From 9e66c4ec127ef6e73f1bafe06fe3fba45d59feee Mon Sep 17 00:00:00 2001
From: Alina Sbirlea <asbirlea@google.com>
Date: Thu, 23 Jan 2020 14:21:08 -0800
Subject: [Utils] Use WeakTrackingVH in vector used as scratch storage.

The utility method RecursivelyDeleteTriviallyDeadInstructions receives
as input a vector of Instructions, where all inputs are valid
instructions. This same vector is used as a scratch storage (per the
header comment) to recursively delete instructions. If an instruction is
added as an operand of multiple other instructions, it may be added twice,
then deleted once, then the second reference in the vector is invalid.
Switch to using a Vector<WeakTrackingVH>.
This change facilitates a clean-up in LoopStrengthReduction.
---
 llvm/lib/Transforms/Utils/Local.cpp | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

(limited to 'llvm/lib/Transforms/Utils/Local.cpp')

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 5b188fc..10afed3 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -443,7 +443,7 @@ bool llvm::RecursivelyDeleteTriviallyDeadInstructions(
   if (!I || !isInstructionTriviallyDead(I, TLI))
     return false;
 
-  SmallVector<Instruction*, 16> DeadInsts;
+  SmallVector<WeakTrackingVH, 16> DeadInsts;
   DeadInsts.push_back(I);
   RecursivelyDeleteTriviallyDeadInstructions(DeadInsts, TLI, MSSAU);
 
@@ -451,21 +451,24 @@ bool llvm::RecursivelyDeleteTriviallyDeadInstructions(
 }
 
 void llvm::RecursivelyDeleteTriviallyDeadInstructions(
-    SmallVectorImpl<Instruction *> &DeadInsts, const TargetLibraryInfo *TLI,
+    SmallVectorImpl<WeakTrackingVH> &DeadInsts, const TargetLibraryInfo *TLI,
     MemorySSAUpdater *MSSAU) {
   // Process the dead instruction list until empty.
   while (!DeadInsts.empty()) {
-    Instruction &I = *DeadInsts.pop_back_val();
-    assert(I.use_empty() && "Instructions with uses are not dead.");
-    assert(isInstructionTriviallyDead(&I, TLI) &&
+    Value *V = DeadInsts.pop_back_val();
+    Instruction *I = cast_or_null<Instruction>(V);
+    if (!I)
+      continue;
+    assert(isInstructionTriviallyDead(I, TLI) &&
            "Live instruction found in dead worklist!");
+    assert(I->use_empty() && "Instructions with uses are not dead.");
 
     // Don't lose the debug info while deleting the instructions.
-    salvageDebugInfo(I);
+    salvageDebugInfo(*I);
 
     // Null out all of the instruction's operands to see if any operand becomes
     // dead as we go.
-    for (Use &OpU : I.operands()) {
+    for (Use &OpU : I->operands()) {
       Value *OpV = OpU.get();
       OpU.set(nullptr);
 
@@ -480,9 +483,9 @@ void llvm::RecursivelyDeleteTriviallyDeadInstructions(
           DeadInsts.push_back(OpI);
     }
     if (MSSAU)
-      MSSAU->removeMemoryAccess(&I);
+      MSSAU->removeMemoryAccess(I);
 
-    I.eraseFromParent();
+    I->eraseFromParent();
   }
 }
 
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