[llvm] 4cba0a4 - CoroSplit: Replace ad-hoc implementation of reachability with API from CFG.h

[Adrian Prantl via llvm-commits]

Author: Adrian Prantl
Date: 2021-05-24T09:18:33-07:00
New Revision: 4cba0a4f11e40f447545434aa57effc4e39a8a57

URL: https://github.com/llvm/llvm-project/commit/4cba0a4f11e40f447545434aa57effc4e39a8a57
DIFF: https://github.com/llvm/llvm-project/commit/4cba0a4f11e40f447545434aa57effc4e39a8a57.diff

LOG: CoroSplit: Replace ad-hoc implementation of reachability with API from CFG.h

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

Differential Revision: https://reviews.llvm.org/D102963

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
index 4efebfd809cb7..a1c0f4f8c0add 100644
--- a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
+++ b/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 @@ void CoroCloner::salvageDebugInfo() {
 
   // 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()))

diff  --git a/llvm/test/Transforms/Coroutines/coro-debug.ll b/llvm/test/Transforms/Coroutines/coro-debug.ll
index c34428b3ed404..d38c52835acd0 100644
--- a/llvm/test/Transforms/Coroutines/coro-debug.ll
+++ b/llvm/test/Transforms/Coroutines/coro-debug.ll
@@ -20,6 +20,7 @@ entry:
   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 @@ sw.bb:                                            ; preds = %entry
   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_Cleanup:                                     ; preds = %sw.epilog, %sw.bb1
 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 @@ attributes #7 = { noduplicate }
 !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 @@ attributes #7 = { noduplicate }
 ; 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]+]]