New llc option pie-copy-relocations to optimize access to extern globals.

This option indicates copy relocations support is available from the linker
when building as PIE and allows accesses to extern globals to avoid the GOT.

Differential Revision: https://reviews.llvm.org/D24849

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284160 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/MC/MCTargetOptions.h b/include/llvm/MC/MCTargetOptions.h
index fd4c6e4e4fbf0bab5671323937d0a7bf72a12ef9..21091b378f8ff5e44446da9e9278279d3c469743 100644 (file)
--- a/include/llvm/MC/MCTargetOptions.h
+++ b/include/llvm/MC/MCTargetOptions.h
@@ -41,6 +41,7 @@ public:
   bool MCSaveTempLabels : 1;
   bool MCUseDwarfDirectory : 1;
   bool MCIncrementalLinkerCompatible : 1;
+  bool MCPIECopyRelocations : 1;
   bool ShowMCEncoding : 1;
   bool ShowMCInst : 1;
   bool AsmVerbose : 1;
@@ -67,6 +68,7 @@ inline bool operator==(const MCTargetOptions &LHS, const MCTargetOptions &RHS) {
           ARE_EQUAL(MCSaveTempLabels) &&
           ARE_EQUAL(MCUseDwarfDirectory) &&
           ARE_EQUAL(MCIncrementalLinkerCompatible) &&
+          ARE_EQUAL(MCPIECopyRelocations) &&
           ARE_EQUAL(ShowMCEncoding) &&
           ARE_EQUAL(ShowMCInst) &&
           ARE_EQUAL(AsmVerbose) &&

diff --git a/include/llvm/MC/MCTargetOptionsCommandFlags.h b/include/llvm/MC/MCTargetOptionsCommandFlags.h
index 801dd6a2d502dd5b5d5de6dea45228e92c4cd410..cb020845801a4cd81228fc6b1ca0651811ade37f 100644 (file)
--- a/include/llvm/MC/MCTargetOptionsCommandFlags.h
+++ b/include/llvm/MC/MCTargetOptionsCommandFlags.h
@@ -38,6 +38,8 @@ cl::opt<bool> IncrementalLinkerCompatible(
         "When used with filetype=obj, "
         "emit an object file which can be used with an incremental linker"));
 
+cl::opt<bool> PIECopyRelocations("pie-copy-relocations", cl::desc("PIE Copy Relocations"));
+
 cl::opt<int> DwarfVersion("dwarf-version", cl::desc("Dwarf version"),
                           cl::init(0));
 
@@ -62,6 +64,7 @@ static inline MCTargetOptions InitMCTargetOptionsFromFlags() {
       (AsmInstrumentation == MCTargetOptions::AsmInstrumentationAddress);
   Options.MCRelaxAll = RelaxAll;
   Options.MCIncrementalLinkerCompatible = IncrementalLinkerCompatible;
+  Options.MCPIECopyRelocations = PIECopyRelocations;
   Options.DwarfVersion = DwarfVersion;
   Options.ShowMCInst = ShowMCInst;
   Options.ABIName = ABIName;

diff --git a/lib/MC/MCTargetOptions.cpp b/lib/MC/MCTargetOptions.cpp
index 1d956a8ffceb2b4b0e5362857bd303f9f741a2e4..e847a17dfec5dbc73c7a07dd745b985eb4519a88 100644 (file)
--- a/lib/MC/MCTargetOptions.cpp
+++ b/lib/MC/MCTargetOptions.cpp
@@ -16,7 +16,8 @@ MCTargetOptions::MCTargetOptions()
     : SanitizeAddress(false), MCRelaxAll(false), MCNoExecStack(false),
       MCFatalWarnings(false), MCNoWarn(false), MCSaveTempLabels(false),
       MCUseDwarfDirectory(false), MCIncrementalLinkerCompatible(false),
-      ShowMCEncoding(false), ShowMCInst(false), AsmVerbose(false),
+      MCPIECopyRelocations(false), ShowMCEncoding(false),
+      ShowMCInst(false), AsmVerbose(false),
       PreserveAsmComments(true), DwarfVersion(0), ABIName() {}
 
 StringRef MCTargetOptions::getABIName() const {

diff --git a/lib/Target/TargetMachine.cpp b/lib/Target/TargetMachine.cpp
index 43a587ba847bf6c2fe7200e78bd1094881f44898..792280af84dd2e7f4a20e0ccd6d1e3ababab1290 100644 (file)
--- a/lib/Target/TargetMachine.cpp
+++ b/lib/Target/TargetMachine.cpp
@@ -115,9 +115,6 @@ static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
   llvm_unreachable("invalid TLS model");
 }
 
-// FIXME: make this a proper option
-static bool CanUseCopyRelocWithPIE = false;
-
 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
                                          const GlobalValue *GV) const {
   Reloc::Model RM = getRelocationModel();
@@ -154,8 +151,10 @@ bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
       return true;
 
     bool IsTLS = GV && GV->isThreadLocal();
+    bool IsAccessViaCopyRelocs =
+        Options.MCOptions.MCPIECopyRelocations && GV && isa<GlobalVariable>(GV);
     // Check if we can use copy relocations.
-    if (!IsTLS && (RM == Reloc::Static || CanUseCopyRelocWithPIE))
+    if (!IsTLS && (RM == Reloc::Static || IsAccessViaCopyRelocs))
       return true;
   }
 

diff --git a/test/CodeGen/X86/global-access-pie-copyrelocs.ll b/test/CodeGen/X86/global-access-pie-copyrelocs.ll
new file mode 100644 (file)
index 0000000..5c4a87c
--- /dev/null
+++ b/test/CodeGen/X86/global-access-pie-copyrelocs.ll
@@ -0,0 +1,119 @@
+; RUN: llc < %s -march=x86-64 -mcpu=generic -mtriple=x86_64-linux-gnu -relocation-model=pic -pie-copy-relocations \
+; RUN:   | FileCheck -check-prefix=X64 %s
+; RUN: llc < %s -emulated-tls -march=x86 -mcpu=generic -mtriple=i386-linux-gnu -relocation-model=pic -pie-copy-relocations \
+; RUN:   | FileCheck -check-prefix=X32 %s
+
+; External Linkage
+@a = global i32 0, align 4
+
+define i32 @my_access_global_a() #0 {
+; X32-LABEL: my_access_global_a:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32-NEXT:  movl a@GOTOFF(%eax), %eax
+; X64-LABEL: my_access_global_a:
+; X64:       movl a(%rip), %eax
+
+entry:
+  %0 = load i32, i32* @a, align 4
+  ret i32 %0
+}
+
+; WeakAny Linkage
+@b = weak global i32 0, align 4
+
+define i32 @my_access_global_b() #0 {
+; X32-LABEL: my_access_global_b:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32-NEXT:  movl b@GOTOFF(%eax), %eax
+; X64-LABEL: my_access_global_b:
+; X64:       movl b(%rip), %eax
+
+entry:
+  %0 = load i32, i32* @b, align 4
+  ret i32 %0
+}
+
+; Internal Linkage
+@c = internal global i32 0, align 4
+
+define i32 @my_access_global_c() #0 {
+; X32-LABEL: my_access_global_c:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32-NEXT:  movl c@GOTOFF(%eax), %eax
+; X64-LABEL: my_access_global_c:
+; X64:       movl c(%rip), %eax
+
+entry:
+  %0 = load i32, i32* @c, align 4
+  ret i32 %0
+}
+
+; External Linkage, only declaration.
+@d = external global i32, align 4
+
+define i32 @my_access_global_load_d() #0 {
+; X32-LABEL: my_access_global_load_d:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32-NEXT:  movl d@GOTOFF(%eax), %eax
+; X64-LABEL: my_access_global_load_d:
+; X64:       movl d(%rip), %eax
+
+entry:
+  %0 = load i32, i32* @d, align 4
+  ret i32 %0
+}
+
+; External Linkage, only declaration, store a value.
+
+define i32 @my_access_global_store_d() #0 {
+; X32-LABEL: my_access_global_store_d:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32-NEXT:  movl $2, d@GOTOFF(%eax)
+; X64-LABEL: my_access_global_store_d:
+; X64:  movl $2, d(%rip)
+
+entry:
+  store i32 2, i32* @d, align 4
+  ret i32 0
+}
+
+; External Linkage, function pointer access.
+declare i32 @access_fp(i32 ()*)
+declare i32 @foo()
+
+define i32 @my_access_fp_foo() #0 {
+; X32-LABEL: my_access_fp_foo:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %ebx
+; X32-NEXT:  movl      foo@GOT(%ebx), %eax
+; X64-LABEL: my_access_fp_foo:
+; X64:       movq foo@GOTPCREL(%rip), %rdi
+
+entry:
+  %call = call i32 @access_fp(i32 ()* @foo)
+  ret i32 %call
+}
+
+; LinkOnceODR Linkage, function pointer access.
+
+$bar = comdat any
+
+define linkonce_odr i32 @bar() comdat {
+entry:
+  ret i32 0
+}
+
+define i32 @my_access_fp_bar() #0 {
+; X32-LABEL: my_access_fp_bar:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %ebx
+; X32-NEXT:  leal      bar@GOTOFF(%ebx), %eax
+; X64-LABEL: my_access_fp_bar:
+; X64:       leaq bar(%rip), %rdi
+
+entry:
+  %call = call i32 @access_fp(i32 ()* @bar)
+  ret i32 %call
+}
+
+!llvm.module.flags = !{!0, !1}
+!0 = !{i32 1, !"PIC Level", i32 1}
+!1 = !{i32 1, !"PIE Level", i32 1}