Revert "[X86] Don't exit from foldOffsetIntoAddress if the Offset is 0, but AM.Disp is non-zero."

Possibly causing build bot failures.

Author: topperc

llvm/lib/Target/X86/X86ISelDAGToDAG.cpp

@@ -1409,17 +1409,15 @@ static bool isDispSafeForFrameIndex(int64_t Val) {
 
 bool X86DAGToDAGISel::foldOffsetIntoAddress(uint64_t Offset,
                                             X86ISelAddressMode &AM) {
-  // If the final displacement is 0, we don't need to do any work. We may have
-  // already matched a displacement and the caller just added the symbolic
-  // displacement with an offset of 0. So recheck everything if Val is non-zero.
-  int64_t Val = AM.Disp + Offset;
-  if (Val == 0)
+  // If there's no offset to fold, we don't need to do any work.
+  if (Offset == 0)
     return false;
 
   // Cannot combine ExternalSymbol displacements with integer offsets.
   if (AM.ES || AM.MCSym)
     return true;
 
+  int64_t Val = AM.Disp + Offset;
   CodeModel::Model M = TM.getCodeModel();
   if (Subtarget->is64Bit()) {
     if (!X86::isOffsetSuitableForCodeModel(Val, M,
@@ -1583,13 +1581,24 @@ bool X86DAGToDAGISel::matchAdd(SDValue &N, X86ISelAddressMode &AM,
   if (!matchAddressRecursively(N.getOperand(0), AM, Depth+1) &&
       !matchAddressRecursively(Handle.getValue().getOperand(1), AM, Depth+1))
     return false;
-  AM = Backup;
 
-  // Try again after commutating the operands.
-  if (!matchAddressRecursively(Handle.getValue().getOperand(1), AM,
-                               Depth + 1) &&
-      !matchAddressRecursively(Handle.getValue().getOperand(0), AM, Depth + 1))
-    return false;
+  // Don't try commuting operands if the address is in the form of
+  // sym+disp(%rip). foldOffsetIntoAddress() currently does not know there is a
+  // symbolic displacement and would fold disp. If disp is just a bit smaller
+  // than 2**31, it can easily cause a relocation overflow.
+  bool NoCommutate = false;
+  if (AM.isRIPRelative() && AM.hasSymbolicDisplacement())
+    if (ConstantSDNode *Cst =
+            dyn_cast<ConstantSDNode>(Handle.getValue().getOperand(1)))
+      NoCommutate = Cst->getSExtValue() != 0;
+
+  AM = Backup;
+  if (!NoCommutate) {
+    // Try again after commutating the operands.
+    if (!matchAddressRecursively(Handle.getValue().getOperand(1), AM, Depth + 1) &&
+        !matchAddressRecursively(Handle.getValue().getOperand(0), AM, Depth + 1))
+      return false;
+  }
   AM = Backup;
 
   // If we couldn't fold both operands into the address at the same time,