[X86] Teach -Os immediate sharing code to not count constant uses that will become INC/DEC.

INC/DEC don't use an immediate so we don't need to count it. We
also shouldn't use the custom isel for it.

Fixes PR42998.

llvm-svn: 369863

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
index 46886419421..e0a462471a7 100644
--- a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -362,6 +362,11 @@ namespace {
         if (User->getNumOperands() != 2)
           continue;
 
+        // If this can match to INC/DEC, don't count it as a use.
+        if (User->getOpcode() == ISD::ADD &&
+            (isOneConstant(SDValue(N, 0)) || isAllOnesConstant(SDValue(N, 0))))
+          continue;
+
         // Immediates that are used for offsets as part of stack
         // manipulation should be left alone. These are typically
         // used to indicate SP offsets for argument passing and
@@ -4369,6 +4374,10 @@ void X86DAGToDAGISel::Select(SDNode *Node) {
     if (!isInt<8>(Val) && !isInt<32>(Val))
       break;
 
+    // If this can match to INC/DEC, let it go.
+    if (Opcode == ISD::ADD && (Val == 1 || Val == -1))
+      break;
+
     // Check if we should avoid folding this immediate.
     if (!shouldAvoidImmediateInstFormsForSize(N1.getNode()))
       break;