[MemProf] Add dot graph dumping immediately after stack node update (#143025)

To aid in debugging, (optionally) dump the dot graph immediately after
the stack update phase (which matches nodes to interior callsites) and
before we cleanup mismatched callee edges (either via tail call fixup,
indirect call fixup, or nulling otherwise).

Author: teresajohnson

llvm/lib/Transforms/IPO/MemProfContextDisambiguation.cpp

@@ -2183,6 +2183,9 @@ ModuleCallsiteContextGraph::ModuleCallsiteContextGraph(
 
   updateStackNodes();
 
+  if (ExportToDot)
+    exportToDot("poststackupdate");
+
   handleCallsitesWithMultipleTargets();
 
   markBackedges();
@@ -2285,6 +2288,9 @@ IndexCallsiteContextGraph::IndexCallsiteContextGraph(
 
   updateStackNodes();
 
+  if (ExportToDot)
+    exportToDot("poststackupdate");
+
   handleCallsitesWithMultipleTargets();
 
   markBackedges();

llvm/test/Transforms/MemProfContextDisambiguation/duplicate-context-ids.ll

@@ -64,6 +64,10 @@
 ; RUN:  --check-prefix=STATS --check-prefix=REMARKS
 
 ; RUN:  cat %t.ccg.prestackupdate.dot | FileCheck %s --check-prefix=DOTPRE
+;; There are no changes for this test case in between from immediately after
+;; the stack update through the end of graph finalization, so the
+;; corresponding dot graphs should be identical.
+; RUN:  cat %t.ccg.poststackupdate.dot | FileCheck %s --check-prefix=DOTPOST
 ; RUN:  cat %t.ccg.postbuild.dot | FileCheck %s --check-prefix=DOTPOST
 ;; We should clone D once for the cold allocations via C.
 ; RUN:  cat %t.ccg.cloned.dot | FileCheck %s --check-prefix=DOTCLONED
@@ -313,8 +317,8 @@ attributes #6 = { builtin }
 ; DOTPRE: }
 
 
-; DOTPOST:digraph "postbuild" {
-; DOTPOST:	label="postbuild";
+; DOTPOST:digraph "post
+; DOTPOST:	label="post
 ; DOTPOST:	Node[[D:0x[a-z0-9]+]] [shape=record,tooltip="N[[D]] ContextIds: 1 2 3 4",fillcolor="mediumorchid1",style="filled",label="{OrigId: Alloc0\n_Z1Dv -\> _Znam}"];
 ; DOTPOST:	Node[[F:0x[a-z0-9]+]] [shape=record,tooltip="N[[F]] ContextIds: 2",fillcolor="brown1",style="filled",label="{OrigId: 13543580133643026784\n_Z1Fv -\> _Z1Dv}"];
 ; DOTPOST:	Node[[F]] -> Node[[D]][tooltip="ContextIds: 2",fillcolor="brown1"

llvm/test/Transforms/MemProfContextDisambiguation/tailcall-nonunique.ll

@@ -6,11 +6,20 @@
 ; REQUIRES: asserts
 
 ; RUN: opt -passes=memprof-context-disambiguation -supports-hot-cold-new \
+; RUN:	-memprof-export-to-dot -memprof-dot-file-path-prefix=%t. \
 ; RUN:  -stats -debug %s -S 2>&1 | FileCheck %s --check-prefix=STATS \
 ; RUN:  --check-prefix=IR --check-prefix=DEBUG
 
 ; DEBUG: Not found through unique tail call chain: _Z3barv from main that actually called xyz (found multiple possible chains)
 
+;; Graph fixup should have nulled the call in the node that could not be
+;; resolved via tail call fixup. That happens in between the initial
+;; stack update and the end of graph building.
+; RUN:  cat %t.ccg.poststackupdate.dot | FileCheck %s --check-prefix=DOTPOSTSTACKUPDATE
+; DOTPOSTSTACKUPDATE: {OrigId: 15025054523792398438\nmain -\> xyz}
+; RUN:  cat %t.ccg.postbuild.dot | FileCheck %s --check-prefix=DOTPOSTBUILD
+; DOTPOSTBUILD: {OrigId: 15025054523792398438\nnull call (external)}
+
 ;; Check that all calls in the IR are to the original functions, leading to a
 ;; non-cold operator new call.