Support for function summary index bitcode sections and files.

Summary:
The bitcode format is described in this document:
  https://drive.google.com/file/d/0B036uwnWM6RWdnBLakxmeDdOeXc/view
For more info on ThinLTO see:
  https://sites.google.com/site/llvmthinlto

The first customer is ThinLTO, however the data structures are designed
and named more generally based on prior feedback. There are a few
comments regarding how certain interfaces are used by ThinLTO, and the
options added here to gold currently have ThinLTO-specific names as the
behavior they provoke is currently ThinLTO-specific.

This patch includes support for generating per-module function indexes,
the combined index file via the gold plugin, and several tests
(more are included with the associated clang patch D11908).

Reviewers: dexonsmith, davidxl, joker.eph

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13107

llvm-svn: 249270

llvm/test/Bitcode/thinlto-function-summary.ll

@@ -0,0 +1,45 @@
+; RUN: llvm-as -function-summary < %s | llvm-bcanalyzer -dump | FileCheck %s -check-prefix=BC
+; Check for function summary block/records.
+
+; BC: <FUNCTION_SUMMARY_BLOCK
+; BC-NEXT: <PERMODULE_ENTRY
+; BC-NEXT: <PERMODULE_ENTRY
+; BC-NEXT: <PERMODULE_ENTRY
+; BC-NEXT: </FUNCTION_SUMMARY_BLOCK
+
+; RUN: llvm-as -function-summary < %s | llvm-dis | FileCheck %s
+; Check that this round-trips correctly.
+
+; ModuleID = '<stdin>'
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK: define i32 @foo()
+
+; Function Attrs: nounwind uwtable
+define i32 @foo() #0 {
+entry:
+  ret i32 1
+}
+
+; CHECK: define i32 @bar(i32 %x)
+
+; Function Attrs: nounwind uwtable
+define i32 @bar(i32 %x) #0 {
+entry:
+  ret i32 %x
+}
+
+; Check an anonymous function as well, since in that case only the alias
+; ends up in the value symbol table and having a summary.
+@f = alias void (), void ()* @0   ; <void ()*> [#uses=0]
+@h = external global void ()*     ; <void ()*> [#uses=0]
+
+define internal void @0() nounwind {
+entry:
+  store void()* @0, void()** @h
+        br label %return
+
+return:         ; preds = %entry
+        ret void
+}