[llvm] 476ca33 - [LTO] Don't apply LTOPostLink module flag during writeMergedModule

[Steven Wu via llvm-commits]

Author: Steven Wu
Date: 2020-08-26T11:17:45-07:00
New Revision: 476ca330894bf42feeb6c13547d14c821f6b8e0a

URL: https://github.com/llvm/llvm-project/commit/476ca330894bf42feeb6c13547d14c821f6b8e0a
DIFF: https://github.com/llvm/llvm-project/commit/476ca330894bf42feeb6c13547d14c821f6b8e0a.diff

LOG: [LTO] Don't apply LTOPostLink module flag during writeMergedModule

For `ld64` which uses legacy LTOCodeGenerator, it relies on
writeMergedModule to perform `ld -r` (generates a linked object file).
If all the inputs to `ld -r` is fullLTO bitcode, `ld64` will linked the
bitcode module, internalize all the symbols and write out another
fullLTO bitcode object file. This bitcode file doesn't have all the
bitcode inputs and it should not have LTOPostLink module flag. It will
also cause error when this bitcode object file is linked with other LTO
object file.
Fix the issue by not applying LTOPostLink flag during writeMergedModule
function. The flag should only be added when all the bitcode are linked
and ready to be optimized.

rdar://problem/58462798

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D84789

Added: 
    

Modified: 
    llvm/lib/LTO/LTOCodeGenerator.cpp
    llvm/test/LTO/ARM/lto-linking-metadata.ll
    llvm/tools/llvm-lto/llvm-lto.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/LTO/LTOCodeGenerator.cpp b/llvm/lib/LTO/LTOCodeGenerator.cpp
index 25ab1404b4e1..aff1977850b8 100644
--- a/llvm/lib/LTO/LTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/LTOCodeGenerator.cpp
@@ -466,8 +466,6 @@ void LTOCodeGenerator::applyScopeRestrictions() {
 
   internalizeModule(*MergedModule, mustPreserveGV);
 
-  MergedModule->addModuleFlag(Module::Error, "LTOPostLink", 1);
-
   ScopeRestrictionsDone = true;
 }
 
@@ -559,6 +557,9 @@ bool LTOCodeGenerator::optimize(bool DisableVerify, bool DisableInline,
   // Mark which symbols can not be internalized
   this->applyScopeRestrictions();
 
+  // Write LTOPostLink flag for passes that require all the modules.
+  MergedModule->addModuleFlag(Module::Error, "LTOPostLink", 1);
+
   // Instantiate the pass manager to organize the passes.
   legacy::PassManager passes;
 

diff  --git a/llvm/test/LTO/ARM/lto-linking-metadata.ll b/llvm/test/LTO/ARM/lto-linking-metadata.ll
index ae6f42ff9be8..75b65ac85bed 100644
--- a/llvm/test/LTO/ARM/lto-linking-metadata.ll
+++ b/llvm/test/LTO/ARM/lto-linking-metadata.ll
@@ -1,7 +1,8 @@
 ; RUN: opt %s -o %t1.bc
 
-; RUN: llvm-lto %t1.bc -o %t1.save.opt -save-merged-module -O1 --exported-symbol=foo
+; RUN: llvm-lto %t1.bc -o %t1.save.opt -save-linked-module -save-merged-module -O1 --exported-symbol=foo
 ; RUN: llvm-dis < %t1.save.opt.merged.bc | FileCheck %s
+; RUN: llvm-dis < %t1.save.opt.linked.bc | FileCheck %s --check-prefix=CHECK-LINKED
 
 ; RUN: llvm-lto2 run %t1.bc -o %t.out.o -save-temps \
 ; RUN:     -r=%t1.bc,foo,pxl
@@ -17,3 +18,6 @@ entry:
 
 ; CHECK: !llvm.module.flags = !{[[MD_NUM:![0-9]+]]}
 ; CHECK: [[MD_NUM]] = !{i32 1, !"LTOPostLink", i32 1}
+
+; CHECK-LINKED: @foo
+; CHECK-LINKED-NOT: LTOPostLink

diff  --git a/llvm/tools/llvm-lto/llvm-lto.cpp b/llvm/tools/llvm-lto/llvm-lto.cpp
index 0bd9078f2d8c..d56cd30cca17 100644
--- a/llvm/tools/llvm-lto/llvm-lto.cpp
+++ b/llvm/tools/llvm-lto/llvm-lto.cpp
@@ -181,6 +181,10 @@ static cl::opt<std::string> ThinLTOGeneratedObjectsDir(
     cl::desc("Save ThinLTO generated object files using filenames created in "
              "the given directory."));
 
+static cl::opt<bool> SaveLinkedModuleFile(
+    "save-linked-module", cl::init(false),
+    cl::desc("Write linked LTO module to file before optimize"));
+
 static cl::opt<bool>
     SaveModuleFile("save-merged-module", cl::init(false),
                    cl::desc("Write merged LTO module to file before CodeGen"));
@@ -1029,6 +1033,15 @@ int main(int argc, char **argv) {
     CodeGen.setFileType(FT.getValue());
 
   if (!OutputFilename.empty()) {
+    if (SaveLinkedModuleFile) {
+      std::string ModuleFilename = OutputFilename;
+      ModuleFilename += ".linked.bc";
+      std::string ErrMsg;
+
+      if (!CodeGen.writeMergedModules(ModuleFilename))
+        error("writing linked module failed.");
+    }
+
     if (!CodeGen.optimize(DisableVerify, DisableInline, DisableGVNLoadPRE,
                           DisableLTOVectorization)) {
       // Diagnostic messages should have been printed by the handler.