[flang] Enable hlfir.sum inlining by default.

[vzakhari]

There is already a LIT test for hlfir.sum inlining that uses
the engineering option. I would like to keep the option
for short period of time to be able to revert
in case of performance regressions that I was not able to see.

[llvmbot]

@llvm/pr-subscribers-flang-fir-hlfir

Author: Slava Zakharin (vzakhari)

Changes

There is already a LIT test for hlfir.sum inlining that uses
the engineering option. I would like to keep the option
for short period of time to be able to revert
in case of performance regressions that I was not able to see.

---

Full diff: https://github.com/llvm/llvm-project/pull/119937.diff

1 Files Affected:

• (modified) flang/lib/Optimizer/HLFIR/Transforms/SimplifyHLFIRIntrinsics.cpp (+2-1)

diff --git a/flang/lib/Optimizer/HLFIR/Transforms/SimplifyHLFIRIntrinsics.cpp b/flang/lib/Optimizer/HLFIR/Transforms/SimplifyHLFIRIntrinsics.cpp
index 3e9d956b6e56dd..a90c5a9ef5a4e5 100644
--- a/flang/lib/Optimizer/HLFIR/Transforms/SimplifyHLFIRIntrinsics.cpp
+++ b/flang/lib/Optimizer/HLFIR/Transforms/SimplifyHLFIRIntrinsics.cpp
@@ -33,7 +33,8 @@ namespace hlfir {
 static llvm::cl::opt<bool>
     simplifySum("flang-simplify-hlfir-sum",
                 llvm::cl::desc("Expand hlfir.sum into an inline sequence"),
-                llvm::cl::init(false));
+                llvm::cl::init(true));
+
 namespace {
 
 class TransposeAsElementalConversion

[vzakhari]

Hi @tblah, could you please verify that there is no exchange2 performance regression any more? I measured it on my side, and performance was the same with and without hlfir.sum inlining.

FWIW, I do see some difference in LLVM inlining:

$ nm noinline.exe | grep digits_2
000000000003b7a0 t _QMbrute_forcePdigits_2.specialized.4
$ nm inline.exe | grep digits_2
000000000003aba0 t _QMbrute_forcePdigits_2.specialized.3

[tblah]

Thank you very much for taking the time to fix our performance regression. I don't see any regression after enabling this pass now.

[vzakhari]

Thank you for checking, Tom!