[llvm] [test] Add irreducible CFGs with closed-form block frequencies (PR #213492)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Fangrui Song (MaskRay)

<details>
<summary>Changes</summary>

The functions here have irreducible control flow, but none of them pins down
how mass is divided among the entries of an irreducible region.

Add four cases whose exact frequencies follow from the branch weights:

- equalrows: all blocks share one successor distribution; 5:3:2.
- selfloops: self edges of differing probability; ignoring them, each block
  splits evenly between the other two; 8:5:5.
- unequalrows: symmetric non-header successors, differing header row; 8:3:3.
- nonentry: a member of the region that is not an entry, so its mass is never
  adjusted; 6:4:3.

BFI computes the first two exactly and the last two not. #<!-- -->213488 will
show up as a diff.


---
Full diff: https://github.com/llvm/llvm-project/pull/213492.diff


1 Files Affected:

- (modified) llvm/test/Analysis/BlockFrequencyInfo/irreducible.ll (+106) 


``````````diff
diff --git a/llvm/test/Analysis/BlockFrequencyInfo/irreducible.ll b/llvm/test/Analysis/BlockFrequencyInfo/irreducible.ll
index 71ec83b16a4c4..cb7edf8adb2f3 100644
--- a/llvm/test/Analysis/BlockFrequencyInfo/irreducible.ll
+++ b/llvm/test/Analysis/BlockFrequencyInfo/irreducible.ll
@@ -416,3 +416,109 @@ exit:
 !21 = !{!"branch_weights", i32 2, i32 1}
 !22 = !{!"branch_weights", i32 1, i32 1}
 !23 = !{!"branch_weights", i32 8, i32 1, i32 3, i32 12}
+
+; All blocks share one successor distribution.  Exact lh:o1:o2 = 5:3:2.
+; CHECK-LABEL: block-frequency-info: equalrows
+define void @equalrows(i32 %x) {
+entry:
+; CHECK-NEXT: entry: float = 1.0, int = [[ENTRY:[0-9]+]]
+  switch i32 %x, label %lh [ i32 1, label %o1
+                             i32 2, label %o2 ], !prof !30
+
+lh:
+; CHECK-NEXT: lh: float = 3657.1,
+  switch i32 %x, label %lh [ i32 1, label %o1
+                             i32 2, label %o2 ], !prof !30
+
+o1:
+; CHECK-NEXT: o1: float = 1901.7,
+  switch i32 %x, label %lh [ i32 1, label %o1
+                             i32 2, label %o2 ], !prof !30
+
+o2:
+; CHECK-NEXT: o2: float = 1170.3,
+  switch i32 %x, label %lh [ i32 1, label %o1
+                             i32 2, label %o2 ], !prof !30
+}
+!30 = !{!"branch_weights", i32 5, i32 3, i32 2}
+
+; Self edges of differing probability; ignoring them, each block splits evenly
+; between the other two.  Exact a:b:c = 8:5:5.
+; CHECK-LABEL: block-frequency-info: selfloops
+define void @selfloops(i32 %x) {
+entry:
+; CHECK-NEXT: entry: float = 1.0, int = [[ENTRY:[0-9]+]]
+  switch i32 %x, label %a [ i32 1, label %b
+                            i32 2, label %c ]
+
+a:
+; CHECK-NEXT: a: float = 2730.7,
+  switch i32 %x, label %a [ i32 1, label %b
+                            i32 2, label %c ], !prof !31
+
+b:
+; CHECK-NEXT: b: float = 1706.7,
+  switch i32 %x, label %a [ i32 1, label %b
+                            i32 2, label %c ], !prof !32
+
+c:
+; CHECK-NEXT: c: float = 1706.7,
+  switch i32 %x, label %a [ i32 1, label %b
+                            i32 2, label %c ], !prof !33
+}
+!31 = !{!"branch_weights", i32 2, i32 1, i32 1}
+!32 = !{!"branch_weights", i32 2, i32 1, i32 2}
+!33 = !{!"branch_weights", i32 2, i32 2, i32 1}
+
+; o1 and o2 are symmetric but lh's row differs.  Exact lh:o1:o2 = 8:3:3; BFI
+; computes the values below instead.
+; CHECK-LABEL: block-frequency-info: unequalrows
+define void @unequalrows(i32 %x) {
+entry:
+; CHECK-NEXT: entry: float = 1.0, int = [[ENTRY:[0-9]+]]
+  switch i32 %x, label %lh [ i32 1, label %o1
+                             i32 2, label %o2 ]
+
+lh:
+; CHECK-NEXT: lh: float = 4045.4,
+  switch i32 %x, label %lh [ i32 1, label %o1
+                             i32 2, label %o2 ], !prof !34
+
+o1:
+; CHECK-NEXT: o1: float = 927.08,
+  switch i32 %x, label %lh [ i32 1, label %o1
+                             i32 2, label %o2 ], !prof !35
+
+o2:
+; CHECK-NEXT: o2: float = 927.08,
+  switch i32 %x, label %lh [ i32 1, label %o1
+                             i32 2, label %o2 ], !prof !35
+}
+!34 = !{!"branch_weights", i32 4, i32 3, i32 3}
+!35 = !{!"branch_weights", i32 8, i32 1, i32 1}
+
+; c belongs to the irreducible region but is not an entry, so only a and b get
+; their mass adjusted.  Exact a:b:c = 6:4:3; BFI computes the values below
+; instead.
+; CHECK-LABEL: block-frequency-info: nonentry
+define void @nonentry(i1 %x, i1 %y, i1 %z) {
+entry:
+; CHECK-NEXT: entry: float = 1.0, int = [[ENTRY:[0-9]+]]
+  br i1 %x, label %a, label %b
+
+a:
+; CHECK-NEXT: a: float = 1007.7,
+  br i1 %y, label %c, label %b
+
+c:
+; CHECK-NEXT: c: float = 976.25,
+  br label %a
+
+b:
+; CHECK-NEXT: b: float = 32.508,
+  br i1 %z, label %a, label %exit
+
+exit:
+; CHECK-NEXT: exit: float = 1.0, int = [[ENTRY]]
+  ret void
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/213492