[llvm] [LoopVectorize][NFC] Rewrite tests to check output of vplan cost model (PR #113697)

[David Sherwood via llvm-commits]

================
@@ -1,54 +1,59 @@
 ; REQUIRES: asserts
 ; RUN: opt -mtriple=aarch64 -mattr=+sve \
 ; RUN:     -force-target-instruction-cost=1 -passes=loop-vectorize -S -debug-only=loop-vectorize < %s 2>&1 \
-; RUN:     | FileCheck %s --check-prefixes=GENERIC,VF-VSCALE4
+; RUN:     | FileCheck %s --check-prefixes=GENERIC,VF-VSCALE16
 
 ; RUN: opt -mtriple=aarch64 -mattr=+sve -mcpu=generic \
 ; RUN:     -force-target-instruction-cost=1 -passes=loop-vectorize -S -debug-only=loop-vectorize < %s 2>&1 \
-; RUN:     | FileCheck %s --check-prefixes=GENERIC,VF-VSCALE4
+; RUN:     | FileCheck %s --check-prefixes=GENERIC,VF-VSCALE16
 
 ; RUN: opt -mtriple=aarch64 -mcpu=neoverse-v1 \
 ; RUN:     -force-target-instruction-cost=1 -passes=loop-vectorize -S -debug-only=loop-vectorize < %s 2>&1 \
-; RUN:     | FileCheck %s --check-prefixes=NEOVERSE-V1,VF-VSCALE4
+; RUN:     | FileCheck %s --check-prefixes=NEOVERSE-V1,VF-VSCALE16
 
 ; RUN: opt -mtriple=aarch64 -mcpu=neoverse-n2 \
 ; RUN:     -force-target-instruction-cost=1 -passes=loop-vectorize -S -debug-only=loop-vectorize < %s 2>&1 \
-; RUN:     | FileCheck %s --check-prefixes=NEOVERSE-N2,VF-VSCALE4
+; RUN:     | FileCheck %s --check-prefixes=NEOVERSE-N2,VF-VSCALE16
 
-; RUN: opt -mtriple=aarch64 -mcpu=neoverse-n2 \
+; RUN: opt -mtriple=aarch64 -mcpu=neoverse-v2 \
 ; RUN:     -force-target-instruction-cost=1 -passes=loop-vectorize -S -debug-only=loop-vectorize < %s 2>&1 \
-; RUN:     | FileCheck %s --check-prefixes=NEOVERSE-N2,VF-VSCALE4
+; RUN:     | FileCheck %s --check-prefixes=NEOVERSE-V2,VF-16
+
+; GENERIC: Cost for VF vscale x 2: 11
+; GENERIC: Cost for VF vscale x 4: 11
+; GENERIC: LV: Selecting VF: vscale x 16
 
-; GENERIC: LV: Vector loop of width vscale x 2 costs: 3 (assuming a minimum vscale of 2).
-; GENERIC: LV: Vector loop of width vscale x 4 costs: 1 (assuming a minimum vscale of 2).
+; NEOVERSE-V1: Cost for VF vscale x 2: 11
+; NEOVERSE-V1: Cost for VF vscale x 4: 11
+; NEOVERSE-V1: LV: Selecting VF: vscale x 16
 
-; NEOVERSE-V1: LV: Vector loop of width vscale x 2 costs: 3 (assuming a minimum vscale of 2).
-; NEOVERSE-V1: LV: Vector loop of width vscale x 4 costs: 1 (assuming a minimum vscale of 2).
+; NEOVERSE-N2: Cost for VF vscale x 2: 11
+; NEOVERSE-N2: Cost for VF vscale x 4: 11
+; NEOVERSE-N2: LV: Selecting VF: vscale x 16
 
-; NEOVERSE-N2: LV: Vector loop of width vscale x 2 costs: 6 (assuming a minimum vscale of 1).
-; NEOVERSE-N2: LV: Vector loop of width vscale x 4 costs: 3 (assuming a minimum vscale of 1).
+; NEOVERSE-V2: Cost for VF vscale x 2: 11
+; NEOVERSE-V2: Cost for VF vscale x 4: 11
+; NEOVERSE-V2: LV: Selecting VF: 16
 
-; VF-4: <4 x i32>
-; VF-VSCALE4: <16 x i32>
+; VF-16: <16 x i8>
+; VF-VSCALE16: <vscale x 16 x i8>
----------------
david-arm wrote:

I think this test was falling foul of the difference in max vector bandwidth behaviour between NEON and SVE, but perhaps the behaviour is now the same on the latest version of LLVM?

The problem I had was for NEON we'd choose a maximum VF of 16 on neoverse-v1 vs a max of VF=vscale x 4, due to the zext from i8 to i32. This didn't matter for the legacy cost model because the output was divided by the VF, i.e.

```
NEOVERSE-V1: LV: Vector loop of width vscale x 4 costs: 1 (assuming a minimum vscale of 2).
```

That meant we could effectively test for the vscale tuning value, since the final cost = absolute cost / estimated VF. With the new cost model it only prints out the absolute cost per VF so the only way to detect that vscale is having an effect is to check for the chosen VF. But with the old version of the test when NEON is maximising the bandwidth and SVE isn't we end up choosing VF=16.

I wasn't sure if it was worth modifying the new cost model output to show the per-lane cost or not. @fhahn any thoughts?

Another option is to actually get the vectoriser to print out what it estimates the runtime VF to be?

https://github.com/llvm/llvm-project/pull/113697