[Hexagon/LoopIdiom] Protect test against O2 changes #144734
Conversation
Protect the pmpy-mod.ll test against O2 pipeline changes, by changing the opt invocation to call exactly the prerequisite passes before calling hexagon-loop-idiom. The context for this change is that a HashRecognize analysis was recently added to LLVM, and the optimization of CRC loops will soon be enabled by default, which would cause pmpy-mod.ll to fail, since the CRC loop would be optimized by a table-lookup before HexagonLoopIdiom has a chance to optimize it using pmpy instructions. HexagonLoopIdiom should probably be removed in the future, preferring the generic middle-end optimization performed by using HashRecognize.
|
@llvm/pr-subscribers-backend-hexagon Author: Ramkumar Ramachandra (artagnon) ChangesProtect the pmpy-mod.ll test against O2 pipeline changes, by changing the opt invocation to call exactly the prerequisite passes before calling hexagon-loop-idiom. The context for this change is that a HashRecognize analysis was recently added to LLVM, and the optimization of CRC loops will soon be enabled by default, which would cause pmpy-mod.ll to fail, since the CRC loop would be optimized by a table-lookup before HexagonLoopIdiom has a chance to optimize it using pmpy instructions. HexagonLoopIdiom should probably be removed in the future, preferring the generic middle-end optimization performed by using HashRecognize. -- 8< -- Full diff: https://github.com/llvm/llvm-project/pull/144734.diff 1 Files Affected:
diff --git a/llvm/test/CodeGen/Hexagon/loop-idiom/pmpy-mod.ll b/llvm/test/CodeGen/Hexagon/loop-idiom/pmpy-mod.ll
index 836a0e110b9e0..e4ab9b131e749 100644
--- a/llvm/test/CodeGen/Hexagon/loop-idiom/pmpy-mod.ll
+++ b/llvm/test/CodeGen/Hexagon/loop-idiom/pmpy-mod.ll
@@ -1,9 +1,5 @@
-; Run -O2 to make sure that all the usual optimizations do happen before
-; the Hexagon loop idiom recognition runs. This is to check that we still
-; get this opportunity regardless of what happens before.
-
-; RUN: opt -O2 -S < %s | FileCheck %s
-; RUN: opt -passes='default<O2>' -S < %s | FileCheck %s
+; RUN: opt -p 'instcombine,simplifycfg,loop-rotate,loop(hexagon-loop-idiom)' \
+; RUN: -S %s | FileCheck %s
target triple = "hexagon"
target datalayout = "e-m:e-p:32:32:32-a:0-n16:32-i64:64:64-i32:32:32-i16:16:16-i1:8:8-f32:32:32-f64:64:64-v32:32:32-v64:64:64-v512:512:512-v1024:1024:1024-v2048:2048:2048"
|
+1 I'd even venture a guess that polynomial multiplication is always better than a table lookup. |
Hm, in that case, I think we'd have to have the optimization turned off by default, until the necessary work is done to emit pmpy instructions on Hexagon, subsuming HexagonLoopIdiom. We can then turn it on by default, and strip HexagonLoopIdiom, I think. |
Maybe for now you could add some sort of a target hook to check if the target wants the CRC optimization? There are other architectures that support polynomial multiplication[1], so adding a target-agnostic support for it would be worthwhile. |
Protect the pmpy-mod.ll test against O2 pipeline changes, by changing the opt invocation to call exactly the prerequisite passes before calling hexagon-loop-idiom. The context for this change is that a HashRecognize analysis was recently added to LLVM, and the optimization of CRC loops will soon be enabled by default, which would cause pmpy-mod.ll to fail, since the CRC loop would be optimized by a table-lookup before HexagonLoopIdiom has a chance to optimize it using pmpy instructions. HexagonLoopIdiom should probably be removed in the future, preferring the generic middle-end optimization performed by using HashRecognize.
-- 8< --
See #143208.