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[test] Make bt_order_by_weight in switch.ll more robust

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Branch weights are not represented internally linearly with the value in
    the IR. In its current state the test happened to pass, but the branch
    weights for 0,3,6 and 2,5,8,9 were not actually equal.

    $ opt -passes='print<branch-prob>'

    shows that the sum of the branch probabilities going to bb0 and bb2 were not the same.

    Printing analysis results of BPI for function 'bt_order_by_weight':
    ---- Branch Probabilities ----
      edge entry -> bb0 probability is 0x00000003 / 0x80000000 = 0.00%
      edge entry -> bb2 probability is 0x00000004 / 0x80000000 = 0.00%

    with this change:

    Printing analysis results of BPI for function 'bt_order_by_weight':
    ---- Branch Probabilities ----
      edge entry -> bb0 probability is 0x00000004 / 0x80000000 = 0.00%
      edge entry -> bb2 probability is 0x00000004 / 0x80000000 = 0.00%

Reviewed By: hans

Differential Revision: https://reviews.llvm.org/D90273
This commit is contained in:
Arthur Eubanks 2020-10-27 15:47:59 -07:00
parent 7d05974079
commit e89fe0ad6a
1 changed files with 6 additions and 7 deletions
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13
test/CodeGen/X86/switch.ll
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@ -521,11 +521,10 @@ bb2: tail call void @g(i32 2) br label %return
return: ret void
; Cases 1,4,7 have a very large branch weight (which shouldn't overflow), so
; their bit test should come first. 0,3,6 and 2,5,8,9 both have a weight of 12,
; but the latter set has more cases, so should be tested for earlier.
; The bit test on 0,3,6 is unnecessary as all cases cover the rage [0, 9].
; The range check guarantees that cases other than 1,4,7 and 2,5,8,9 must be
; in 0,3,6.
; their bit test should come first. 0,3,6 and 2,5,8,9 both have a weight of 20,
; but the latter set has more cases, so should be tested for earlier. The bit
; test on 0,3,6 is unnecessary as all cases cover the range [0, 9]. The range
; check guarantees that cases other than 1,4,7 and 2,5,8,9 must be in 0,3,6.
; CHECK-LABEL: bt_order_by_weight
; 146 = 2^1 + 2^4 + 2^7
@ -543,11 +542,11 @@ return: ret void
; Default:
i32 1,
; Cases 0,3,6:
i32 4, i32 4, i32 4,
i32 0, i32 0, i32 20,
; Cases 1,4,7:
i32 4294967295, i32 2, i32 4294967295,
; Cases 2,5,8,9:
i32 3, i32 3, i32 3, i32 3}
i32 0, i32 0, i32 0, i32 20}
define void @order_by_weight_and_fallthrough(i32 %x) {
entry: