {
+;;       *f ^= 0x1000;
+;;       c[j][i] = *f;
+;;     }
+;; }
+
+
+; CHECK:  Confused dependency between:
+; CHECK:    store i32 %xor, ptr %arrayidx6, align 4
+; CHECK:    %1 = load i32, ptr %0, align 4
+; CHECK-NOT: Loops interchanged.
+
+ at a = global i32 0, align 4
+ at f = global ptr @a, align 8
+ at c = global [4 x [4 x i32]] zeroinitializer, align 8
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artagnon wrote:

Do these need to be globals? Can they not be passed as arguments to the function?

https://github.com/llvm/llvm-project/pull/78533