[llvm] [LoopInterchange] Ignore the cost-model, force interchange if legal (PR #148858)

[Florian Hahn via llvm-commits]

================
@@ -0,0 +1,43 @@
+; RUN: opt < %s -passes=loop-interchange -pass-remarks-output=%t -disable-output -loop-interchange-profitabilities=ignore -S
+; RUN: FileCheck --input-file=%t %s
+
+; There should be no reason to interchange this, unless it is forced.
+;
+;     for (int i = 0; i<1024; i++)
+;       for (int j = 0; j<1024; j++)
+;         A[i][j] = 42;
+;
+; CHECK:      --- !Passed
+; CHECK-NEXT: Pass:            loop-interchange
+; CHECK-NEXT: Name:            Interchanged
+; CHECK-NEXT: Function:        f
+; CHECK-NEXT: Args:
+; CHECK-NEXT:   - String:          Loop interchanged with enclosing loop.
+; CHECK-NEXT: ...
+
+ at A = dso_local local_unnamed_addr global [1024 x [1024 x i32]] zeroinitializer, align 4
+
+define dso_local void @f() local_unnamed_addr #0 {
+entry:
+  br label %for.cond1.preheader
+
+for.cond1.preheader:
+  %indvars.iv17 = phi i64 [ 0, %entry ], [ %indvars.iv.next18, %for.cond.cleanup3 ]
+  br label %for.body4
+
+for.cond.cleanup:
+  ret void
+
+for.cond.cleanup3:
+  %indvars.iv.next18 = add nuw nsw i64 %indvars.iv17, 1
+  %exitcond20.not = icmp eq i64 %indvars.iv.next18, 1024
+  br i1 %exitcond20.not, label %for.cond.cleanup, label %for.cond1.preheader
+
+for.body4:
+  %indvars.iv = phi i64 [ 0, %for.cond1.preheader ], [ %indvars.iv.next, %for.body4 ]
+  %arrayidx6 = getelementptr inbounds nuw [1024 x [1024 x i32]], ptr @A, i64 0, i64 %indvars.iv17, i64 %indvars.iv
+  store i32 42, ptr %arrayidx6, align 4
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, 1024
+  br i1 %exitcond.not, label %for.cond.cleanup3, label %for.body4
+}
----------------
fhahn wrote:

It would probably help readability of the test to slightly restructure it

so that a have 

entry:
...

outer.header:
...

inner.header:
....

outer.latch:
...

exit:
...

and compact the value names, e.g. strip redundant `indvars`

https://github.com/llvm/llvm-project/pull/148858