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[COFF] Enable per-function and data sections in LTO
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Authored by rnk on Mar 14 2018, 1:12 PM.

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Summary

This allows post-LTO symbol reordering and ICF.

Build Status

Buildable 16086
Build 16086: arc lint + arc unit

lgtm, we do the same exact thing in ELF, I don't see why COFF should be different.

This revision is now accepted and ready to land.Mar 14 2018, 1:15 PM

LGTM

This revision was automatically updated to reflect the committed changes.

Path

Size

lld/

COFF/

6 lines

test/

COFF/

26 lines

Show First 20 Lines • Show All 58 Lines • ▼ Show 20 Lines	static void saveBuffer(StringRef Buffer, const Twine &Path) {
if (EC)		if (EC)
error("cannot create " + Path + ": " + EC.message());		error("cannot create " + Path + ": " + EC.message());
OS << Buffer;		OS << Buffer;
}		}

static std::unique_ptr<lto::LTO> createLTO() {		static std::unique_ptr<lto::LTO> createLTO() {
lto::Config Conf;		lto::Config Conf;
Conf.Options = InitTargetOptionsFromCodeGenFlags();		Conf.Options = InitTargetOptionsFromCodeGenFlags();

		// Always emit a section per function/datum with LTO. LLVM LTO should get most
		// of the benefit of linker GC, but there are still opportunities for ICF.
		Conf.Options.FunctionSections = true;
		Conf.Options.DataSections = true;

// Use static reloc model on 32-bit x86 because it usually results in more		// Use static reloc model on 32-bit x86 because it usually results in more
// compact code, and because there are also known code generation bugs when		// compact code, and because there are also known code generation bugs when
// using the PIC model (see PR34306).		// using the PIC model (see PR34306).
if (Config->Machine == COFF::IMAGE_FILE_MACHINE_I386)		if (Config->Machine == COFF::IMAGE_FILE_MACHINE_I386)
Conf.RelocModel = Reloc::Static;		Conf.RelocModel = Reloc::Static;
else		else
Conf.RelocModel = Reloc::PIC_;		Conf.RelocModel = Reloc::PIC_;
Conf.DisableVerify = true;		Conf.DisableVerify = true;
▲ Show 20 Lines • Show All 89 Lines • Show Last 20 Lines

				; Test that ICF works after LTO, i.e. both functions have the same address.
				; Previously, when we didn't enable function sections, ICF didn't work.

				; RUN: llvm-as %s -o %t.bc
				; RUN: lld-link -opt:icf -dll -noentry %t.bc -out:%t.dll
				; RUN: llvm-readobj -coff-exports %t.dll \| FileCheck %s

				; CHECK: Export {
				; CHECK: Export {
				; CHECK: RVA: 0x[[RVA:.*]]
				; CHECK: Export {
				; CHECK: RVA: 0x[[RVA]]
				; CHECK-NOT: Export

				target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
				target triple = "x86_64-pc-windows-msvc19.12.25835"

				define dllexport i8* @icf_ptr() {
				entry:
				ret i8* null
				}

				define dllexport i64 @icf_int() {
				entry:
				ret i64 0
				}