DI: Reverse direction of subprogram -> function edge.

Previously, subprograms contained a metadata reference to the function they
described. Because most clients need to get or set a subprogram for a given
function rather than the other way around, this created unneeded inefficiency.

For example, many passes needed to call the function llvm::makeSubprogramMap()
to build a mapping from functions to subprograms, and the IR linker needed to
fix up function references in a way that caused quadratic complexity in the IR
linking phase of LTO.

This change reverses the direction of the edge by storing the subprogram as
function-level metadata and removing DISubprogram's function field.

Since this is an IR change, a bitcode upgrade has been provided.

Fixes PR23367. An upgrade script for textual IR for out-of-tree clients is
attached to the PR.

Differential Revision: http://reviews.llvm.org/D14265

llvm-svn: 252219

1 files changed, 35 insertions, 42 deletions

diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index f64d4e2fddc..813f9ca6744 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -937,13 +937,6 @@ void Verifier::visitDISubprogram(const DISubprogram &N) {
     Assert(isa<DISubroutineType>(T), "invalid subroutine type", &N, T);
   Assert(isTypeRef(N, N.getRawContainingType()), "invalid containing type", &N,
          N.getRawContainingType());
-  if (auto *RawF = N.getRawFunction()) {
-    auto *FMD = dyn_cast<ConstantAsMetadata>(RawF);
-    auto *F = FMD ? FMD->getValue() : nullptr;
-    auto *FT = F ? dyn_cast<PointerType>(F->getType()) : nullptr;
-    Assert(F && FT && isa<FunctionType>(FT->getElementType()),
-           "invalid function", &N, F, FT);
-  }
   if (auto *Params = N.getRawTemplateParams())
     visitTemplateParams(N, *Params);
   if (auto *S = N.getRawDeclaration()) {
@@ -963,41 +956,6 @@ void Verifier::visitDISubprogram(const DISubprogram &N) {
 
   if (N.isDefinition())
     Assert(N.isDistinct(), "subprogram definitions must be distinct", &N);
-
-  auto *F = N.getFunction();
-  if (!F)
-    return;
-
-  // Check that all !dbg attachments lead to back to N (or, at least, another
-  // subprogram that describes the same function).
-  //
-  // FIXME: Check this incrementally while visiting !dbg attachments.
-  // FIXME: Only check when N is the canonical subprogram for F.
-  SmallPtrSet<const MDNode *, 32> Seen;
-  for (auto &BB : *F)
-    for (auto &I : BB) {
-      // Be careful about using DILocation here since we might be dealing with
-      // broken code (this is the Verifier after all).
-      DILocation *DL =
-          dyn_cast_or_null<DILocation>(I.getDebugLoc().getAsMDNode());
-      if (!DL)
-        continue;
-      if (!Seen.insert(DL).second)
-        continue;
-
-      DILocalScope *Scope = DL->getInlinedAtScope();
-      if (Scope && !Seen.insert(Scope).second)
-        continue;
-
-      DISubprogram *SP = Scope ? Scope->getSubprogram() : nullptr;
-      if (SP && !Seen.insert(SP).second)
-        continue;
-
-      // FIXME: Once N is canonical, check "SP == &N".
-      Assert(SP->describes(F),
-             "!dbg attachment points at wrong subprogram for function", &N, F,
-             &I, DL, Scope, SP);
-    }
 }
 
 void Verifier::visitDILexicalBlockBase(const DILexicalBlockBase &N) {
@@ -1812,6 +1770,41 @@ void Verifier::visitFunction(const Function &F) {
              (F.isDeclaration() && F.hasExternalLinkage()) ||
              F.hasAvailableExternallyLinkage(),
          "Function is marked as dllimport, but not external.", &F);
+
+  auto *N = F.getSubprogram();
+  if (!N)
+    return;
+
+  // Check that all !dbg attachments lead to back to N (or, at least, another
+  // subprogram that describes the same function).
+  //
+  // FIXME: Check this incrementally while visiting !dbg attachments.
+  // FIXME: Only check when N is the canonical subprogram for F.
+  SmallPtrSet<const MDNode *, 32> Seen;
+  for (auto &BB : F)
+    for (auto &I : BB) {
+      // Be careful about using DILocation here since we might be dealing with
+      // broken code (this is the Verifier after all).
+      DILocation *DL =
+          dyn_cast_or_null<DILocation>(I.getDebugLoc().getAsMDNode());
+      if (!DL)
+        continue;
+      if (!Seen.insert(DL).second)
+        continue;
+
+      DILocalScope *Scope = DL->getInlinedAtScope();
+      if (Scope && !Seen.insert(Scope).second)
+        continue;
+
+      DISubprogram *SP = Scope ? Scope->getSubprogram() : nullptr;
+      if (SP && !Seen.insert(SP).second)
+        continue;
+
+      // FIXME: Once N is canonical, check "SP == &N".
+      Assert(SP->describes(&F),
+             "!dbg attachment points at wrong subprogram for function", N, &F,
+             &I, DL, Scope, SP);
+    }
 }
 
 // verifyBasicBlock - Verify that a basic block is well formed...