[LTO] llvm-lto2: Add option to load sample profile

[tobiasvk]

Summary

This exposes LTO's Conf.SampleProfile as a command line option
(-lto-sample-profile-file) for testing via the llvm-lto2 utility.

[danielcdh]

Thanks for doing this! I was about to do the same thing as I have a new patch to that relies on this patch for testing.

llvm/test/LTO/Resolution/X86/Inputs/load-sample-prof.prof

+foo:100:100
+ 1.0: 100 bar:100

llvm/test/LTO/Resolution/X86/load-sample-prof.ll

+; Test that llvm-lto2 handles the -lto-sample-profile-file option
+;
+; RUN: opt -module-summary < %s -o %t.bc
+; RUN: llvm-lto2 run -o %t.out %t.bc -save-temps \
+; RUN:   -r %t.bc,foo,px -r %t.bc,bar,p \
+; RUN:   -lto-sample-profile-file=%S/Inputs/load-sample-prof.prof
+; RUN: llvm-dis %t.out.0.4.opt.bc -o - | FileCheck %s
+;
+; CHECK: !prof
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @foo() local_unnamed_addr !dbg !7 {
+entry:
+  tail call void @bar(), !dbg !10
+  ret void, !dbg !11
+}
+
+declare void @bar() local_unnamed_addr
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 6.0.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test.c", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 6.0.0 "}
+!7 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, isOptimized: true, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null}
+!10 = !DILocation(line: 4, column: 5, scope: !7)
+!11 = !DILocation(line: 5, column: 1, scope: !7)

llvm/tools/llvm-lto2/llvm-lto2.cpp

static cl::opt<std::string>
     OptRemarksOutput("pass-remarks-output",
                      cl::desc("YAML output file for optimization remarks"));
 
 static cl::opt<bool> OptRemarksWithHotness(
     "pass-remarks-with-hotness",
     cl::desc("Whether to include hotness informations in the remarks.\n"
              "Has effect only if -pass-remarks-output is specified."));
 
+static cl::opt<std::string>
+    SamplePGOFile("lto-sample-profile-file",
+                  cl::desc("Specify a SamplePGO profile file"));
+
 static cl::opt<bool>
     UseNewPM("use-new-pm",
              cl::desc("Run LTO passes using the new pass manager"),
              cl::init(false), cl::Hidden);
 
 static void check(Error E, std::string Msg) {
   if (!E)
     return;
static int run(int argc, char **argv) {
   if (SaveTemps)
     check(Conf.addSaveTemps(OutputFilename + "."),
           "Config::addSaveTemps failed");
 
   // Optimization remarks.
   Conf.RemarksFilename = OptRemarksOutput;
   Conf.RemarksWithHotness = OptRemarksWithHotness;
 
+  Conf.SampleProfile = SamplePGOFile;
+
   // Run a custom pipeline, if asked for.
   Conf.OptPipeline = OptPipeline;
   Conf.AAPipeline = AAPipeline;
 
   Conf.OptLevel = OptLevel - '0';
   Conf.UseNewPM = UseNewPM;
   switch (CGOptLevel) {
   case '0':