[llvm] ef50c07 - [JITLink] Add a new PostAllocationPasses list.

[Lang Hames via llvm-commits]

Author: Lang Hames
Date: 2021-01-12T11:57:07+11:00
New Revision: ef50c07b1fad368f6a8d326b4f73dd531009dca4

URL: https://github.com/llvm/llvm-project/commit/ef50c07b1fad368f6a8d326b4f73dd531009dca4
DIFF: https://github.com/llvm/llvm-project/commit/ef50c07b1fad368f6a8d326b4f73dd531009dca4.diff

LOG: [JITLink] Add a new PostAllocationPasses list.

Passes in the new PostAllocationPasses list will run immediately after memory
allocation and address assignment for defined symbols, and before
JITLinkContext::notifyResolved is called. These passes can set up state
associated with the addresses of defined symbols before any query for these
addresses completes.

Added: 
    

Modified: 
    llvm/include/llvm/ExecutionEngine/JITLink/JITLink.h
    llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp

Removed: 
    


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diff  --git a/llvm/include/llvm/ExecutionEngine/JITLink/JITLink.h b/llvm/include/llvm/ExecutionEngine/JITLink/JITLink.h
index 72daf76b501a..e8c0e28b83aa 100644
--- a/llvm/include/llvm/ExecutionEngine/JITLink/JITLink.h
+++ b/llvm/include/llvm/ExecutionEngine/JITLink/JITLink.h
@@ -1223,11 +1223,27 @@ struct PassConfiguration {
   /// Notable use cases: Building GOT, stub, and TLV symbols.
   LinkGraphPassList PostPrunePasses;
 
+  /// Post-allocation passes.
+  ///
+  /// These passes are called on the graph after memory has been allocated and
+  /// defined nodes have been assigned their final addresses, but before the
+  /// context has been notified of these addresses. At this point externals
+  /// have not been resolved, and symbol content has not yet been copied into
+  /// working memory.
+  ///
+  /// Notable use cases: Setting up data structures associated with addresses
+  /// of defined symbols (e.g. a mapping of __dso_handle to JITDylib* for the
+  /// JIT runtime) -- using a PostAllocationPass for this ensures that the
+  /// data structures are in-place before any query for resolved symbols
+  /// can complete.
+  LinkGraphPassList PostAllocationPasses;
+
   /// Pre-fixup passes.
   ///
   /// These passes are called on the graph after memory has been allocated,
-  /// content copied into working memory, and nodes have been assigned their
-  /// final addresses, but before any fixups have been applied.
+  /// content copied into working memory, and all nodes (including externals)
+  /// have been assigned their final addresses, but before any fixups have been
+  /// applied.
   ///
   /// Notable use cases: Late link-time optimizations like GOT and stub
   /// elimination.

diff  --git a/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp b/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp
index d6ad364add12..7a5e014f223d 100644
--- a/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp
+++ b/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp
@@ -55,6 +55,16 @@ void JITLinkerBase::linkPhase1(std::unique_ptr<JITLinkerBase> Self) {
   if (auto Err = allocateSegments(Layout))
     return Ctx->notifyFailed(std::move(Err));
 
+  LLVM_DEBUG({
+    dbgs() << "Link graph \"" << G->getName()
+           << "\" before post-allocation passes:\n";
+    dumpGraph(dbgs());
+  });
+
+  // Run post-allocation passes.
+  if (auto Err = runPasses(Passes.PostAllocationPasses))
+    return Ctx->notifyFailed(std::move(Err));
+
   // Notify client that the defined symbols have been assigned addresses.
   LLVM_DEBUG(
       { dbgs() << "Resolving symbols defined in " << G->getName() << "\n"; });
@@ -110,7 +120,7 @@ void JITLinkerBase::linkPhase2(std::unique_ptr<JITLinkerBase> Self,
 
   LLVM_DEBUG({
     dbgs() << "Link graph \"" << G->getName()
-           << "\" before post-allocation passes:\n";
+           << "\" before pre-fixup passes:\n";
     dumpGraph(dbgs());
   });