[llvm] [LLVM] Add 'ExpandVariadicsPass' to LTO default pipeline (PR #100479)

[Joseph Huber via llvm-commits]

https://github.com/jhuber6 created https://github.com/llvm/llvm-project/pull/100479

Summary:
This pass expands variadic functions into non-variadic function calls
according to the target ABI. Currently, this is used as the lowering for
the NVPTX, AMDGPU, and WASM targets.

This pass is currently only run late in the target's backend. However,
during LTO we want to run it before the inliner pass so that the
expanded functions can be inlined using standard heuristics. This pass
is a no-op for unsupported targets, so this won't apply to any code that
isn't already using it.


>From 182181e6c251f4c4fa820120ea59fd037e39fb52 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Wed, 24 Jul 2024 17:15:12 -0500
Subject: [PATCH] [LLVM] Add 'ExpandVariadicsPass' to LTO default pipeline

Summary:
This pass expands variadic functions into non-variadic function calls
according to the target ABI. Currently, this is used as the lowering for
the NVPTX, AMDGPU, and WASM targets.

This pass is currently only run late in the target's backend. However,
during LTO we want to run it before the inliner pass so that the
expanded functions can be inlined using standard heuristics. This pass
is a no-op for unsupported targets, so this won't apply to any code that
isn't already using it.
---
 llvm/lib/Passes/PassBuilderPipelines.cpp | 4 ++++
 llvm/test/Other/new-pm-lto-defaults.ll   | 1 +
 2 files changed, 5 insertions(+)

diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index 6f36bdad780ae..757b20dcd6693 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -48,6 +48,7 @@
 #include "llvm/Transforms/IPO/DeadArgumentElimination.h"
 #include "llvm/Transforms/IPO/ElimAvailExtern.h"
 #include "llvm/Transforms/IPO/EmbedBitcodePass.h"
+#include "llvm/Transforms/IPO/ExpandVariadics.h"
 #include "llvm/Transforms/IPO/ForceFunctionAttrs.h"
 #include "llvm/Transforms/IPO/FunctionAttrs.h"
 #include "llvm/Transforms/IPO/GlobalDCE.h"
@@ -1874,6 +1875,9 @@ PassBuilder::buildLTODefaultPipeline(OptimizationLevel Level,
   MPM.addPass(createModuleToFunctionPassAdaptor(std::move(PeepholeFPM),
                                                 PTO.EagerlyInvalidateAnalyses));
 
+  // Lower variadic functions for supported targets prior to inlining.
+  MPM.addPass(ExpandVariadicsPass(ExpandVariadicsMode::Optimize));
+
   // Note: historically, the PruneEH pass was run first to deduce nounwind and
   // generally clean up exception handling overhead. It isn't clear this is
   // valuable as the inliner doesn't currently care whether it is inlining an
diff --git a/llvm/test/Other/new-pm-lto-defaults.ll b/llvm/test/Other/new-pm-lto-defaults.ll
index d451d2897f673..1b345780476b7 100644
--- a/llvm/test/Other/new-pm-lto-defaults.ll
+++ b/llvm/test/Other/new-pm-lto-defaults.ll
@@ -29,6 +29,7 @@
 
 ; CHECK-EP: Running pass: NoOpModulePass
 ; CHECK-O: Running pass: CrossDSOCFIPass
+; CHECK-O-NEXT: Running pass: ExpandVariadicsPass
 ; CHECK-O-NEXT: Running pass: OpenMPOptPass
 ; CHECK-O-NEXT: Running pass: GlobalDCEPass
 ; CHECK-O-NEXT: Running pass: InferFunctionAttrsPass