[PGO][HIP] Stop pulling ROCm.o into every PGO host link (llvm#200101)

PR llvm#177665 added an unconditional `extern` reference to
`__llvm_profile_hip_collect_device_data` from `InstrProfilingFile.c`,
which forces `InstrProfilingPlatformROCm.o` (and its sanitizer_common /
interception dependencies) out of `libclang_rt.profile.a` in every PGO
binary. That breaks bots without `-lpthread` and races dlsym/PLT state
in non-HIP programs via the interceptor constructor.

Fix:
- Declare the hook `COMPILER_RT_WEAK` and gate the call on its address.
No `COMPILER_RT_VISIBILITY`: a hidden weak-undef function would be
non-preemptible and the address test would fold to true.
- Gate `installHipModuleInterceptors` on `dlsym(hipModuleLoad)` so the
constructor is a no-op if `ROCm.o` is still pulled in.

Fixes:
- https://lab.llvm.org/buildbot/#/builders/66/builds/31311
- https://lab.llvm.org/buildbot/#/builders/174/builds/36180

Verified:
- `check-profile` 134/134 pass.
- `nm` on a non-HIP `clang -fprofile-generate` binary: zero
`installHip`/`ROCm`/`sanitizer`/`hip_collect` symbols.
- HIP offload PGO end-to-end on gfx1101 (compile → run → `llvm-profdata
merge` → `llvm-cov`) still works; interceptor installs, device profile
collected via shared API.

Author: yxsamliu

compiler-rt/lib/profile/InstrProfilingFile.c

@@ -41,9 +41,20 @@
 #include "InstrProfilingPort.h"
 #include "InstrProfilingUtil.h"
 
-/* HIP / offload collection hook implemented in InstrProfilingPlatformROCm.c.
- * It is a no-op when no offload profile data was registered. */
+/* Weak so non-HIP programs do not force InstrProfilingPlatformROCm.o (and its
+ * transitive sanitizer_common / interception dependencies) into the host link
+ * out of libclang_rt.profile.a. HIP programs emit strong references to other
+ * ROCm-runtime symbols (e.g. __llvm_profile_offload_register_shadow_variable)
+ * that pull in the strong definition.
+ * No COMPILER_RT_VISIBILITY: a hidden weak-undefined symbol is non-preemptible
+ * and the address test at the call site would fold to true.
+ * Windows: __declspec(selectany) is data-only, and the ROCm interceptor path
+ * is not used there, so keep the original strong extern. */
+#if defined(_WIN32)
 extern int __llvm_profile_hip_collect_device_data(void);
+#else
+__attribute__((weak)) int __llvm_profile_hip_collect_device_data(void);
+#endif
 
 /* From where is profile name specified.
  * The order the enumerators define their
@@ -1202,10 +1213,16 @@ int __llvm_profile_write_file(void) {
   if (rc)
     PROF_ERR("Failed to write file \"%s\": %s\n", Filename, strerror(errno));
 
-  /* No-op when no HIP shadow variables or dynamic modules are registered,
-   * or when the HIP runtime is not loaded. Warning on failure is handled
-   * inside the callee so non-HIP programs do not see spurious noise. */
+  /* On non-Windows the declaration is weak: only invoked when
+   * InstrProfilingPlatformROCm.o is in the link, which happens when the program
+   * references other ROCm-runtime symbols (HIP-with-PGO). Warning on failure is
+   * handled inside the callee. */
+#if defined(_WIN32)
   (void)__llvm_profile_hip_collect_device_data();
+#else
+  if (&__llvm_profile_hip_collect_device_data)
+    (void)__llvm_profile_hip_collect_device_data();
+#endif
 
   // Restore SIGKILL.
   if (PDeathSig == 1)

compiler-rt/lib/profile/InstrProfilingPlatformROCm.cpp

@@ -24,6 +24,7 @@ extern "C" {
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 #else
+#include <dlfcn.h>
 #include <pthread.h>
 #endif
 
@@ -878,6 +879,12 @@ INTERCEPTOR(int, hipModuleUnload, void *module) {
 }
 
 __attribute__((constructor)) static void installHipModuleInterceptors() {
+  /* Skip when the HIP runtime is not loaded. INTERCEPT_FUNCTION uses the
+   * sanitizer interception framework, which can perturb dlsym/PLT state for
+   * the rest of the process even when the target symbol is absent; non-HIP
+   * programs linked with libclang_rt.profile.a must see zero side effects. */
+  if (!dlsym(RTLD_DEFAULT, "hipModuleLoad"))
+    return;
   if (!INTERCEPT_FUNCTION(hipModuleLoad))
     return;
   if (isVerboseMode())