Add 'unifiedlto' option to gold plugin #121336
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Option allows using full LTO when linking bitcode files compiled with unified LTO pipeline.
eleviant
requested review from
mshockwave,
cachemeifyoucan and
teresajohnson
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@llvm/pr-subscribers-lto Author: None (eleviant) ChangesOption allows using full LTO when linking bitcode files compiled with unified LTO pipeline. Full diff: https://github.com/llvm/llvm-project/pull/121336.diff 3 Files Affected:
diff --git a/llvm/test/tools/gold/X86/Inputs/unified-lto-foo.ll b/llvm/test/tools/gold/X86/Inputs/unified-lto-foo.ll
new file mode 100644
index 00000000000000..cd6cb16cd332c4
--- /dev/null
+++ b/llvm/test/tools/gold/X86/Inputs/unified-lto-foo.ll
@@ -0,0 +1,26 @@
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-linux-gnu"
+
+@_g = dso_local local_unnamed_addr global i32 0, align 4
+@llvm.compiler.used = appending global [1 x ptr] [ptr @_g], section "llvm.metadata"
+
+define dso_local i32 @foo(i32 noundef %0) #0 {
+ %2 = add nsw i32 %0, 42
+ store i32 %2, ptr @_g, align 4
+ ret i32 %2
+}
+
+attributes #0 = { noinline }
+
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 1, !"EnableSplitLTOUnit", i32 1}
+!1 = !{i32 1, !"UnifiedLTO", i32 1}
+
+^0 = module: (path: "unified-lto-foo.o", hash: (1995435377, 1643957463, 3737953841, 2630641917, 1043992145))
+^1 = gv: (name: "foo", summaries: (function: (module: ^0, flags: (linkage: external, visibility: default, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), insts: 3, funcFlags: (readNone: 0, readOnly: 0, noRecurse: 1, returnDoesNotAlias: 0, noInline: 1, alwaysInline: 0, noUnwind: 1, mayThrow: 0, hasUnknownCall: 0, mustBeUnreachable: 0), refs: (writeonly ^2)))) ; guid = 6699318081062747564
+^2 = gv: (name: "_g", summaries: (variable: (module: ^0, flags: (linkage: external, visibility: default, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), varFlags: (readonly: 1, writeonly: 1, constant: 0)))) ; guid = 9713702464056781075
+^3 = gv: (name: "llvm.compiler.used", summaries: (variable: (module: ^0, flags: (linkage: appending, visibility: default, notEligibleToImport: 0, live: 1, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 0, writeonly: 0, constant: 0), refs: (^3)))) ; guid = 9610627770985738006
+^4 = flags: 520
+^5 = blockcount: 0
diff --git a/llvm/test/tools/gold/X86/unified-lto.ll b/llvm/test/tools/gold/X86/unified-lto.ll
new file mode 100644
index 00000000000000..cc3e39b4b3b47f
--- /dev/null
+++ b/llvm/test/tools/gold/X86/unified-lto.ll
@@ -0,0 +1,42 @@
+; Check that we can use full LTO with gold plugin when inputs
+; are compiled using unified LTO pipeline
+; RUN: llvm-as %s -o %t.bc
+; RUN: llvm-as %p/Inputs/unified-lto-foo.ll -o %t-foo.bc
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext \
+; RUN: -m elf_x86_64 \
+; RUN: -plugin-opt=unifiedlto \
+; RUN: -plugin-opt=save-temps \
+; RUN: -u main \
+; RUN: %t.bc %t-foo.bc \
+; RUN: -o %t-out
+; RUN: llvm-dis %t-out.0.5.precodegen.bc -o - | FileCheck %s
+
+; Constant propagation is not supported by thin LTO.
+; With full LTO we fold argument into constant 43
+; CHECK: define dso_local noundef i32 @main()
+; CHECK-NEXT: tail call fastcc void @foo()
+; CHECK-NEXT: ret i32 43
+
+; CHECK: define internal fastcc void @foo()
+; CHECK-NEXT: store i32 43, ptr @_g, align 4
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-linux-gnu"
+
+define dso_local i32 @main() {
+ %1 = tail call i32 @foo(i32 noundef 1)
+ ret i32 %1
+}
+
+declare i32 @foo(i32 noundef)
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 1, !"EnableSplitLTOUnit", i32 1}
+!1 = !{i32 1, !"UnifiedLTO", i32 1}
+
+^0 = module: (path: "unified-lto.o", hash: (2850108895, 1189778381, 479678006, 1191715608, 4095117687))
+^1 = gv: (name: "foo") ; guid = 6699318081062747564
+^2 = gv: (name: "main", summaries: (function: (module: ^0, flags: (linkage: external, visibility: default, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), insts: 2, funcFlags: (readNone: 0, readOnly: 0, noRecurse: 0, returnDoesNotAlias: 0, noInline: 0, alwaysInline: 0, noUnwind: 1, mayThrow: 0, hasUnknownCall: 0, mustBeUnreachable: 0), calls: ((callee: ^1, tail: 1))))) ; guid = 15822663052811949562
+^3 = flags: 520
+^4 = blockcount: 0
diff --git a/llvm/tools/gold/gold-plugin.cpp b/llvm/tools/gold/gold-plugin.cpp
index 6d0021c85f20fb..ac2e9d4252aa38 100644
--- a/llvm/tools/gold/gold-plugin.cpp
+++ b/llvm/tools/gold/gold-plugin.cpp
@@ -154,6 +154,8 @@ namespace options {
static std::string extra_library_path;
static std::string triple;
static std::string mcpu;
+ // Tells plugin to use unified lto
+ static bool unifiedlto = false;
// When the thinlto plugin option is specified, only read the function
// the information from intermediate files and write a combined
// global index for the ThinLTO backends.
@@ -248,6 +250,8 @@ namespace options {
TheOutputType = OT_DISABLE;
} else if (opt == "emit-asm") {
TheOutputType = OT_ASM_ONLY;
+ } else if (opt == "unifiedlto") {
+ unifiedlto = true;
} else if (opt == "thinlto") {
thinlto = true;
} else if (opt == "thinlto-index-only") {
@@ -893,6 +897,7 @@ static std::unique_ptr<LTO> createLTO(IndexWriteCallback OnIndexWrite,
Conf.OptLevel = options::OptLevel;
Conf.PTO.LoopVectorization = options::OptLevel > 1;
Conf.PTO.SLPVectorization = options::OptLevel > 1;
+ Conf.PTO.UnifiedLTO = options::unifiedlto;
Conf.AlwaysEmitRegularLTOObj = !options::obj_path.empty();
if (options::thinlto_index_only) {
@@ -972,8 +977,13 @@ static std::unique_ptr<LTO> createLTO(IndexWriteCallback OnIndexWrite,
Conf.TimeTraceEnabled = !options::time_trace_file.empty();
Conf.TimeTraceGranularity = options::time_trace_granularity;
+ LTO::LTOKind ltoKind = LTO::LTOK_Default;
+ if (options::unifiedlto)
+ ltoKind =
+ options::thinlto ? LTO::LTOK_UnifiedThin : LTO::LTOK_UnifiedRegular;
return std::make_unique<LTO>(std::move(Conf), Backend,
- options::ParallelCodeGenParallelismLevel);
+ options::ParallelCodeGenParallelismLevel,
+ ltoKind);
}
// Write empty files that may be expected by a distributed build
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@ormris can you take a look? In particular, I'm confused at how this gets enabled via lld. It appears there isn't a separate unified LTO option there, and the mode is set unconditionally to UnifiedThin or UnifiedRegular based on the llvm-project/lld/ELF/Driver.cpp Lines 1651 to 1662 in c7d2370 But then it looks like in the LTO code we will give an error if modules weren't built with -funified-lto: llvm-project/llvm/lib/LTO/LTO.cpp Lines 768 to 773 in c7d2370 I can't recall how this is this supposed to work? |
I think this shouldn't work. The only reason we don't really observe the issue is that clang is not passing --lto option to the linker. So lld is also "thinlto only" with -funified-lto. |
| @@ -0,0 +1,42 @@ | |||
| ; Check that we can use full LTO with gold plugin when inputs | |||
There was a problem hiding this comment.
Can you add some kind of check that unified LTO inputs works with ThinLTO as well?
Ok, I see. The lld |
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Addressed review comments |
Option allows using full LTO when linking bitcode files compiled with unified LTO pipeline.