[LTO] Support for embedding bitcode section during LTO

Summary:
This adds support for embedding bitcode in a binary during LTO. The libLTO gains supports the `-lto-embed-bitcode` flag. The option allows users of the LTO library to embed a bitcode section. For example, LLD can pass the option via `ld.lld -mllvm=-lto-embed-bitcode`.

This feature allows doing something comparable to `clang -c -fembed-bitcode`, but on the (LTO) linker level. Having bitcode alongside native code has many use-cases. To give an example, the MacOS linker can create a `-bitcode_bundle` section containing bitcode. Also, having this feature built into LLVM is an alternative to 3rd party tools such as [[ https://github.com/travitch/whole-program-llvm | wllvm ]] or [[ https://github.com/SRI-CSL/gllvm | gllvm ]]. As with these tools, this feature simplifies creating "whole-program" llvm bitcode files, but in contrast to wllvm/gllvm it does not rely on a specific llvm frontend/driver.

Patch by Josef Eisl <josef.eisl@oracle.com>

Reviewers: #llvm, #clang, rsmith, pcc, alexshap, tejohnson

Reviewed By: tejohnson

Subscribers: tejohnson, mehdi_amini, inglorion, hiraditya, aheejin, steven_wu, dexonsmith, dang, cfe-commits, llvm-commits, #llvm, #clang

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D68213

1 files changed, 74 insertions, 0 deletions

diff --git a/clang/test/Frontend/x86-embed-bitcode.ll b/clang/test/Frontend/x86-embed-bitcode.ll
new file mode 100644
index 00000000000..709f56bdfe8
--- /dev/null
+++ b/clang/test/Frontend/x86-embed-bitcode.ll
@@ -0,0 +1,74 @@
+; REQUIRES: x86-registered-target
+; check .ll input
+; RUN: %clang_cc1 -triple x86_64-apple-macosx10.10 -emit-llvm \
+; RUN:    -fembed-bitcode=all -x ir %s -o - \
+; RUN:    | FileCheck %s
+; RUN: %clang_cc1 -triple x86_64-apple-macosx10.10 -emit-llvm \
+; RUN:    -fembed-bitcode=marker -x ir %s -o - \
+; RUN:    | FileCheck %s -check-prefix=CHECK-MARKER
+; RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm \
+; RUN:    -fembed-bitcode=all -x ir %s -o - \
+; RUN:    | FileCheck %s -check-prefix=CHECK-ELF
+; RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm \
+; RUN:    -fembed-bitcode=marker -x ir %s -o - \
+; RUN:    | FileCheck %s -check-prefix=CHECK-ELF-MARKER
+; RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm \
+; RUN:    -fembed-bitcode=bitcode -x ir %s -o - \
+; RUN:    | FileCheck %s -check-prefix=CHECK-ELF-ONLY-BITCODE
+
+; check .bc input
+; RUN: %clang_cc1 -triple x86_64-apple-macosx10.10 -emit-llvm-bc \
+; RUN:    -x ir %s -o %t.bc
+; RUN: %clang_cc1 -triple x86_64-apple-macosx10.10 -emit-llvm \
+; RUN:    -fembed-bitcode=all -x ir %t.bc -o - \
+; RUN:    | FileCheck %s
+; RUN: %clang_cc1 -triple x86_64-apple-macosx10.10 -emit-llvm \
+; RUN:    -fembed-bitcode=bitcode -x ir %t.bc -o - \
+; RUN:    | FileCheck %s -check-prefix=CHECK-ONLY-BITCODE
+; RUN: %clang_cc1 -triple x86_64-apple-macosx10.10 -emit-llvm \
+; RUN:    -fembed-bitcode=marker -x ir %t.bc -o - \
+; RUN:    | FileCheck %s -check-prefix=CHECK-MARKER
+
+; run through -fembed-bitcode twice and make sure it doesn't crash
+; RUN: %clang_cc1 -triple x86_64-apple-macosx10.10 -emit-llvm-bc \
+; RUN:    -fembed-bitcode=all -x ir %s -o - \
+; RUN: | %clang_cc1 -triple x86_64-apple-macosx10.10 -emit-llvm \
+; RUN:    -fembed-bitcode=all -x ir - -o /dev/null
+
+; check the magic number of bitcode at the beginning of the string
+; CHECK: @llvm.embedded.module = private constant
+; CHECK: c"\DE\C0\17\0B
+; CHECK: section "__LLVM,__bitcode"
+; CHECK: @llvm.cmdline = private constant
+; CHECK: section "__LLVM,__cmdline"
+
+; CHECK-ELF: @llvm.embedded.module
+; CHECK-ELF: section ".llvmbc"
+; CHECK-ELF: @llvm.cmdline
+; CHECK-ELF: section ".llvmcmd"
+
+; CHECK-ELF-MARKER: @llvm.embedded.module
+; CHECK-ELF-MARKER: constant [0 x i8] zeroinitializer
+; CHECK-ELF-MARKER: @llvm.cmdline
+; CHECK-ELF-MARKER: section ".llvmcmd"
+
+; CHECK-ELF-ONLY-BITCODE: @llvm.embedded.module
+; CHECK-ELF-ONLY-BITCODE: section ".llvmbc"
+; CHECK-ELF-ONLY-BITCODE-NOT: @llvm.cmdline
+; CHECK-ELF-ONLY-BITCODE-NOT: section ".llvmcmd"
+
+; CHECK-ONLY-BITCODE: @llvm.embedded.module = private constant
+; CHECK-ONLY-BITCODE: c"\DE\C0\17\0B
+; CHECK-ONLY-BITCODE: section "__LLVM,__bitcode"
+; CHECK-ONLY-BITCODE-NOT: @llvm.cmdline = private constant
+; CHECK-ONLY-BITCODE-NOT: section "__LLVM,__cmdline"
+
+; CHECK-MARKER: @llvm.embedded.module
+; CHECK-MARKER: constant [0 x i8] zeroinitializer
+; CHECK-MARKER: section "__LLVM,__bitcode"
+; CHECK-MARKER: @llvm.cmdline
+; CHECK-MARKER: section "__LLVM,__cmdline"
+
+define i32 @f0() {
+  ret i32 0
+}