[llvm] r227431 - Don't create multiple mergeable sections with -fdata-sections.

[Rafael Espindola]

Author: rafael
Date: Thu Jan 29 06:43:28 2015
New Revision: 227431

URL: http://llvm.org/viewvc/llvm-project?rev=227431&view=rev
Log:
Don't create multiple mergeable sections with -fdata-sections.

ELF has support for sections that can be split into fixed size or
null terminated entities.

Since these sections can be split by the linker, it is not necessary
to split them in codegen.

This reduces the combined .o size in a llvm+clang build from
202,394,570 to 173,819,098 bytes.

The time for linking clang with gold (on a VM, on a laptop) goes
from 2.250089985 to 1.383001792 seconds.

The flip side is the size of rodata in clang goes from 10,926,785
to 10,929,345 bytes.

The increase seems to be because of http://sourceware.org/bugzilla/show_bug.cgi?id=17902.

Modified:
    llvm/trunk/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
    llvm/trunk/test/CodeGen/X86/global-sections.ll

Modified: llvm/trunk/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/TargetLoweringObjectFileImpl.cpp?rev=227431&r1=227430&r2=227431&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (original)
+++ llvm/trunk/lib/CodeGen/TargetLoweringObjectFileImpl.cpp Thu Jan 29 06:43:28 2015
@@ -246,24 +246,25 @@ static StringRef getSectionPrefixForGlob
 const MCSection *TargetLoweringObjectFileELF::
 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
                        Mangler &Mang, const TargetMachine &TM) const {
+  unsigned Flags = getELFSectionFlags(Kind);
+
   // If we have -ffunction-section or -fdata-section then we should emit the
   // global value to a uniqued section specifically for it.
-  bool EmitUniquedSection;
-  if (Kind.isText())
-    EmitUniquedSection = TM.getFunctionSections();
-  else
-    EmitUniquedSection = TM.getDataSections();
+  bool EmitUniquedSection = false;
+  if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
+    if (Kind.isText())
+      EmitUniquedSection = TM.getFunctionSections();
+    else
+      EmitUniquedSection = TM.getDataSections();
+  }
 
-  // If this global is linkonce/weak and the target handles this by emitting it
-  // into a 'uniqued' section name, create and return the section now.
-  if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
+  if (EmitUniquedSection || GV->hasComdat()) {
     StringRef Prefix = getSectionPrefixForGlobal(Kind);
 
     SmallString<128> Name(Prefix);
     TM.getNameWithPrefix(Name, GV, Mang, true);
 
     StringRef Group = "";
-    unsigned Flags = getELFSectionFlags(Kind);
     if (const Comdat *C = getELFComdat(GV)) {
       Flags |= ELF::SHF_GROUP;
       Group = C->getName();

Modified: llvm/trunk/test/CodeGen/X86/global-sections.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/global-sections.ll?rev=227431&r1=227430&r2=227431&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/global-sections.ll (original)
+++ llvm/trunk/test/CodeGen/X86/global-sections.ll Thu Jan 29 06:43:28 2015
@@ -121,7 +121,7 @@ define void @F1() {
 ; LINUX: G7:
 ; LINUX:        .asciz  "abcdefghi"
 
-; LINUX-SECTIONS: .section        .rodata.G7,"aMS", at progbits,1
+; LINUX-SECTIONS: .section        .rodata.str1.1,"aMS", at progbits,1
 ; LINUX-SECTIONS:       .globl G7
 
 ; WIN32-SECTIONS: .section        .rdata,"rd",one_only,_G7
@@ -182,7 +182,7 @@ define void @F1() {
 @G14 = private unnamed_addr constant [4 x i8] c"foo\00", align 1
 
 ; LINUX-SECTIONS:        .type   .LG14, at object           # @G14
-; LINUX-SECTIONS:        .section        .rodata..LG14,"aMS", at progbits,1
+; LINUX-SECTIONS:        .section        .rodata.str1.1,"aMS", at progbits,1
 ; LINUX-SECTIONS: .LG14:
 ; LINUX-SECTIONS:        .asciz  "foo"
 ; LINUX-SECTIONS:        .size   .LG14, 4
@@ -206,7 +206,7 @@ define void @F1() {
 ; DARWIN64: .section       __TEXT,__const
 ; DARWIN64: _G15:
 
-; LINUX-SECTIONS: .section      .rodata.G15,"aM", at progbits,8
+; LINUX-SECTIONS: .section      .rodata.cst8,"aM", at progbits,8
 ; LINUX-SECTIONS: G15:
 
 ; WIN32-SECTIONS: .section      .rdata,"rd",one_only,_G15