Don't move llvm.localescape outside the entry block in the GCOV profiling pass

[marco-c]

Summary

This fixes https://bugs.llvm.org/show_bug.cgi?id=34714.

Patch by Marco Castelluccio

[rnk]

lgtm

lib/Transforms/Instrumentation/GCOVProfiling.cpp

550–552

This problematically assumes that all the allocas, dbg.declare, and localescape are all in a contiguous block, but that's a pre-existing issue that you don't need to fix. In practice, clang inserts localescape after allocas.

lib/Transforms/Instrumentation/GCOVProfiling.cpp

   return false;
 }
 
+static bool shouldKeepInEntry(BasicBlock::iterator It) {
+  if (isa<AllocaInst>(*It)) return true;
+  if (isa<DbgInfoIntrinsic>(*It)) return true;
+  if (auto *II = dyn_cast<IntrinsicInst>(It)) {
+    if (II->getIntrinsicID() == llvm::Intrinsic::localescape) return true;
+  }
+
+  return false;
+}
+
 void GCOVProfiler::emitProfileNotes() {
   NamedMDNode *CU_Nodes = M->getNamedMetadata("llvm.dbg.cu");
   if (!CU_Nodes) return;

       // single successor, so split the entry block to make sure of that.
       BasicBlock &EntryBlock = F.getEntryBlock();
       BasicBlock::iterator It = EntryBlock.begin();
-      while (isa<AllocaInst>(*It) || isa<DbgInfoIntrinsic>(*It))
+      while (shouldKeepInEntry(It))
         ++It;
       EntryBlock.splitBasicBlock(It);