[SystemZ] Bugfix in adjustSubwordCmp.

Csmith generated a program where a store after load to the same address did
not get chained after the new load created during DAG legalizing, and so
performed an illegal overwrite of the expected value.

When the new zero-extending load is created, the chain users of the original
load must be updated, which was not done previously.

A similar case was also found and handled in lowerBITCAST.

Review: Ulrich Weigand
https://reviews.llvm.org/D40542

llvm-svn: 319409

1 files changed, 11 insertions, 4 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
index d49d7316e68..ad14e5e34e2 100644
--- a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -1844,11 +1844,14 @@ static void adjustSubwordCmp(SelectionDAG &DAG, const SDLoc &DL,
                               ISD::SEXTLOAD :
                               ISD::ZEXTLOAD);
   if (C.Op0.getValueType() != MVT::i32 ||
-      Load->getExtensionType() != ExtType)
+      Load->getExtensionType() != ExtType) {
     C.Op0 = DAG.getExtLoad(ExtType, SDLoc(Load), MVT::i32, Load->getChain(),
                            Load->getBasePtr(), Load->getPointerInfo(),
                            Load->getMemoryVT(), Load->getAlignment(),
                            Load->getMemOperand()->getFlags());
+    // Update the chain uses.
+    DAG.ReplaceAllUsesOfValueWith(SDValue(Load, 1), C.Op0.getValue(1));
+  }
 
   // Make sure that the second operand is an i32 with the right value.
   if (C.Op1.getValueType() != MVT::i32 ||
@@ -2940,9 +2943,13 @@ SDValue SystemZTargetLowering::lowerBITCAST(SDValue Op,
   // but we need this case for bitcasts that are created during lowering
   // and which are then lowered themselves.
   if (auto *LoadN = dyn_cast<LoadSDNode>(In))
-    if (ISD::isNormalLoad(LoadN))
-      return DAG.getLoad(ResVT, DL, LoadN->getChain(), LoadN->getBasePtr(),
-                         LoadN->getMemOperand());
+    if (ISD::isNormalLoad(LoadN)) {
+      SDValue NewLoad = DAG.getLoad(ResVT, DL, LoadN->getChain(),
+                                    LoadN->getBasePtr(), LoadN->getMemOperand());
+      // Update the chain uses.
+      DAG.ReplaceAllUsesOfValueWith(SDValue(LoadN, 1), NewLoad.getValue(1));
+      return NewLoad;
+    }
 
   if (InVT == MVT::i32 && ResVT == MVT::f32) {
     SDValue In64;