Teach instsimplify to gracefully degrade in the presence of instructions

not attched to a basic block or function. There are conservatively
correct answers in these cases, and this makes the analysis more useful
in contexts where we have a partially formed bit of IR.

I don't have any way to test this directly... suggestions welcome here,
but I'm not seeing anything sadly. I only found this using a subsequent
patch to the inliner which runs instsimplify on partially inlined
instructions, and even then only on a quite large program. I never got
a reasonable testcase out of it, and anything I do get is likely to be
quite fragile due to requiring an interaction of two different passes,
and the only result being a segfault if it goes wrong.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153176 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index f8d159dc43847a2a514182cb5b94638df4f0e3f8..72e33d18621c2da9e28e29ec229aa89c45601133 100644 (file)
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -95,6 +95,12 @@ static bool ValueDominatesPHI(Value *V, PHINode *P, const DominatorTree *DT) {
     // Arguments and constants dominate all instructions.
     return true;
 
+  // If we are processing instructions (and/or basic blocks) that have not been
+  // fully added to a function, the parent nodes may still be null. Simply
+  // return the conservative answer in these cases.
+  if (!I->getParent() || !P->getParent() || !I->getParent()->getParent())
+    return false;
+
   // If we have a DominatorTree then do a precise test.
   if (DT) {
     if (!DT->isReachableFromEntry(P->getParent()))