[Linker] Add directives to support mixing ARM/Thumb module-level inline asm.

Summary:
By prepending `.text .thumb .balign 2` to the module-level inline
assembly from a Thumb module, the assembler will generate the assembly
from that module as Thumb, even if the destination module uses an ARM
triple. Similar directives are used for module-level inline assembly in
ARM modules.

The alignment and instruction set are reset based on the target triple
before emitting the first function label.

Reviewers: olista01, tejohnson, echristo, t.p.northover, rafael

Reviewed By: echristo

Subscribers: aemerson, javed.absar, eraman, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D34622

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307772 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 39 insertions, 2 deletions

diff --git a/lib/Linker/IRMover.cpp b/lib/Linker/IRMover.cpp
index defad190498..f486e525b5e 100644
--- a/lib/Linker/IRMover.cpp
+++ b/lib/Linker/IRMover.cpp
@@ -1256,6 +1256,18 @@ Error IRLinker::linkModuleFlagsMetadata() {
   return Error::success();
 }
 
+/// Return InlineAsm adjusted with target-specific directives if required.
+/// For ARM and Thumb, we have to add directives to select the appropriate ISA
+/// to support mixing module-level inline assembly from ARM and Thumb modules.
+static std::string adjustInlineAsm(const std::string &InlineAsm,
+                                   const Triple &Triple) {
+  if (Triple.getArch() == Triple::thumb || Triple.getArch() == Triple::thumbeb)
+    return ".text\n.balign 2\n.thumb\n" + InlineAsm;
+  if (Triple.getArch() == Triple::arm || Triple.getArch() == Triple::armeb)
+    return ".text\n.balign 4\n.arm\n" + InlineAsm;
+  return InlineAsm;
+}
+
 Error IRLinker::run() {
   // Ensure metadata materialized before value mapping.
   if (SrcM->getMaterializer())
@@ -1293,11 +1305,13 @@ Error IRLinker::run() {
 
   // Append the module inline asm string.
   if (!IsPerformingImport && !SrcM->getModuleInlineAsm().empty()) {
+    std::string SrcModuleInlineAsm = adjustInlineAsm(SrcM->getModuleInlineAsm(),
+                                                     SrcTriple);
     if (DstM.getModuleInlineAsm().empty())
-      DstM.setModuleInlineAsm(SrcM->getModuleInlineAsm());
+      DstM.setModuleInlineAsm(SrcModuleInlineAsm);
     else
       DstM.setModuleInlineAsm(DstM.getModuleInlineAsm() + "\n" +
-                              SrcM->getModuleInlineAsm());
+                              SrcModuleInlineAsm);
   }
 
   // Loop over all of the linked values to compute type mappings.
diff --git a/test/Linker/Inputs/thumb-module-inline-asm.ll b/test/Linker/Inputs/thumb-module-inline-asm.ll
new file mode 100644
index 00000000000..7792ff96d5b
--- /dev/null
+++ b/test/Linker/Inputs/thumb-module-inline-asm.ll
@@ -0,0 +1,3 @@
+target triple = "thumbv7-linux-gnueabihf"
+
+module asm "orn r1, r2, r2"
diff --git a/test/Linker/link-arm-and-thumb-module-inline-asm.ll b/test/Linker/link-arm-and-thumb-module-inline-asm.ll
new file mode 100644
index 00000000000..13779f37ffa
--- /dev/null
+++ b/test/Linker/link-arm-and-thumb-module-inline-asm.ll
@@ -0,0 +1,20 @@
+; This test checks that proper directives to switch between ARM and Thumb mode
+; are added when linking ARM and Thumb modules.
+
+; RUN: llvm-as %s -o %t1.bc
+; RUN: llvm-as %p/Inputs/thumb-module-inline-asm.ll -o %t2.bc
+; RUN: llvm-link %t1.bc %t2.bc -S 2> %t3.out | FileCheck %s
+
+target triple = "armv7-linux-gnueabihf"
+
+module asm "add r1, r2, r2"
+
+; CHECK: .text
+; CHECK-NEXT: .balign 4
+; CHECK-NEXT: .arm
+; CHECK-NEXT: add r1, r2, r2
+; CHECK-NEXT: module asm
+; CHECK-NEXT: .text
+; CHECK-NEXT: .balign 2
+; CHECK-NEXT: .thumb
+; CHECK-NEXT: orn r1, r2, r2