[X86] Teach DAG unfoldMemoryOperand to reconvert CMPs to tests

Summary:
Copy MI-level cmp->test conversion to SelectionDAG-level memory unfold.
This fixes a regression from upcoming D41293 change.

Reviewers: craig.topper, RKSimon

Reviewed By: craig.topper

Subscribers: llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D42808

llvm-svn: 324261

1 files changed, 24 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index 9c6c8600745..77310f0f06b 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -9223,6 +9223,30 @@ X86InstrInfo::unfoldMemoryOperand(SelectionDAG &DAG, SDNode *N,
   if (Load)
     BeforeOps.push_back(SDValue(Load, 0));
   BeforeOps.insert(BeforeOps.end(), AfterOps.begin(), AfterOps.end());
+  // Change CMP32ri r, 0 back to TEST32rr r, r, etc.
+  switch (Opc) {
+    default: break;
+    case X86::CMP64ri32:
+    case X86::CMP64ri8:
+    case X86::CMP32ri:
+    case X86::CMP32ri8:
+    case X86::CMP16ri:
+    case X86::CMP16ri8:
+    case X86::CMP8ri:
+      if (isNullConstant(BeforeOps[1])) {
+        switch (Opc) {
+          default: llvm_unreachable("Unreachable!");
+          case X86::CMP64ri8:
+          case X86::CMP64ri32: Opc = X86::TEST64rr; break;
+          case X86::CMP32ri8:
+          case X86::CMP32ri:   Opc = X86::TEST32rr; break;
+          case X86::CMP16ri8:
+          case X86::CMP16ri:   Opc = X86::TEST16rr; break;
+          case X86::CMP8ri:    Opc = X86::TEST8rr; break;
+        }
+        BeforeOps[1] = BeforeOps[0];
+      }
+  }
   SDNode *NewNode= DAG.getMachineNode(Opc, dl, VTs, BeforeOps);
   NewNodes.push_back(NewNode);