[DAG] Teach BaseIndexOffset to correctly handle with indexed operations

BaseIndexOffset address analysis incorrectly ignores offsets folded
into indexed memory operations causing potential errors in alias
analysis of pre-indexed operations.

Reviewers: efriedma, RKSimon, hfinkel, jyknight

Subscribers: hiraditya, javed.absar, llvm-commits

Differential Revision: https://reviews.llvm.org/D41701

llvm-svn: 322003

1 files changed, 20 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp
index d5980919d03..da1574f6052 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp
@@ -21,6 +21,9 @@ using namespace llvm;
 
 bool BaseIndexOffset::equalBaseIndex(BaseIndexOffset &Other,
                                      const SelectionDAG &DAG, int64_t &Off) {
+  // Conservatively fail if we a match failed..
+  if (!Base.getNode() || !Other.Base.getNode())
+    return false;
   // Initial Offset difference.
   Off = Other.Offset - Offset;
 
@@ -72,13 +75,29 @@ bool BaseIndexOffset::equalBaseIndex(BaseIndexOffset &Other,
 }
 
 /// Parses tree in Ptr for base, index, offset addresses.
-BaseIndexOffset BaseIndexOffset::match(SDValue Ptr, const SelectionDAG &DAG) {
+BaseIndexOffset BaseIndexOffset::match(LSBaseSDNode *N,
+                                       const SelectionDAG &DAG) {
+  SDValue Ptr = N->getBasePtr();
+
   // (((B + I*M) + c)) + c ...
   SDValue Base = DAG.getTargetLoweringInfo().unwrapAddress(Ptr);
   SDValue Index = SDValue();
   int64_t Offset = 0;
   bool IsIndexSignExt = false;
 
+  // pre-inc/pre-dec ops are components of EA.
+  if (N->getAddressingMode() == ISD::PRE_INC) {
+    if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset()))
+      Offset += C->getSExtValue();
+    else // If unknown, give up now.
+      return BaseIndexOffset(SDValue(), SDValue(), 0, false);
+  } else if (N->getAddressingMode() == ISD::PRE_DEC) {
+    if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset()))
+      Offset -= C->getSExtValue();
+    else // If unknown, give up now.
+      return BaseIndexOffset(SDValue(), SDValue(), 0, false);
+  }
+
   // Consume constant adds & ors with appropriate masking.
   while (Base->getOpcode() == ISD::ADD || Base->getOpcode() == ISD::OR) {
     if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1))) {