[PATCH] Support using sample profiles with partial debug info.

[David Blaikie]

================
Comment at: lib/Transforms/Scalar/SampleProfile.cpp:662
@@ +661,3 @@
+    // leading back to \p F.
+    for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
+      BasicBlock *B = I;
----------------
Please use range-based-for loops.

================
Comment at: lib/Transforms/Scalar/SampleProfile.cpp:671
@@ +670,3 @@
+        if (Subprogram.describes(&F))
+          return Subprogram.getLineNumber();
+      }
----------------
If you find an instruction with DebugLoc, you don't need to keep searching - no matter what its subprogram node is.

This is what I tried to describe with the pseudocode I mentioned on IRC the other day.

for (basic blocks)
  for (instructions)
    if (debugloc.isvalid)
      if (getsubprogram(debugloc).describes(F))
        return subprogram.getLineNumber()
      else
        /* break out of all the loops & consider this a failure */

(maybe wrap all this in a function so you can more easily early-exit when you reach that situation)

Here's the invariant that I believe now holds:
If a function has debug info, the scope chain of all instructions in that function will lead to the function and nothing else.

So once you find one instruction with a debug loc, you don't need to examine any others - if it leads to this function, you're done, if it doesn't then this function doesn't have debug info.

================
Comment at: test/Transforms/SampleProfile/loc-tracking-only.ll:3
@@ +2,3 @@
+
+; This test is identical to calls.ll but it is missing the llvm.dbg.cu
+; annotation. This emulates the effect of the user having only used
----------------
Worth updating calls.ll itself instead of adding a new test? If you don't depend on the llvm.dbg.cu at all, it doesn't seem worthwhile to have two different tests, one with it and one without it.

http://reviews.llvm.org/D5887