lld: Reduce number of references to undefined printed from 10 to 3.

[thakis]

Summary

As of a while ago, lld groups all undefined references to a single
symbol in a single diagnostic. Back then, I made it so that we
print up to 10 references to each undefined symbol.

Having used this for a while, I never wished there were more
references, but I sometimes found that this can print a lot of
output. lld prints up to 10 diagnostics by default, and if
each has 10 references (which I've seen in practice), and each
undefined symbol produces 2 (possibly very long) lines of output,
that's over 200 lines of error output.

Let's try it with just 3 references for a while and see how
that feels in practice.

[thakis]

(If someone wants to see _all_ undefined refs, we could make it so that -ferror-limit=0 disables this limiting, but I haven't heard anyone wishing for that so far, so I wouldn't do that for now.)

[MaskRay]

In D77017#1948650, @thakis wrote:

(If someone wants to see _all_ undefined refs, we could make it so that -ferror-limit=0 disables this limiting, but I haven't heard anyone wishing for that so far, so I wouldn't do that for now.)

I assume you mean --error-limit=0. Yeah, I don't know who has a need for that so far.

[MaskRay]

LGTM.

[thakis]

Thanks! Landed in 20eb719f99c4979838c2995a447452f9fc3d3605.

lld/COFF/SymbolTable.cpp

struct UndefinedDiag {
   std::vector<File> files;
 };
 
 static void reportUndefinedSymbol(const UndefinedDiag &undefDiag) {
   std::string out;
   llvm::raw_string_ostream os(out);
   os << "undefined symbol: " << toString(*undefDiag.sym);
 
-  const size_t maxUndefReferences = 10;
+  const size_t maxUndefReferences = 3;
   size_t i = 0, numRefs = 0;
   for (const UndefinedDiag::File &ref : undefDiag.files) {
     std::vector<std::string> symbolLocations =
         getSymbolLocations(ref.file, ref.symIndex);
     numRefs += symbolLocations.size();
     for (const std::string &s : symbolLocations) {
       if (i >= maxUndefReferences)
         break;

lld/ELF/Relocations.cpp

default:
       return "";
     }
   };
 
   std::string msg = maybeReportDiscarded<ELFT>(cast<Undefined>(sym));
   if (msg.empty())
     msg = "undefined " + visibility() + "symbol: " + toString(sym);
 
-  const size_t maxUndefReferences = 10;
+  const size_t maxUndefReferences = 3;
   size_t i = 0;
   for (UndefinedDiag::Loc l : undef.locs) {
     if (i >= maxUndefReferences)
       break;
     InputSectionBase &sec = *l.sec;
     uint64_t offset = l.offset;
 
     msg += "\n>>> referenced by ";

lld/test/COFF/undefined-symbol-multi.s

 # RUN: echo '  call "?foo@@YAHXZ"' >> %t.moreref.s
 # RUN: llvm-mc -triple=x86_64-windows-msvc -filetype=obj -o %t2.obj %t.moreref.s
 # RUN: not lld-link /out:/dev/null  %t.obj %t2.obj 2>&1 | FileCheck %s
 
 # CHECK: error: undefined symbol: int __cdecl foo(void)
 # CHECK-NEXT: >>> referenced by {{.*}}tmp.obj:(main)
 # CHECK-NEXT: >>> referenced by {{.*}}tmp.obj:(main)
 # CHECK-NEXT: >>> referenced by {{.*}}tmp2.obj:(bar)
-# CHECK-NEXT: >>> referenced by {{.*}}tmp2.obj:(bar)
-# CHECK-NEXT: >>> referenced by {{.*}}tmp2.obj:(bar)
-# CHECK-NEXT: >>> referenced by {{.*}}tmp2.obj:(bar)
-# CHECK-NEXT: >>> referenced by {{.*}}tmp2.obj:(bar)
-# CHECK-NEXT: >>> referenced by {{.*}}tmp2.obj:(bar)
-# CHECK-NEXT: >>> referenced by {{.*}}tmp2.obj:(bar)
-# CHECK-NEXT: >>> referenced by {{.*}}tmp2.obj:(bar)
-# CHECK-NEXT: >>> referenced 2 more times
+# CHECK-NEXT: >>> referenced 9 more times
 # CHECK-EMPTY:
 # CHECK-NEXT: error: undefined symbol: int __cdecl bar(void)
 # CHECK-NEXT: >>> referenced by {{.*}}.obj:(main)
 # CHECK-NEXT: >>> referenced by {{.*}}.obj:(f1)
 
         .section        .text,"xr",one_only,main
 .globl main
 main:
   call  "?foo@@YAHXZ"
   call  "?foo@@YAHXZ"
   call  "?bar@@YAHXZ"
 
 f1:
   call  "?bar@@YAHXZ"
 .Lfunc_end1:

lld/test/ELF/undef-multi.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/undef.s -o %t2.o
 # RUN: not ld.lld %t.o %t2.o -o /dev/null 2>&1 | FileCheck %s
 
 # CHECK: error: undefined symbol: zed2
 # CHECK-NEXT: >>> referenced by undef-multi.s
 # CHECK-NEXT: >>>               {{.*}}:(.text+0x1)
 # CHECK-NEXT: >>> referenced by undef-multi.s
 # CHECK-NEXT: >>>               {{.*}}:(.text+0x6)
 # CHECK-NEXT: >>> referenced by undef-multi.s
 # CHECK-NEXT: >>>               {{.*}}:(.text+0xB)
-# CHECK-NEXT: >>> referenced by undef-multi.s
-# CHECK-NEXT: >>>               {{.*}}:(.text+0x10)
-# CHECK-NEXT: >>> referenced by {{.*}}tmp2.o:(.text+0x0)
+# CHECK-NEXT: >>> referenced 2 more times
 
 # All references to a single undefined symbol count as a single error -- but
 # at most 10 references are printed.
 # RUN: echo ".globl _bar" > %t.moreref.s
 # RUN: echo "_bar:" >> %t.moreref.s
 # RUN: echo "  call zed2" >> %t.moreref.s
 # RUN: echo "  call zed2" >> %t.moreref.s
 # RUN: echo "  call zed2" >> %t.moreref.s
 # RUN: echo "  call zed2" >> %t.moreref.s
 # RUN: echo "  call zed2" >> %t.moreref.s
 # RUN: echo "  call zed2" >> %t.moreref.s
 # RUN: echo "  call zed2" >> %t.moreref.s
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %t.moreref.s -o %t3.o
 # RUN: not ld.lld %t.o %t2.o %t3.o -o /dev/null -error-limit=2 2>&1 | \
 # RUN:     FileCheck --check-prefix=LIMIT %s
 
 # LIMIT: error: undefined symbol: zed2
 # LIMIT-NEXT: >>> referenced by undef-multi.s
 # LIMIT-NEXT: >>>               {{.*}}:(.text+0x1)
 # LIMIT-NEXT: >>> referenced by undef-multi.s
 # LIMIT-NEXT: >>>               {{.*}}:(.text+0x6)
 # LIMIT-NEXT: >>> referenced by undef-multi.s
 # LIMIT-NEXT: >>>               {{.*}}:(.text+0xB)
-# LIMIT-NEXT: >>> referenced by undef-multi.s
-# LIMIT-NEXT: >>>               {{.*}}:(.text+0x10)
-# LIMIT-NEXT: >>> referenced by {{.*}}tmp2.o:(.text+0x0)
-# LIMIT-NEXT: >>> referenced by {{.*}}tmp3.o:(.text+0x1)
-# LIMIT-NEXT: >>> referenced by {{.*}}tmp3.o:(.text+0x6)
-# LIMIT-NEXT: >>> referenced by {{.*}}tmp3.o:(.text+0xB)
-# LIMIT-NEXT: >>> referenced by {{.*}}tmp3.o:(.text+0x10)
-# LIMIT-NEXT: >>> referenced by {{.*}}tmp3.o:(.text+0x15)
-# LIMIT-NEXT: >>> referenced 2 more times
+# LIMIT-NEXT: >>> referenced 9 more times
 
 .file "undef-multi.s"
 
   .globl _start
 _start:
   call zed2
 
   .globl _f