[BOLT] Add fuzzy function name matching for LLVM LTO

[maksfb]

Summary

LLVM with LTO can generate function names in the form
func.llvm.<number>, where <number> could vary based on the compilation
environment. As a result, if a profiled binary originated from a
different build than a corresponding binary used for BOLT optimization,
then profiles for such LTO functions will be ignored.

To fix the problem, use "fuzzy" matching with "func.llvm.*" form.

[Amir]

LG

BTW: is there any way to trigger these suffixes from source level test?

[maksfb]

Make the test more resilient to the system compiler/linker variations.

[maksfb]

In D124117#3462912, @Amir wrote:

BTW: is there any way to trigger these suffixes from source level test?

There might be, but that would be way more involved and dependent on the compiler code gen.

bolt/lib/Profile/DataReader.cpp

 namespace bolt {
 
 Optional<StringRef> getLTOCommonName(const StringRef Name) {
   size_t LTOSuffixPos = Name.find(".lto_priv.");
   if (LTOSuffixPos != StringRef::npos)
     return Name.substr(0, LTOSuffixPos + 10);
   if ((LTOSuffixPos = Name.find(".constprop.")) != StringRef::npos)
     return Name.substr(0, LTOSuffixPos + 11);
+  if ((LTOSuffixPos = Name.find(".llvm.")) != StringRef::npos)
+    return Name.substr(0, LTOSuffixPos + 6);
   return NoneType();
 }
 
 namespace {
 
 /// Return true if the function name can change across compilations.
 bool hasVolatileName(const BinaryFunction &BF) {
   for (const StringRef Name : BF.getNames())

bolt/test/X86/lto-name-match.s

+# REQUIRES: system-linux
+
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
+# RUN: link_fdata %s %t.o %t.fdata
+# RUN: llvm-strip --strip-unneeded %t.o
+# RUN: %clang %cflags %t.o -o %t.exe
+# RUN: llvm-bolt %t.exe -data %t.fdata -o /dev/null | FileCheck %s
+
+## Check that profile is correctly matched by functions with variable suffixes.
+## E.g., LTO-generated name foo.llvm.123 should match foo.llvm.*.
+
+# CHECK: 4 out of {{.*}} functions in the binary {{.*}} have non-empty execution profile
+# CHECK-NOT: profile for {{.*}} objects was ignored
+
+  .globl _start
+_start:
+
+LL_start_0:
+# FDATA: 1 _start #LL_start_0# 1 foo.llvm.321 0 0 1
+  call foo.llvm.123
+
+LL_start_1:
+# FDATA: 1 _start #LL_start_1# 1 foo.constprop.321 0 0 1
+  call foo.constprop.123
+
+LL_start_2:
+# FDATA: 1 _start #LL_start_2# 1 foo.lto_priv.321 0 0 1
+  call foo.lto_priv.123
+
+  call exit
+  .size _start, .-_start
+
+  .globl foo.llvm.123
+  .type foo.llvm.123,@function
+foo.llvm.123:
+  ret
+  .size foo.llvm.123, .-foo.llvm.123
+
+  .globl foo.constprop.123
+  .type foo.constprop.123,@function
+foo.constprop.123:
+  ret
+  .size foo.constprop.123, .-foo.constprop.123
+
+  .globl foo.lto_priv.123
+  .type foo.lto_priv.123,@function
+foo.lto_priv.123:
+  ret
+  .size foo.lto_priv.123, .-foo.lto_priv.123