[PHITransAddr] Don't assume that instruction operands are translatable

We can only PHI translate instructions.  In our attempt to PHI translate
a bitcast, we attempt to translate its operand; however, the operand
might be an argument or a global instead of an instruction.  Benignly
bail out when this happens.

This fixes PR24397.

Differential Revision: http://reviews.llvm.org/D11879

llvm-svn: 244418

lib/Analysis/PHITransAddr.cpp

@@ -374,9 +374,10 @@ InsertPHITranslatedSubExpr(Value *InVal, BasicBlock *CurBB,
   if (!Tmp.PHITranslateValue(CurBB, PredBB, &DT, /*MustDominate=*/true))
     return Tmp.getAddr();
 
-  // If we don't have an available version of this value, it must be an
-  // instruction.
-  Instruction *Inst = cast<Instruction>(InVal);
+  // We don't need to PHI translate values which aren't instructions.
+  auto *Inst = dyn_cast<Instruction>(InVal);
+  if (!Inst)
+    return nullptr;
 
   // Handle cast of PHI translatable value.
   if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {

test/Transforms/GVN/pr24397.ll

@@ -0,0 +1,18 @@
+; RUN: opt -basicaa -gvn -disable-output < %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define i64 @foo(i64** %arrayidx) {
+entry:
+  %p = load i64*, i64** %arrayidx, align 8
+  %cmpnull = icmp eq i64* %p, null
+  br label %BB2
+
+entry2:                                           ; No predecessors!
+  br label %BB2
+
+BB2:                                              ; preds = %entry2, %entry
+  %bc = bitcast i64** %arrayidx to i64*
+  %load = load i64, i64* %bc, align 8
+  ret i64 %load
+}