[ARM] Delete duplicate known bits implementation for ARMISD::CMOV.

[efriedma]

Summary

Not only is it useless, it's wrong: it doesn't check the correct operands.

(See ARMTargetLowering::computeKnownBitsForTargetNode for the other implementation.)

Fixes https://bugs.llvm.org//show_bug.cgi?id=32379 .

[jmolloy]

Looks even better than Pirama's patch. Thanks!

sidenote: I know I added *one* of these... now I'm wondering if I added the correct or broken one and how there ended up being two!

[efriedma]

The correctness fix was already merged; I'll submit the cleanup separately.

lib/Target/ARM/ARMISelLowering.cpp

if (Op.getOpcode() == ARMISD::BFI) {
     // The operand to BFI is already a mask suitable for removing the bits it
     // sets.
     ConstantSDNode *CI = cast<ConstantSDNode>(Op.getOperand(2));
     const APInt &Mask = CI->getAPIntValue();
     KnownZero &= Mask;
     KnownOne &= Mask;
     return;
   }
-  if (Op.getOpcode() == ARMISD::CMOV) {
-    APInt KZ2(KnownZero.getBitWidth(), 0);
-    APInt KO2(KnownOne.getBitWidth(), 0);
-    computeKnownBits(DAG, Op.getOperand(1), KnownZero, KnownOne);
-    computeKnownBits(DAG, Op.getOperand(2), KZ2, KO2);
-
-    KnownZero &= KZ2;
-    KnownOne &= KO2;
-    return;
-  }
   return DAG.computeKnownBits(Op, KnownZero, KnownOne);
 }
 
 SDValue ARMTargetLowering::PerformCMOVToBFICombine(SDNode *CMOV, SelectionDAG &DAG) const {
   // If we have a CMOV, OR and AND combination such as:
   //   if (x & CN)
   //     y |= CM;
   //

test/CodeGen/ARM/bfi.ll

 ; CHECK-NOT: bfi
   %y2 = and i32 %y, 4294967040 ; 0xFFFFFF00
   %and = and i32 %x, 4
   %or = or i32 %y2, 16
   %cmp = icmp eq i32 %and, 42 ; Not comparing against zero!
   %sel = select i1 %cmp, i32 %y2, i32 %or
   ret i32 %sel
 }
+
+; (We could probably improve the generated code here by converting the
+; or + select sequence into "orr r0, r0, r3, lsl #1" or something like that.)
+define i64 @f14(i64 %data, i1 zeroext %f1, i1 zeroext %f2) local_unnamed_addr #0 {
+; CHECK-LABEL: f14:
+; CHECK: cmp r2, #0
+; CHECK-NEXT: bfc [[RESULT:r[0-9]+]], #1, #1
+; CHECK-NEXT: moveq [[RESULT]], r0
+; CHECK-NEXT: cmp r3, #0
+; CHECK-NEXT: orrne [[RESULT:r[0-9]+]], [[RESULT]], #2
+  %and = and i64 %data, -3
+  %and.data = select i1 %f1, i64 %and, i64 %data
+  %or = or i64 %and.data, 2
+  %data.addr.1 = select i1 %f2, i64 %or, i64 %and.data
+  ret i64 %data.addr.1
+}