[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
+
+define void @test_deps() {
+entry:
+  %0 = load ptr, ptr @f, align 8
+  br label %for.cond1.preheader
+
+; Loop:
+for.cond1.preheader:                              ; preds = %entry, %for.cond.cleanup3
+  %indvars.iv16 = phi i64 [ 0, %entry ], [ %indvars.iv.next17, %for.cond.cleanup3 ]
+  br label %for.body4
+
+for.cond.cleanup3:                                ; preds = %for.body4
+  %indvars.iv.next17 = add nuw nsw i64 %indvars.iv16, 1
+  %exitcond18 = icmp ne i64 %indvars.iv.next17, 4
+  br i1 %exitcond18, label %for.cond1.preheader, label %for.cond.cleanup
+
+for.body4:                                        ; preds = %for.cond1.preheader, %for.body4
+  %indvars.iv = phi i64 [ 0, %for.cond1.preheader ], [ %indvars.iv.next, %for.body4 ]
+  %1 = load i32, ptr %0, align 4
+  %xor = xor i32 %1, 4096
+  store i32 %xor, ptr %0, align 4
+  %arrayidx6 = getelementptr inbounds [4 x [4 x i32]], ptr @c, i64 0, i64 %indvars.iv, i64 %indvars.iv16
+  store i32 %xor, ptr %arrayidx6, align 4
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond = icmp ne i64 %indvars.iv.next, 4
+  br i1 %exitcond, label %for.body4, label %for.cond.cleanup3
----------------
artagnon wrote:

It would be nice if the test were cleaned up a bit. Example: s/indvars.iv/iv.inner/, s/for.body.4/inner.loop/, s/for.cond1.preheader/outer.loop/?

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