AsmWriter: Avoid O(N^2) processing of metadata

Fix embarrassing bugs I introduced to the `SlotTracker` in or around
r235785.  I had us iterating through every instruction in a function
(and hitting a map in the LLVMContext) for every basic block in the
function.

While there, completely avoid the call to
`SlotTracker::processFunctionMetadata()` from
`SlotTracker::processFunction()` if we've speculatively done this
already in `SlotTracker::processModule()` by checking
`ShouldInitializeAllMetadata` (this wasn't an algorithmic problem, but
it's touching the same line of code).

Fixes PR24699.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247372 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 6 deletions

diff --git a/lib/IR/AsmWriter.cpp b/lib/IR/AsmWriter.cpp
index db7fd7a2324..56a002c0382 100644
--- a/lib/IR/AsmWriter.cpp
+++ b/lib/IR/AsmWriter.cpp
@@ -807,6 +807,10 @@ void SlotTracker::processFunction() {
   ST_DEBUG("begin processFunction!\n");
   fNext = 0;
 
+  // Process function metadata if it wasn't hit at the module-level.
+  if (!ShouldInitializeAllMetadata)
+    processFunctionMetadata(*TheFunction);
+
   // Add all the function arguments with no names.
   for(Function::const_arg_iterator AI = TheFunction->arg_begin(),
       AE = TheFunction->arg_end(); AI != AE; ++AI)
@@ -820,8 +824,6 @@ void SlotTracker::processFunction() {
     if (!BB.hasName())
       CreateFunctionSlot(&BB);
 
-    processFunctionMetadata(*TheFunction);
-
     for (auto &I : BB) {
       if (!I.getType()->isVoidTy() && !I.hasName())
         CreateFunctionSlot(&I);
@@ -849,11 +851,11 @@ void SlotTracker::processFunction() {
 
 void SlotTracker::processFunctionMetadata(const Function &F) {
   SmallVector<std::pair<unsigned, MDNode *>, 4> MDs;
-  for (auto &BB : F) {
-    F.getAllMetadata(MDs);
-    for (auto &MD : MDs)
-      CreateMetadataSlot(MD.second);
+  F.getAllMetadata(MDs);
+  for (auto &MD : MDs)
+    CreateMetadataSlot(MD.second);
 
+  for (auto &BB : F) {
     for (auto &I : BB)
       processInstructionMetadata(I);
   }