[LLVM] Add 'ExpandVariadicsPass' to LTO default pipeline

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

llvm/test/Other/new-pm-lto-defaults.ll

@@ -69,6 +69,7 @@
 ; CHECK-O23SZ-NEXT: Running pass: InstCombinePass
 ; CHECK-O23SZ-NEXT: Running pass: AggressiveInstCombinePass
 ; CHECK-EP-Peephole-NEXT: Running pass: NoOpFunctionPass
+; CHECK-O23SZ-NEXT: Running pass: ExpandVariadicsPass
 ; CHECK-O23SZ-NEXT: Running pass: ModuleInlinerWrapperPass
 ; CHECK-O23SZ-NEXT: Running analysis: InlineAdvisorAnalysis
 ; CHECK-O23SZ-NEXT: Running pass: InlinerPass

llvm/test/Transforms/PhaseOrdering/varargs.ll

@@ -0,0 +1,41 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -mtriple=amdgcn-- -S -passes='lto<O2>' < %s | FileCheck %s
+target triple = "amdgcn-amd-amdhsa"
+
+; We use the ExpandVariadics pass to lower variadic functions so they can be
+; inlined.
+
+define i32 @foo() {
+; CHECK-LABEL: define i32 @foo(
+; CHECK-SAME: ) local_unnamed_addr #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    ret i32 6
+;
+entry:
+  %call = tail call i32 (i32, ...) @vararg(i32 poison, i32 noundef 1, i32 noundef 2, i32 noundef 3)
+  ret i32 %call
+}
+
+define internal i32 @vararg(i32 %first, ...) {
+entry:
+  %vlist = alloca ptr, align 8
+  call void @llvm.va_start.p0(ptr %vlist)
+  %vlist.promoted = load ptr, ptr %vlist, align 8
+  %argp.a = getelementptr inbounds i8, ptr %vlist.promoted, i64 4
+  store ptr %argp.a, ptr %vlist, align 8
+  %a = load i32, ptr %vlist.promoted, align 4
+  %argp.b = getelementptr inbounds i8, ptr %vlist.promoted, i64 8
+  store ptr %argp.b, ptr %vlist, align 8
+  %b = load i32, ptr %argp.a, align 4
+  %sum = add nsw i32 %b, %a
+  %argp.c = getelementptr inbounds i8, ptr %vlist.promoted, i64 12
+  store ptr %argp.c, ptr %vlist, align 8
+  %c = load i32, ptr %argp.b, align 4
+  %ret = add nsw i32 %c, %sum
+  call void @llvm.va_end.p0(ptr %vlist)
+  ret i32 %ret
+}
+
+declare void @llvm.va_start.p0(ptr)
+
+declare void @llvm.va_end.p0(ptr)