[ARM] CMOV->BFI combining: handle both senses of CMPZ

I completely misunderstood what ARMISD::CMPZ means. It's not "compare equal to zero", it's "compare, only setting the zero/Z flag". It can either be equal-to-zero or not-equal-to-zero, and we weren't checking what sense it was.

If it's equal-to-zero, we can swap the operands around and pretend like it is not-equal-to-zero, which is both a bug fix and lets us handle more cases.

llvm-svn: 252891

2 files changed, 21 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 87bd9be01f0..8316f889e57 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -10393,6 +10393,8 @@ SDValue ARMTargetLowering::PerformCMOVToBFICombine(SDNode *CMOV, SelectionDAG &D
 
   SDValue Op0 = CMOV->getOperand(0);
   SDValue Op1 = CMOV->getOperand(1);
+  auto CCNode = cast<ConstantSDNode>(CMOV->getOperand(2));
+  auto CC = CCNode->getAPIntValue().getLimitedValue();
   SDValue CmpZ = CMOV->getOperand(4);
 
   assert(CmpZ->getOpcode() == ARMISD::CMPZ);
@@ -10404,6 +10406,14 @@ SDValue ARMTargetLowering::PerformCMOVToBFICombine(SDNode *CMOV, SelectionDAG &D
     return SDValue();
   SDValue X = And->getOperand(0);
 
+  if (CC == ARMCC::EQ) {
+    // We're performing an "equal to zero" compare. Swap the operands so we
+    // canonicalize on a "not equal to zero" compare.
+    std::swap(Op0, Op1);
+  } else {
+    assert(CC == ARMCC::NE && "How can a CMPZ node not be EQ or NE?");
+  }
+  
   if (Op1->getOpcode() != ISD::OR)
     return SDValue();
 
diff --git a/llvm/test/CodeGen/ARM/bfi.ll b/llvm/test/CodeGen/ARM/bfi.ll
index 7699527420a..39bcbf2cfec 100644
--- a/llvm/test/CodeGen/ARM/bfi.ll
+++ b/llvm/test/CodeGen/ARM/bfi.ll
@@ -147,3 +147,14 @@ define i32 @f11(i32 %x, i32 %y) {
 
   ret i32 %bsel
 }
+
+define i32 @f12(i32 %x, i32 %y) {
+; CHECK-LABEL: f12:
+; CHECK: bfi r1, r0, #4, #1
+  %y2 = and i32 %y, 4294967040 ; 0xFFFFFF00
+  %and = and i32 %x, 4
+  %or = or i32 %y2, 16
+  %cmp = icmp eq i32 %and, 0
+  %sel = select i1 %cmp, i32 %y2, i32 %or
+  ret i32 %sel
+}