[llvm] [LoopVectorizer][AArch64] Move getMinTripCountTailFoldingThreshold later. (PR #132170)

[David Sherwood via llvm-commits]

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@@ -1,8 +1,8 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
 ; REQUIRES: asserts
-; RUN: opt -S < %s -p loop-vectorize -debug-only=loop-vectorize -mattr=+sve 2>%t | FileCheck %s --check-prefixes=CHECK,CHECK-VS1
+; RUN: opt -S < %s -p "loop-vectorize,simplifycfg" -debug-only=loop-vectorize -mattr=+sve 2>%t | FileCheck %s --check-prefixes=CHECK,CHECK-VS1
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david-arm wrote:

Same question here - is the simplifycfg really needed to show the desired effect? I tried removing "simplifycfg" and the output is:

```
vector.body:                                      ; preds = %vector.body, %vector.ph
  %index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
  %vec.phi = phi <4 x i32> [ zeroinitializer, %vector.ph ], [ %2, %vector.body ]
  %0 = getelementptr inbounds nuw [4 x i32], ptr %tmp, i64 0, i64 %index
  %1 = getelementptr inbounds nuw i32, ptr %0, i32 0
  %wide.load = load <4 x i32>, ptr %1, align 4
  %2 = add <4 x i32> %vec.phi, %wide.load
  %index.next = add nuw i64 %index, 4
  br i1 true, label %middle.block, label %vector.body, !llvm.loop !7

middle.block:                                     ; preds = %vector.body
  %3 = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> %2)
  br i1 true, label %for.cond.cleanup, label %scalar.ph

scalar.ph:                                        ; preds = %entry, %middle.block
  %bc.resume.val = phi i64 [ 4, %middle.block ], [ 0, %entry ]
  %bc.merge.rdx = phi i32 [ %3, %middle.block ], [ 0, %entry ]
  br label %for.body

for.cond.cleanup:                                 ; preds = %middle.block, %for.body
  %add.lcssa = phi i32 [ %add, %for.body ], [ %3, %middle.block ]
  ret i32 %add.lcssa
```

which is sufficient to show it working as expected, i.e. the vector.body latch unconditionally jumps to middle.block, which unconditionally jumps to for.cond.cleanup. Generally for loop-vectorise tests it's preferred to only test the loop-vectorize pass because simplifycfg may hide latent issues.

https://github.com/llvm/llvm-project/pull/132170