Revert r291640 change to fold X86 comparison with atomic_load_add.

Even with the fix from r291630, this still causes problems. I get
widespread assertion failures in the Swift runtime's WeakRefCount::increment()
function. I sent a reduced testcase in reply to the commit.

llvm-svn: 292242

1 files changed, 10 insertions, 22 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index cef3bff622c..8c531f42179 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -29515,19 +29515,11 @@ static SDValue combineSelect(SDNode *N, SelectionDAG &DAG,
   return SDValue();
 }
 
-/// Combine brcond/cmov/setcc/.. based on comparing the result of
-/// atomic_load_add to use EFLAGS produced by the addition
-/// directly if possible. For example:
-///
-///   (setcc (cmp (atomic_load_add x, -C) C), COND_E)
-/// becomes:
-///   (setcc (LADD x, -C), COND_E)
-///
-/// and
+/// Combine:
 ///   (brcond/cmov/setcc .., (cmp (atomic_load_add x, 1), 0), COND_S)
-/// becomes:
+/// to:
 ///   (brcond/cmov/setcc .., (LADD x, 1), COND_LE)
-///
+/// i.e., reusing the EFLAGS produced by the LOCKed instruction.
 /// Note that this is only legal for some op/cc combinations.
 static SDValue combineSetCCAtomicArith(SDValue Cmp, X86::CondCode &CC,
                                        SelectionDAG &DAG) {
@@ -29542,7 +29534,7 @@ static SDValue combineSetCCAtomicArith(SDValue Cmp, X86::CondCode &CC,
   if (!Cmp.hasOneUse())
     return SDValue();
 
-  // This applies to variations of the common case:
+  // This only applies to variations of the common case:
   //   (icmp slt x, 0) -> (icmp sle (add x, 1), 0)
   //   (icmp sge x, 0) -> (icmp sgt (add x, 1), 0)
   //   (icmp sle x, 0) -> (icmp slt (sub x, 1), 0)
@@ -29561,9 +29553,8 @@ static SDValue combineSetCCAtomicArith(SDValue Cmp, X86::CondCode &CC,
     return SDValue();
 
   auto *CmpRHSC = dyn_cast<ConstantSDNode>(CmpRHS);
-  if (!CmpRHSC)
+  if (!CmpRHSC || CmpRHSC->getZExtValue() != 0)
     return SDValue();
-  APInt Comparand = CmpRHSC->getAPIntValue();
 
   const unsigned Opc = CmpLHS.getOpcode();
 
@@ -29579,19 +29570,16 @@ static SDValue combineSetCCAtomicArith(SDValue Cmp, X86::CondCode &CC,
   if (Opc == ISD::ATOMIC_LOAD_SUB)
     Addend = -Addend;
 
-  if (Comparand == -Addend) {
-    // No change to CC.
-  } else if (CC == X86::COND_S && Comparand == 0 && Addend == 1) {
+  if (CC == X86::COND_S && Addend == 1)
     CC = X86::COND_LE;
-  } else if (CC == X86::COND_NS && Comparand == 0 && Addend == 1) {
+  else if (CC == X86::COND_NS && Addend == 1)
     CC = X86::COND_G;
-  } else if (CC == X86::COND_G && Comparand == 0 && Addend == -1) {
+  else if (CC == X86::COND_G && Addend == -1)
     CC = X86::COND_GE;
-  } else if (CC == X86::COND_LE && Comparand == 0 && Addend == -1) {
+  else if (CC == X86::COND_LE && Addend == -1)
     CC = X86::COND_L;
-  } else {
+  else
     return SDValue();
-  }
 
   SDValue LockOp = lowerAtomicArithWithLOCK(CmpLHS, DAG);
   DAG.ReplaceAllUsesOfValueWith(CmpLHS.getValue(0),