[Thumb] Resolve FIXME: Transform "(and (shl x, c2), c1)" into "(shl (and x, c1>>c2), c2)" (llvm#82120)

Transform "(and (shl x, c2), c1)" into "(shl (and x, c1>>c2), c2)" if
"c1 >> c2" is a cheaper immediate than "c1" using
HasLowerConstantMaterializationCost

Author: AZero13

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -14381,9 +14381,17 @@ static SDValue CombineANDShift(SDNode *N,
     }
   }
 
-  // FIXME: Transform "(and (shl x, c2) c1)" ->
-  // "(shl (and x, c1>>c2), c2)" if "c1 >> c2" is a cheaper immediate than
-  // c1.
+  // Transform "(and (shl x, c2) c1)" into "(shl (and x, c1>>c2), c2)"
+  // if "c1 >> c2" is a cheaper immediate than "c1"
+  if (LeftShift &&
+      HasLowerConstantMaterializationCost(C1 >> C2, C1, Subtarget)) {
+
+    SDValue And = DAG.getNode(ISD::AND, DL, MVT::i32, N0->getOperand(0),
+                              DAG.getConstant(C1 >> C2, DL, MVT::i32));
+    return DAG.getNode(ISD::SHL, DL, MVT::i32, And,
+                       DAG.getConstant(C2, DL, MVT::i32));
+  }
+
   return SDValue();
 }
 

llvm/test/CodeGen/Thumb/shift-and.ll

@@ -70,9 +70,8 @@ define i32 @test6(i32 %x) {
 ; CHECK-LABEL: test6:
 ; CHECK:       @ %bb.0: @ %entry
 ; CHECK-NEXT:    movs r1, #5
-; CHECK-NEXT:    lsls r1, r1, #29
-; CHECK-NEXT:    lsls r0, r0, #29
-; CHECK-NEXT:    ands r0, r1
+; CHECK-NEXT:    ands r1, r0
+; CHECK-NEXT:    lsls r0, r1, #29
 ; CHECK-NEXT:    bx lr
 entry:
   %0 = shl i32 %x, 29