[ThinLTO] Serialize WithGlobalValueDeadStripping index flag for distributed backends

Summary:
A recent fix to drop dead symbols (r323633) did not work for ThinLTO
distributed backends because we lose the WithGlobalValueDeadStripping
set on the index during the thin link. This patch adds a new flags
record to the bitcode format for the index, and serializes this flag
for the combined index (it would always be 0 for the per-module index
generated by the compile step, so no need to serialize the new flags
record there until/unless we add another flag that applies to the
per-module indexes).

Generally this flag should always be set for the distributed backends,
which are necessarily performed after the thin link. However, if we were
to simply set this flag on the index applied to the distributed backends
(invoked via clang), we would lose the ability to disable dead stripping
via -compute-dead=false for debugging purposes.

Reviewers: grimar, pcc

Subscribers: mehdi_amini, inglorion, eraman, llvm-commits

Differential Revision: https://reviews.llvm.org/D42799

llvm-svn: 324444

13 files changed, 48 insertions, 0 deletions

diff --git a/llvm/include/llvm/Bitcode/LLVMBitCodes.h b/llvm/include/llvm/Bitcode/LLVMBitCodes.h
index 7a457744db7..ab76b0ba683 100644
--- a/llvm/include/llvm/Bitcode/LLVMBitCodes.h
+++ b/llvm/include/llvm/Bitcode/LLVMBitCodes.h
@@ -261,6 +261,8 @@ enum GlobalValueSummarySymtabCodes {
   //                   numrefs x valueid,
   //                   n x (valueid, relblockfreq)]
   FS_PERMODULE_RELBF = 19,
+  // Index-wide flags
+  FS_FLAGS = 20,
 };
 
 enum MetadataCodes {
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 9cf1302b030..6da39a76310 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -5133,6 +5133,16 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
     switch (BitCode) {
     default: // Default behavior: ignore.
       break;
+    case bitc::FS_FLAGS: {  // [flags]
+      uint64_t Flags = Record[0];
+      // Scan flags (set only on the combined index).
+      assert(Flags <= 1 && "Unexpected bits in flag");
+
+      // 1 bit: WithGlobalValueDeadStripping flag.
+      if (Flags & 0x1)
+        TheIndex.setWithGlobalValueDeadStripping();
+      break;
+    }
     case bitc::FS_VALUE_GUID: { // [valueid, refguid]
       uint64_t ValueID = Record[0];
       GlobalValue::GUID RefGUID = Record[1];
diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 76add4f7da3..fd9cde17847 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -3552,6 +3552,11 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   Stream.EnterSubblock(bitc::GLOBALVAL_SUMMARY_BLOCK_ID, 3);
   Stream.EmitRecord(bitc::FS_VERSION, ArrayRef<uint64_t>{INDEX_VERSION});
 
+  // Write the index flags. Currently we only write a single flag, the value of
+  // withGlobalValueDeadStripping, which only applies to the combined index.
+  Stream.EmitRecord(bitc::FS_FLAGS,
+                    ArrayRef<uint64_t>{Index.withGlobalValueDeadStripping()});
+
   for (const auto &GVI : valueIds()) {
     Stream.EmitRecord(bitc::FS_VALUE_GUID,
                       ArrayRef<uint64_t>{GVI.second, GVI.first});
diff --git a/llvm/test/Bitcode/thinlto-alias.ll b/llvm/test/Bitcode/thinlto-alias.ll
index 668c5cd22dc..a5020ff7119 100644
--- a/llvm/test/Bitcode/thinlto-alias.ll
+++ b/llvm/test/Bitcode/thinlto-alias.ll
@@ -22,6 +22,7 @@
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
+; COMBINED-NEXT:    <FLAGS
 ; See if the call to analias is registered, using the expected value id.
 ; COMBINED-NEXT:    <VALUE_GUID op0=[[ALIASID:[0-9]+]] op1=-5751648690987223394/>
 ; COMBINED-NEXT:    <VALUE_GUID
diff --git a/llvm/test/Bitcode/thinlto-deadstrip-flag.ll b/llvm/test/Bitcode/thinlto-deadstrip-flag.ll
new file mode 100644
index 00000000000..5330a25dbf1
--- /dev/null
+++ b/llvm/test/Bitcode/thinlto-deadstrip-flag.ll
@@ -0,0 +1,20 @@
+; REQUIRES: x86-registered-target
+; RUN: opt -module-summary %s -o %t.o
+
+; Ensure dead stripping performed flag is set on distributed index
+; RUN: llvm-lto2 run %t.o -o %t.out -thinlto-distributed-indexes \
+; RUN:		-r %t.o,glob,plx
+; RUN: llvm-bcanalyzer -dump %t.o.thinlto.bc | FileCheck %s --check-prefix=WITHDEAD
+; WITHDEAD: <FLAGS op0=1/>
+
+; Ensure dead stripping performed flag is not set on distributed index
+; when option used to disable dead stripping computation.
+; RUN: llvm-lto2 run %t.o -o %t.out -thinlto-distributed-indexes \
+; RUN:		-r %t.o,glob,plx -compute-dead=false
+; RUN: llvm-bcanalyzer -dump %t.o.thinlto.bc | FileCheck %s --check-prefix=NODEAD
+; NODEAD: <FLAGS op0=0/>
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@glob = global i32 0
diff --git a/llvm/test/Bitcode/thinlto-function-summary-callgraph-pgo.ll b/llvm/test/Bitcode/thinlto-function-summary-callgraph-pgo.ll
index 9376e801765..bb3e8e97835 100644
--- a/llvm/test/Bitcode/thinlto-function-summary-callgraph-pgo.ll
+++ b/llvm/test/Bitcode/thinlto-function-summary-callgraph-pgo.ll
@@ -24,6 +24,7 @@
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
+; COMBINED-NEXT:    <FLAGS
 ; COMBINED-NEXT:    <VALUE_GUID op0=[[FUNCID:[0-9]+]] op1=7289175272376759421/>
 ; COMBINED-NEXT:    <VALUE_GUID
 ; COMBINED-NEXT:    <COMBINED
diff --git a/llvm/test/Bitcode/thinlto-function-summary-callgraph-profile-summary.ll b/llvm/test/Bitcode/thinlto-function-summary-callgraph-profile-summary.ll
index d0cfa093ecd..9d4ef4cd264 100644
--- a/llvm/test/Bitcode/thinlto-function-summary-callgraph-profile-summary.ll
+++ b/llvm/test/Bitcode/thinlto-function-summary-callgraph-profile-summary.ll
@@ -37,6 +37,7 @@
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
+; COMBINED-NEXT:    <FLAGS
 ; COMBINED-NEXT:    <VALUE_GUID
 ; COMBINED-NEXT:    <VALUE_GUID
 ; COMBINED-NEXT:    <VALUE_GUID
diff --git a/llvm/test/Bitcode/thinlto-function-summary-callgraph-sample-profile-summary.ll b/llvm/test/Bitcode/thinlto-function-summary-callgraph-sample-profile-summary.ll
index 4085174ae27..8793a08d3bf 100644
--- a/llvm/test/Bitcode/thinlto-function-summary-callgraph-sample-profile-summary.ll
+++ b/llvm/test/Bitcode/thinlto-function-summary-callgraph-sample-profile-summary.ll
@@ -39,6 +39,7 @@
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
+; COMBINED-NEXT:    <FLAGS
 ; COMBINED-NEXT:    <VALUE_GUID
 ; COMBINED-NEXT:    <VALUE_GUID
 ; COMBINED-NEXT:    <VALUE_GUID
diff --git a/llvm/test/Bitcode/thinlto-function-summary-callgraph.ll b/llvm/test/Bitcode/thinlto-function-summary-callgraph.ll
index 1389710e18d..8025eee5929 100644
--- a/llvm/test/Bitcode/thinlto-function-summary-callgraph.ll
+++ b/llvm/test/Bitcode/thinlto-function-summary-callgraph.ll
@@ -26,6 +26,7 @@
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
+; COMBINED-NEXT:    <FLAGS
 ; Only 2 VALUE_GUID since reference to undefinedglob should not be included in
 ; combined index.
 ; COMBINED-NEXT:    <VALUE_GUID op0=[[FUNCID:[0-9]+]] op1=7289175272376759421/>
diff --git a/llvm/test/Bitcode/thinlto-function-summary-originalnames.ll b/llvm/test/Bitcode/thinlto-function-summary-originalnames.ll
index afc9772484e..6387e6322ec 100644
--- a/llvm/test/Bitcode/thinlto-function-summary-originalnames.ll
+++ b/llvm/test/Bitcode/thinlto-function-summary-originalnames.ll
@@ -5,6 +5,7 @@
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
+; COMBINED-NEXT:    <FLAGS
 ; COMBINED-NEXT:    <VALUE_GUID {{.*}} op1=4947176790635855146/>
 ; COMBINED-NEXT:    <VALUE_GUID {{.*}} op1=-6591587165810580810/>
 ; COMBINED-NEXT:    <VALUE_GUID {{.*}} op1=-4377693495213223786/>
diff --git a/llvm/test/tools/gold/X86/thinlto.ll b/llvm/test/tools/gold/X86/thinlto.ll
index 13d1bf3c46f..54cee219352 100644
--- a/llvm/test/tools/gold/X86/thinlto.ll
+++ b/llvm/test/tools/gold/X86/thinlto.ll
@@ -95,6 +95,7 @@
 ; BACKEND1-NEXT: </MODULE_STRTAB_BLOCK
 ; BACKEND1-NEXT: <GLOBALVAL_SUMMARY_BLOCK
 ; BACKEND1-NEXT: <VERSION
+; BACKEND1-NEXT: <FLAGS
 ; BACKEND1-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
 ; BACKEND1-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
 ; BACKEND1-NEXT: <COMBINED
@@ -108,6 +109,7 @@
 ; BACKEND2-NEXT: </MODULE_STRTAB_BLOCK
 ; BACKEND2-NEXT: <GLOBALVAL_SUMMARY_BLOCK
 ; BACKEND2-NEXT: <VERSION
+; BACKEND2-NEXT: <FLAGS
 ; BACKEND2-NEXT: <VALUE_GUID op0=1 op1=-5300342847281564238
 ; BACKEND2-NEXT: <COMBINED
 ; BACKEND2-NEXT: </GLOBALVAL_SUMMARY_BLOCK
@@ -118,6 +120,7 @@
 ; COMBINED-NEXT: </MODULE_STRTAB_BLOCK
 ; COMBINED-NEXT: <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT: <VERSION
+; COMBINED-NEXT: <FLAGS
 ; COMBINED-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
 ; COMBINED-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
 ; COMBINED-NEXT: <COMBINED
diff --git a/llvm/test/tools/llvm-lto/thinlto.ll b/llvm/test/tools/llvm-lto/thinlto.ll
index 86aca13a4c8..23843e07d6a 100644
--- a/llvm/test/tools/llvm-lto/thinlto.ll
+++ b/llvm/test/tools/llvm-lto/thinlto.ll
@@ -11,6 +11,7 @@
 ; COMBINED-NEXT: </MODULE_STRTAB_BLOCK
 ; COMBINED-NEXT: <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT: <VERSION
+; COMBINED-NEXT: <FLAGS
 ; COMBINED-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
 ; COMBINED-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
 ; COMBINED-NEXT: <COMBINED
diff --git a/llvm/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp b/llvm/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
index fd673701943..857e0486b96 100644
--- a/llvm/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
+++ b/llvm/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
@@ -315,6 +315,7 @@ static const char *GetCodeName(unsigned CodeID, unsigned BlockID,
       STRINGIFY_CODE(FS, COMBINED_ALIAS)
       STRINGIFY_CODE(FS, COMBINED_ORIGINAL_NAME)
       STRINGIFY_CODE(FS, VERSION)
+      STRINGIFY_CODE(FS, FLAGS)
       STRINGIFY_CODE(FS, TYPE_TESTS)
       STRINGIFY_CODE(FS, TYPE_TEST_ASSUME_VCALLS)
       STRINGIFY_CODE(FS, TYPE_CHECKED_LOAD_VCALLS)