SROA: Don't crash on a select with two identical operands.

This is an edge case that can happen if we modify a chain of multiple selects.
Update all operands in that case and remove the assert. PR15805.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179982 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SROA.cpp

@@ -3051,16 +3051,16 @@ class AllocaPartitionRewriter : public InstVisitor<AllocaPartitionRewriter,
 
   bool visitSelectInst(SelectInst &SI) {
     DEBUG(dbgs() << "    original: " << SI << "\n");
-
-    // Find the operand we need to rewrite here.
-    bool IsTrueVal = SI.getTrueValue() == OldPtr;
-    if (IsTrueVal)
-      assert(SI.getFalseValue() != OldPtr && "Pointer is both operands!");
-    else
-      assert(SI.getFalseValue() == OldPtr && "Pointer isn't an operand!");
+    assert((SI.getTrueValue() == OldPtr || SI.getFalseValue() == OldPtr) &&
+           "Pointer isn't an operand!");
 
     Value *NewPtr = getAdjustedAllocaPtr(IRB, OldPtr->getType());
-    SI.setOperand(IsTrueVal ? 1 : 2, NewPtr);
+    // Replace the operands which were using the old pointer.
+    if (SI.getOperand(1) == OldPtr)
+      SI.setOperand(1, NewPtr);
+    if (SI.getOperand(2) == OldPtr)
+      SI.setOperand(2, NewPtr);
+
     DEBUG(dbgs() << "          to: " << SI << "\n");
     deleteIfTriviallyDead(OldPtr);
     return false;

test/Transforms/SROA/basictest.ll

@@ -1306,3 +1306,14 @@ end:
 ; CHECK: ret void
 }
 
+define void @PR15805(i1 %a, i1 %b) {
+; CHECK: @PR15805
+; CHECK: select i1 undef, i64* %c, i64* %c
+; CHECK: ret void
+
+  %c = alloca i64, align 8
+  %p.0.c = select i1 undef, i64* %c, i64* %c
+  %cond.in = select i1 undef, i64* %p.0.c, i64* %c
+  %cond = load i64* %cond.in, align 8
+  ret void
+}