Remove unreachable blocks before splitting a coroutine.

The suspend-crossing algorithm is not correct in the presence of uses
that cannot be reached on some successor path from their defs.

llvm-svn: 368796

1 files changed, 19 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
index db318d858da..01357f0c8bd 100644
--- a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
+++ b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
@@ -55,6 +55,7 @@
 #include "llvm/Pass.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
@@ -1397,6 +1398,19 @@ static void splitRetconCoroutine(Function &F, coro::Shape &Shape,
   }
 }
 
+namespace {
+  class PrettyStackTraceFunction : public PrettyStackTraceEntry {
+    Function &F;
+  public:
+    PrettyStackTraceFunction(Function &F) : F(F) {}
+    void print(raw_ostream &OS) const override {
+      OS << "While splitting coroutine ";
+      F.printAsOperand(OS, /*print type*/ false, F.getParent());
+      OS << "\n";
+    }
+  };
+}
+
 static void splitCoroutine(Function &F, coro::Shape &Shape,
                            SmallVectorImpl<Function *> &Clones) {
   switch (Shape.ABI) {
@@ -1410,7 +1424,11 @@ static void splitCoroutine(Function &F, coro::Shape &Shape,
 }
 
 static void splitCoroutine(Function &F, CallGraph &CG, CallGraphSCC &SCC) {
-  EliminateUnreachableBlocks(F);
+  PrettyStackTraceFunction prettyStackTrace(F);
+
+  // The suspend-crossing algorithm in buildCoroutineFrame get tripped
+  // up by uses in unreachable blocks, so remove them as a first pass.
+  removeUnreachableBlocks(F);
 
   coro::Shape Shape(F);
   if (!Shape.CoroBegin)