[msan] Avoid unnecessary PC increment/decrement

[kda]

Is the idea here, that since the name is being preserved, it is not necessary to have the line number where the variable is declared?
I feel like the way it is currently implemented matches the heap tracking, as the stack points to where the allocation is done.

Also, with introduction of flag to suppress variable names, then better to get the line right.

resolved: nevermind, convinced valid verbally.

compiler-rt/lib/msan/msan.cpp

void __msan_load_unpoisoned(const void *src, uptr size, void *dst) {
   __msan_unpoison(dst, size);
 }
 
 void __msan_set_origin(const void *a, uptr size, u32 origin) {
   if (__msan_get_track_origins()) SetOrigin(a, size, origin);
 }
 
 void __msan_set_alloca_origin(void *a, uptr size, char *descr) {
-  SetAllocaOrigin(a, size, descr,
-                  StackTrace::GetPreviousInstructionPc(GET_CALLER_PC()));
+  SetAllocaOrigin(a, size, descr, GET_CALLER_PC());
 }
 
 void __msan_set_alloca_origin4(void *a, uptr size, char *descr, uptr pc) {
   // Intentionally ignore pc and use return address. This function is here for
   // compatibility, in case program is linked with library instrumented by
   // older clang.
-  SetAllocaOrigin(a, size, descr,
-                  StackTrace::GetPreviousInstructionPc(GET_CALLER_PC()));
+  SetAllocaOrigin(a, size, descr, GET_CALLER_PC());
 }
 
 u32 __msan_chain_origin(u32 id) {
   GET_CALLER_PC_BP_SP;
   (void)sp;
   GET_STORE_STACK_TRACE_PC_BP(pc, bp);
   return ChainOrigin(id, &stack);
 }

compiler-rt/lib/msan/msan_report.cpp

 static void DescribeStackOrigin(const char *so, uptr pc) {
   Decorator d;
   Printf("%s", d.Origin());
   Printf(
       "  %sUninitialized value was created by an allocation of '%s%s%s'"
       " in the stack frame%s\n",
       d.Origin(), d.Name(), so, d.Origin(), d.Default());
 
-  if (pc) {
-    // For some reason function address in LLVM IR is 1 less then the address
-    // of the first instruction.
-    pc = StackTrace::GetNextInstructionPc(pc);
+  if (pc)
     StackTrace(&pc, 1).Print();
-  }
-}
 
 static void DescribeOrigin(u32 id) {
   VPrintf(1, "  raw origin id: %d\n", id);
   Decorator d;
   Origin o = Origin::FromRawId(id);
   while (o.isChainedOrigin()) {
     StackTrace stack;
     o = o.getNextChainedOrigin(&stack);