Fix bug 25440: GVN assertion after coercing loads

Optimizations like LoadPRE in GVN will insert new instructions.
If the insertion point is in a already processed BB, they should
get a value number explicitly. If the insertion point is after
current instruction, then just leave it. However, current GVN framework
has no support for it.
In this patch, we just bail out if a VN can't be found.

Dfferential Revision: http://reviews.llvm.org/D14670

A    test/Transforms/GVN/pr25440.ll
M    lib/Transforms/Scalar/GVN.cpp

llvm-svn: 253536

1 files changed, 12 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index 1cb7198e9ee..1f9630ed511 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -129,6 +129,7 @@ namespace {
     uint32_t lookup(Value *V) const;
     uint32_t lookup_or_add_cmp(unsigned Opcode, CmpInst::Predicate Pred,
                                Value *LHS, Value *RHS);
+    bool exists(Value *V) const;
     void add(Value *V, uint32_t num);
     void clear();
     void erase(Value *v);
@@ -389,6 +390,9 @@ uint32_t ValueTable::lookup_or_add_call(CallInst *C) {
   }
 }
 
+/// Returns true if a value number exists for the specified value.
+bool ValueTable::exists(Value *V) const { return valueNumbering.count(V) != 0; }
+
 /// lookup_or_add - Returns the value number for the specified value, assigning
 /// it a new number if it did not have one before.
 uint32_t ValueTable::lookup_or_add(Value *V) {
@@ -2534,7 +2538,14 @@ bool GVN::performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred,
     Value *Op = Instr->getOperand(i);
     if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
       continue;
-
+    // This could be a newly inserted instruction, in which case, we won't
+    // find a value number, and should give up before we hurt ourselves.
+    // FIXME: Rewrite the infrastructure to let it easier to value number
+    // and process newly inserted instructions.
+    if (!VN.exists(Op)) {
+      success = false;
+      break;
+    }
     if (Value *V = findLeader(Pred, VN.lookup(Op))) {
       Instr->setOperand(i, V);
     } else {