[PGO][GlobalValue][LTO]In GlobalValues::getGlobalIdentifier, use semicolon as delimiter for local-linkage varibles. (#74008)

Commit fe05193 (phab D156569), IRPGO names uses format
`[<filepath>;]<linkage-name>` while prior format is
`[<filepath>:<mangled-name>`. The format change would break the use case
demonstrated in (updated)
`llvm/test/Transforms/PGOProfile/thinlto_indirect_call_promotion.ll` and
`compiler-rt/test/profile/instrprof-thinlto-indirect-call-promotion.cpp`

This patch changes `GlobalValues::getGlobalIdentifer` to use the
semicolon.

To elaborate on the scenario how things break without this PR
1. IRPGO raw profiles stores (compressed) IRPGO names of functions in
one section, and per-function profile data in another section. The
[NameRef](https://github.com/llvm/llvm-project/blob/fc715e4cd942612a091097339841733757b53824/compiler-rt/include/profile/InstrProfData.inc#L72)
field in per-function profile data is the MD5 hash of IRPGO names.
2. When raw profiles are converted to indexed format profiles, the
profiled address is
[mapped](https://github.com/llvm/llvm-project/blob/fc715e4cd942612a091097339841733757b53824/llvm/lib/ProfileData/InstrProf.cpp#L876-L885)
to the MD5 hash of the callee.
3. In `pgo-instr-use` thin-lto prelink pipeline, MD5 hash of IRPGO names
will be
[annotated](https://github.com/llvm/llvm-project/blob/fc715e4cd942612a091097339841733757b53824/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp#L1707)
as value profiles, and used to import indirect-call-prom candidates. If
the annotated MD5 hash is computed from the new format while import uses
the prior format, the callee cannot be imported.

*`compiler-rt/test/profile/instrprof-thinlto-indirect-call-promotion.cpp`
is added to have an end-to-end test.
* `llvm/test/Transforms/PGOProfile/thinlto_indirect_call_promotion.ll`
is updated to have better test coverage from another aspect (as runtime
tests are more sensitive to the environment and may be skipped by some
contributors)

1 files changed, 7 insertions, 5 deletions

diff --git a/llvm/lib/IR/Globals.cpp b/llvm/lib/IR/Globals.cpp
index 51bdbeb..239acd2 100644
--- a/llvm/lib/IR/Globals.cpp
+++ b/llvm/lib/IR/Globals.cpp
@@ -144,25 +144,27 @@ void GlobalObject::copyAttributesFrom(const GlobalObject *Src) {
 std::string GlobalValue::getGlobalIdentifier(StringRef Name,
                                              GlobalValue::LinkageTypes Linkage,
                                              StringRef FileName) {
-
   // Value names may be prefixed with a binary '1' to indicate
   // that the backend should not modify the symbols due to any platform
   // naming convention. Do not include that '1' in the PGO profile name.
   if (Name[0] == '\1')
     Name = Name.substr(1);
 
-  std::string NewName = std::string(Name);
+  std::string GlobalName;
   if (llvm::GlobalValue::isLocalLinkage(Linkage)) {
     // For local symbols, prepend the main file name to distinguish them.
     // Do not include the full path in the file name since there's no guarantee
     // that it will stay the same, e.g., if the files are checked out from
     // version control in different locations.
     if (FileName.empty())
-      NewName = NewName.insert(0, "<unknown>:");
+      GlobalName += "<unknown>";
     else
-      NewName = NewName.insert(0, FileName.str() + ":");
+      GlobalName += FileName;
+
+    GlobalName += kGlobalIdentifierDelimiter;
   }
-  return NewName;
+  GlobalName += Name;
+  return GlobalName;
 }
 
 std::string GlobalValue::getGlobalIdentifier() const {