[profile] Move __llvm_profile_filename into a separate object

[vsk]

Summary

Users can specify the path a raw profile is written to by passing
-fprofile-instr-generate=<path>, but this functionality broke on Darwin
after __llvm_profile_filename was made weak [1], resulting in profiles
being written to "default.profraw" even when <path> is specified.

The situation is that instrumented programs provide a weak definition of
__llvm_profile_filename, which conflicts with a weak redefinition
provided by the profiling runtime.

The linker appears to pick the 'winning' definition arbitrarily: on
Darwin, it usually prefers the larger definition, which is probably why
the instrprof-override-filename.c test has been passing.

The fix is to move the runtime's definition into a separate object file
within the archive. This means that the linker won't "see" the runtime's
definition unless the user program has not provided one. I couldn't
think of a great way to test this other than to mimic the Darwin
failure: use -fprofile-instr-generate=<some-small-path>.

Testing: check-{clang,profile}, modified instrprof-override-filename.c.

[1] [Profile] deprecate __llvm_profile_override_default_filename
https://reviews.llvm.org/D22613
https://reviews.llvm.org/D22614

[davidxl]

test/profile/instrprof-override-filename.c

1–14

can you add a test for IR PGO too using %clang_pgogen=%t.dir/ ...

[arphaman]

lg from my side, thanks

[vsk]

Address David's review comment. I could not use the exact same test structure for IR PGO due to what seems like a spurious hash mismatch (see the FIXME).

[vsk]

Per David's suggestion, make sure the pipelines for the clang_pgogen/clang_profuse pair match.

[davidxl]

lgtm

lib/profile/CMakeLists.txt

 set(PROFILE_SOURCES
   GCDAProfiling.c
   InstrProfiling.c
   InstrProfilingValue.c
   InstrProfilingBuffer.c
   InstrProfilingFile.c
   InstrProfilingMerge.c
   InstrProfilingMergeFile.c
+  InstrProfilingNameVar.c
   InstrProfilingWriter.c
   InstrProfilingPlatformDarwin.c
   InstrProfilingPlatformLinux.c
   InstrProfilingPlatformOther.c
   InstrProfilingRuntime.cc
   InstrProfilingUtil.c)
 
 if(WIN32)

lib/profile/InstrProfiling.c

 #include <stdlib.h>
 #include <string.h>
 #define INSTR_PROF_VALUE_PROF_DATA
 #include "InstrProfData.inc"
 
 
 COMPILER_RT_WEAK uint64_t INSTR_PROF_RAW_VERSION_VAR = INSTR_PROF_RAW_VERSION;
 
-COMPILER_RT_WEAK char INSTR_PROF_PROFILE_NAME_VAR[1] = {0};
-
 COMPILER_RT_VISIBILITY uint64_t __llvm_profile_get_magic(void) {
   return sizeof(void *) == sizeof(uint64_t) ? (INSTR_PROF_RAW_MAGIC_64)
                                             : (INSTR_PROF_RAW_MAGIC_32);
 }
 
 static unsigned ProfileDumped = 0;
 
 COMPILER_RT_VISIBILITY unsigned lprofProfileDumped() {

lib/profile/InstrProfilingNameVar.c

+//===- InstrProfilingNameVar.c - profile name variable setup --------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "InstrProfiling.h"
+
+/* char __llvm_profile_filename[1]
+ *
+ * The runtime should only provide its own definition of this symbol when the
+ * user has not specified one. Set this up by moving the runtime's copy of this
+ * symbol to an object file within the archive.
+ */
+COMPILER_RT_WEAK char INSTR_PROF_PROFILE_NAME_VAR[1] = {0};

test/profile/instrprof-override-filename.c

-// RUN: %clang_profgen=%t.profraw -o %t -O3 %s
-// RUN: %run %t %t.profraw
-// RUN: llvm-profdata merge -o %t.profdata %t.profraw
-// RUN: %clang_profuse=%t.profdata -o - -S -emit-llvm %s | FileCheck %s
+// RUN: rm -rf %t.dir && mkdir -p %t.dir
+// RUN: cd %t.dir
+//
+// RUN: %clang_profgen=P_RAW -o %t -O3 %s
+// RUN: %run %t P_RAW
+// RUN: llvm-profdata merge -o %t.profdata P_RAW
+// RUN: %clang_profuse=%t.profdata -o - -S -emit-llvm %s | FileCheck %s --check-prefix=FE
+//
+// RUN: %clang_pgogen=I_RAW -o %t.2 -O3 %s
+// RUN: %run %t.2 I_RAW
+// RUN: llvm-profdata merge -o %t2.profdata I_RAW
+//
+// FIXME: IRPGO states that there is a hash mismatch in main, and does not produce
+// branch weight metadata: %clang_profuse=%t2.profdata -o - -S -emit-llvm %s 
 
 void bar() {}
 int main(int argc, const char *argv[]) {
-  // CHECK: br i1 %{{.*}}, label %{{.*}}, label %{{.*}}, !prof ![[PD1:[0-9]+]]
+  // FE: br i1 %{{.*}}, label %{{.*}}, label %{{.*}}, !prof ![[PD1:[0-9]+]]
   if (argc < 2)
     return 1;
   bar();
   return 0;
 }
-// CHECK: ![[PD1]] = !{!"branch_weights", i32 1, i32 2}
+// FE: ![[PD1]] = !{!"branch_weights", i32 1, i32 2}