Reapply: [DebugInfo] Recover debug intrinsics when killing duplicated/empty...

basic blocks

Originally applied in 72ce759928e6dfee6a9efa310b966c19722352ba.

Fixed a build failure caused by incorrect use of cast instead of
dyn_cast.

This reverts commit 8b0780f795eb58fca0a2456e308adaaa1a0b5013.

1 files changed, 42 insertions, 17 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index d93ca4f04cd..681c344f87a 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -13,6 +13,7 @@
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SetOperations.h"
@@ -38,6 +39,7 @@
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalValue.h"
@@ -1250,14 +1252,38 @@ static bool HoistThenElseCodeToIf(BranchInst *BI,
 
   Instruction *I1 = &*BB1_Itr++, *I2 = &*BB2_Itr++;
   // Skip debug info if it is not identical.
-  DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
-  DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
-  if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
-    while (isa<DbgInfoIntrinsic>(I1))
-      I1 = &*BB1_Itr++;
-    while (isa<DbgInfoIntrinsic>(I2))
-      I2 = &*BB2_Itr++;
-  }
+
+  // If the terminator instruction is hoisted, and any variable locations have
+  // non-identical debug intrinsics, then those variable locations must be set
+  // as undef.
+  // FIXME: If each block contains identical debug variable intrinsics in a
+  // different order, they will be considered non-identical and be dropped.
+  MapVector<DebugVariable, DbgVariableIntrinsic *> UndefDVIs;
+
+  auto SkipDbgInfo = [&UndefDVIs](Instruction *&I,
+                                  BasicBlock::iterator &BB_Itr) {
+    while (isa<DbgInfoIntrinsic>(I)) {
+      if (DbgVariableIntrinsic *DVI = dyn_cast<DbgVariableIntrinsic>(I))
+        UndefDVIs.insert(
+            {DebugVariable(DVI->getVariable(), DVI->getExpression(),
+                           DVI->getDebugLoc()->getInlinedAt()),
+             DVI});
+      I = &*BB_Itr++;
+    }
+  };
+
+  auto SkipNonIdenticalDbgInfo =
+      [&BB1_Itr, &BB2_Itr, &SkipDbgInfo](Instruction *&I1, Instruction *&I2) {
+        DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
+        DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
+        if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
+          SkipDbgInfo(I1, BB1_Itr);
+          SkipDbgInfo(I2, BB2_Itr);
+        }
+      };
+
+  SkipNonIdenticalDbgInfo(I1, I2);
+
   // FIXME: Can we define a safety predicate for CallBr?
   if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
       (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) ||
@@ -1330,15 +1356,7 @@ static bool HoistThenElseCodeToIf(BranchInst *BI,
 
     I1 = &*BB1_Itr++;
     I2 = &*BB2_Itr++;
-    // Skip debug info if it is not identical.
-    DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
-    DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
-    if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
-      while (isa<DbgInfoIntrinsic>(I1))
-        I1 = &*BB1_Itr++;
-      while (isa<DbgInfoIntrinsic>(I2))
-        I2 = &*BB2_Itr++;
-    }
+    SkipNonIdenticalDbgInfo(I1, I2);
   } while (I1->isIdenticalToWhenDefined(I2));
 
   return true;
@@ -1374,6 +1392,13 @@ HoistTerminator:
   }
 
   // Okay, it is safe to hoist the terminator.
+  for (auto DIVariableInst : UndefDVIs) {
+    DbgVariableIntrinsic *DVI = DIVariableInst.second;
+    DVI->moveBefore(BI);
+    if (DVI->getVariableLocation())
+      setDbgVariableUndef(DVI);
+  }
+
   Instruction *NT = I1->clone();
   BIParent->getInstList().insert(BI->getIterator(), NT);
   if (!NT->getType()->isVoidTy()) {