Don't warn on ICFed symbols, warn on synthetic ones

[• espindola]

Summary

This is based on the idea of https://reviews.llvm.org/D44214 but doesn't include any refactoring.

[ruiu]

LGTM

[• espindola]

r329757

ELF/Writer.cpp

if (Config->WarnSymbolOrdering) {
         warn(toString(File) +
              ": unable to order undefined symbol: " + Sym.getName());
       else if (Sym.isShared())
         warn(toString(File) +
              ": unable to order shared symbol: " + Sym.getName());
       else if (D && !D->Section)
         warn(toString(File) +
              ": unable to order absolute symbol: " + Sym.getName());
-      else if (D && !D->Section->Live)
+      else if (D && isa<OutputSection>(D->Section))
+        warn(toString(File) +
+             ": unable to order synthetic symbol: " + Sym.getName());
+      else if (D && !D->Section->Repl->Live)
         warn(toString(File) +
              ": unable to order discarded symbol: " + Sym.getName());
     }
 
     if (auto *D = dyn_cast<Defined>(&Sym)) {
       if (auto *Sec = dyn_cast_or_null<InputSectionBase>(D->Section)) {
         int &Priority = SectionOrder[cast<InputSectionBase>(Sec->Repl)];
         Priority = std::min(Priority, Ent.Priority);

test/ELF/symbol-ordering-file-warnings.s

 # RUN: ld.lld %t1.o -o %t --symbol-ordering-file %t-order-absolute.txt \
 # RUN:   --unresolved-symbols=ignore-all 2>&1 | FileCheck %s --check-prefixes=WARN,ABSOLUTE
 
 # Check that a warning is emitted for symbols discarded due to --gc-sections.
 # RUN: echo "gc" > %t-order-gc.txt
 # RUN: ld.lld %t1.o -o %t --symbol-ordering-file %t-order-gc.txt --gc-sections \
 # RUN:   --unresolved-symbols=ignore-all 2>&1 | FileCheck %s --check-prefixes=WARN,GC
 
-# Check that a warning is emitted for the symbol removed due to --icf.
+# Check that a warning is not emitted for the symbol removed due to --icf.
 # RUN: echo "icf1" > %t-order-icf.txt
 # RUN: echo "icf2" >> %t-order-icf.txt
 # RUN: ld.lld %t1.o -o %t --symbol-ordering-file %t-order-icf.txt --icf=all \
-# RUN:   --unresolved-symbols=ignore-all 2>&1 | FileCheck %s --check-prefixes=WARN,ICF
+# RUN:   --unresolved-symbols=ignore-all --fatal-warnings
+
+# RUN: echo "_GLOBAL_OFFSET_TABLE_" > %t-order-synthetic.txt
+# RUN: ld.lld %t1.o -o %t --symbol-ordering-file %t-order-synthetic.txt --icf=all \
+# RUN:   --unresolved-symbols=ignore-all 2>&1 | FileCheck %s --check-prefixes=WARN,SYNTHETIC
 
 # Check that a warning is emitted for symbols discarded due to a linker script /DISCARD/ section.
 # RUN: echo "discard" > %t-order-discard.txt
 # RUN: echo "SECTIONS { /DISCARD/ : { *(.text.discard) } }" > %t.script
 # RUN: ld.lld %t1.o -o %t --symbol-ordering-file %t-order-discard.txt -T %t.script \
 # RUN:   --unresolved-symbols=ignore-all 2>&1 | FileCheck %s --check-prefixes=WARN,DISCARD
 
 # Check that LLD does not warn for discarded COMDAT symbols, if they are present in the kept instance.

 # Check that all warnings can be emitted from the same input.
 # RUN: echo "missing_sym" > %t-order-multi.txt
 # RUN: echo "undefined" >> %t-order-multi.txt
 # RUN: echo "_start" >> %t-order-multi.txt
 # RUN: echo "shared" >> %t-order-multi.txt
 # RUN: echo "absolute" >> %t-order-multi.txt
 # RUN: echo "gc" >> %t-order-multi.txt
 # RUN: echo "discard" >> %t-order-multi.txt
+# RUN: echo "_GLOBAL_OFFSET_TABLE_" >> %t-order-multi.txt
 # RUN: echo "_start" >> %t-order-multi.txt
 # RUN: ld.lld %t1.o %t3.o %t.so -o %t --symbol-ordering-file %t-order-multi.txt --gc-sections -T %t.script \
-# RUN:   --unresolved-symbols=ignore-all 2>&1 | FileCheck %s --check-prefixes=WARN,SAMESYM,ABSOLUTE,SHARED,UNDEFINED,GC,DISCARD,MISSING2
+# RUN:   --unresolved-symbols=ignore-all 2>&1 | FileCheck %s --check-prefixes=WARN,SAMESYM,ABSOLUTE,SHARED,UNDEFINED,GC,DISCARD,MISSING2,SYNTHETIC
 
 # WARN-NOT:    warning:
 # SAMESYM:     warning: {{.*}}.txt: duplicate ordered symbol: _start
 # WARN-NOT:    warning:
+# SYNTHETIC:   warning: <internal>: unable to order synthetic symbol: _GLOBAL_OFFSET_TABLE_
+# WARN-NOT:    warning:
 # DISCARD:     warning: {{.*}}1.o: unable to order discarded symbol: discard
 # WARN-NOT:    warning:
 # GC:          warning: {{.*}}1.o: unable to order discarded symbol: gc
 # WARN-NOT:    warning:
 # SHARED:      warning: {{.*}}.so: unable to order shared symbol: shared
 # WARN-NOT:    warning:
 # UNDEFINED:   warning: {{.*}}3.o: unable to order undefined symbol: undefined
 # WARN-NOT:    warning:
 # ABSOLUTE:    warning: {{.*}}1.o: unable to order absolute symbol: absolute
 # WARN-NOT:    warning:
 # MISSING:     warning: symbol ordering file: no such symbol: missing
 # MISSING2:    warning: symbol ordering file: no such symbol: missing_sym
-# ICF:         warning: {{.*}}1.o: unable to order discarded symbol: icf2
 # COMDAT:      warning: {{.*}}1.o: unable to order discarded symbol: comdat
 # MULTI:       warning: {{.*}}3.o: unable to order undefined symbol: multi
 # MULTI-NEXT:  warning: {{.*}}2.o: unable to order absolute symbol: multi
 # WARN-NOT:    warning:
 
 absolute = 0x1234
 
 .section .text.gc,"ax",@progbits

 .section .text.icf2,"ax",@progbits
 .global icf2
 icf2:
     ret
 
 # This is a "good" instance of the symbol
 .section .text.multi,"ax",@progbits
 multi:
-  nop
+  .quad _GLOBAL_OFFSET_TABLE_