[ValueTracking] Allow context-sensitive nullness check for non-pointers

Summary:
Same as D60846 and D69571 but with a fix for the problem encountered
after them. Both times it was a missing context adjustment in the
handling of PHI nodes.

The reproducers created from the bugs that caused the old commits to be
reverted are included.

Reviewers: nikic, nlopes, mkazantsev, spatel, dlrobertson, uabelho, hakzsam, hans

Subscribers: hiraditya, bollu, asbirlea, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71181

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 22a76a05595..c27e2567d5f 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -543,10 +543,16 @@ static Value *ThreadCmpOverPHI(CmpInst::Predicate Pred, Value *LHS, Value *RHS,
 
   // Evaluate the BinOp on the incoming phi values.
   Value *CommonValue = nullptr;
-  for (Value *Incoming : PI->incoming_values()) {
+  for (unsigned u = 0, e = PI->getNumIncomingValues(); u < e; ++u) {
+    Value *Incoming = PI->getIncomingValue(u);
+    Instruction *InTI = PI->getIncomingBlock(u)->getTerminator();
     // If the incoming value is the phi node itself, it can safely be skipped.
     if (Incoming == PI) continue;
-    Value *V = SimplifyCmpInst(Pred, Incoming, RHS, Q, MaxRecurse);
+    // Change the context instruction to the "edge" that flows into the phi.
+    // This is important because that is where incoming is actually "evaluated"
+    // even though it is used later somewhere else.
+    Value *V = SimplifyCmpInst(Pred, Incoming, RHS, Q.getWithInstruction(InTI),
+                               MaxRecurse);
     // If the operation failed to simplify, or simplified to a different value
     // to previously, then give up.
     if (!V || (CommonValue && V != CommonValue))