[PATCH] D102963: CoroSplit: Replace ad-hoc implementation of reachability with API from CFG.h

[Adrian Prantl via Phabricator via llvm-commits]

aprantl created this revision.
aprantl added reviewers: vsk, kastiglione, ChuanqiXu, lxfind.
Herald added a subscriber: hiraditya.
aprantl requested review of this revision.
Herald added a project: LLVM.

The current ad-hoc implementation used to determine whether a basic block is unreachable doesn't work correctly in the general case (for example it won't detect successors of unreachable blocks as unreachable). This patch replaces it with the correct API that uses a DominatorTree to answer the question correctly and quickly.

rdar://77181156


https://reviews.llvm.org/D102963

Files:
  llvm/lib/Transforms/Coroutines/CoroSplit.cpp
  llvm/test/Transforms/Coroutines/coro-debug.ll


Index: llvm/test/Transforms/Coroutines/coro-debug.ll
===================================================================
--- llvm/test/Transforms/Coroutines/coro-debug.ll
+++ llvm/test/Transforms/Coroutines/coro-debug.ll
@@ -20,6 +20,7 @@
   store i8* %2, i8** %coro_hdl, align 8, !dbg !16
   %3 = call i8 @llvm.coro.suspend(token none, i1 false), !dbg !17
   %conv = sext i8 %3 to i32, !dbg !17
+  %late_local = alloca i32, align 4
   call void @coro.devirt.trigger(i8* null)
   switch i32 %conv, label %sw.default [
     i32 0, label %sw.bb
@@ -35,6 +36,10 @@
   call void @llvm.dbg.declare(metadata i32* %x.addr, metadata !12, metadata !13), !dbg !14
   call void @llvm.dbg.declare(metadata i8** %coro_hdl, metadata !15, metadata !13), !dbg !16
   call void @llvm.dbg.declare(metadata i8* null, metadata !28, metadata !13), !dbg !16
+  call void @llvm.dbg.declare(metadata i32* %late_local, metadata !29, metadata !13), !dbg !16
+  br label %next, !dbg !18
+
+next:
   br label %sw.epilog, !dbg !18
 
 sw.bb1:                                           ; preds = %entry
@@ -58,6 +63,7 @@
 coro_Suspend:                                     ; preds = %coro_Cleanup, %sw.default
   %7 = call i1 @llvm.coro.end(i8* null, i1 false) #7, !dbg !24
   %8 = load i8*, i8** %coro_hdl, align 8, !dbg !24
+  store i32 0, i32* %late_local, !dbg !24
   ret i8* %8, !dbg !24
 }
 
@@ -138,6 +144,7 @@
 !26 = !DILocalVariable(name: "direct_const", scope: !6, file: !7, line: 55, type: !11)
 !27 = !DILocalVariable(name: "undefined", scope: !6, file: !7, line: 55, type: !11)
 !28 = !DILocalVariable(name: "null", scope: !6, file: !7, line: 55, type: !11)
+!29 = !DILocalVariable(name: "partial_dead", scope: !6, file: !7, line: 55, type: !11)
 
 ; CHECK: define i8* @f(i32 %x) #0 !dbg ![[ORIG:[0-9]+]]
 ; CHECK: define internal fastcc void @f.resume(%f.Frame* noalias nonnull align 8 dereferenceable(32) %FramePtr) #0 !dbg ![[RESUME:[0-9]+]]
@@ -149,6 +156,8 @@
 ; CHECK: store %f.Frame* {{.*}}, %f.Frame** %[[DBG_PTR]]
 ; CHECK-NOT: alloca %struct.test*
 ; CHECK: call void @llvm.dbg.declare(metadata i32 0, metadata ![[RESUME_CONST:[0-9]+]], metadata !DIExpression())
+; Note that keeping the undef value here could be acceptable, too.
+; CHECK-NOT: call void @llvm.dbg.declare(metadata i32* undef, metadata !{{[0-9]+}}, metadata !DIExpression())
 ; CHECK: call void @coro.devirt.trigger(i8* null)
 ; CHECK: define internal fastcc void @f.destroy(%f.Frame* noalias nonnull align 8 dereferenceable(32) %FramePtr) #0 !dbg ![[DESTROY:[0-9]+]]
 ; CHECK: define internal fastcc void @f.cleanup(%f.Frame* noalias nonnull align 8 dereferenceable(32) %FramePtr) #0 !dbg ![[CLEANUP:[0-9]+]]
Index: llvm/lib/Transforms/Coroutines/CoroSplit.cpp
===================================================================
--- llvm/lib/Transforms/Coroutines/CoroSplit.cpp
+++ llvm/lib/Transforms/Coroutines/CoroSplit.cpp
@@ -26,6 +26,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/Analysis/CFG.h"
 #include "llvm/Analysis/CallGraph.h"
 #include "llvm/Analysis/CallGraphSCCPass.h"
 #include "llvm/Analysis/LazyCallGraph.h"
@@ -37,6 +38,7 @@
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalValue.h"
 #include "llvm/IR/GlobalVariable.h"
@@ -658,8 +660,11 @@
 
   // Remove all salvaged dbg.declare intrinsics that became
   // either unreachable or stale due to the CoroSplit transformation.
+  DominatorTree DomTree(*NewF);
+  SmallDenseMap<BasicBlock *, bool, 8> UnreachableCache;
   auto IsUnreachableBlock = [&](BasicBlock *BB) {
-    return BB->hasNPredecessors(0) && BB != &NewF->getEntryBlock();
+    return !isPotentiallyReachable(&NewF->getEntryBlock(), BB, nullptr,
+                                   &DomTree);
   };
   for (DbgVariableIntrinsic *DVI : Worklist) {
     if (IsUnreachableBlock(DVI->getParent()))


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