Merge pull request #2042 from cfallin/aarch64-fix-regshift-mask

Aarch64: mask shift-amounts incorporated into reg-reg-shift ALU insts.

cranelift/codegen/src/isa/aarch64/inst/args.rs

@@ -52,6 +52,11 @@ impl ShiftOpShiftImm {
     pub fn value(self) -> u8 {
         self.0
     }
+
+    /// Mask down to a given number of bits.
+    pub fn mask(self, bits: u8) -> ShiftOpShiftImm {
+        ShiftOpShiftImm(self.0 & (bits - 1))
+    }
 }
 
 /// A shift operator with an amount, guaranteed to be within range.

cranelift/codegen/src/isa/aarch64/lower.rs

@@ -321,8 +321,12 @@ fn put_input_in_rs<C: LowerCtx<I = Inst>>(
 
             // Can we get the shift amount as an immediate?
             if let Some(shiftimm) = input_to_shiftimm(ctx, shift_amt) {
-                let reg = put_input_in_reg(ctx, shiftee, narrow_mode);
-                return ResultRS::RegShift(reg, ShiftOpAndAmt::new(ShiftOp::LSL, shiftimm));
+                let shiftee_bits = ty_bits(ctx.input_ty(insn, 0));
+                if shiftee_bits <= u8::MAX as usize {
+                    let shiftimm = shiftimm.mask(shiftee_bits as u8);
+                    let reg = put_input_in_reg(ctx, shiftee, narrow_mode);
+                    return ResultRS::RegShift(reg, ShiftOpAndAmt::new(ShiftOp::LSL, shiftimm));
+                }
             }
         }
     }

cranelift/filetests/filetests/vcode/aarch64/arithmetic.clif

@@ -365,3 +365,18 @@ block0(v0: i64, v1: i64):
 ; nextln:  mov sp, fp
 ; nextln:  ldp fp, lr, [sp], #16
 ; nextln:  ret
+
+function %f25(i32, i32) -> i32 {
+block0(v0: i32, v1: i32):
+  v2 = iconst.i32 53
+  v3 = ishl.i32 v0, v2
+  v4 = isub.i32 v1, v3
+  return v4
+}
+
+; check:  stp fp, lr, [sp, #-16]!
+; nextln:  mov fp, sp
+; nextln:  sub w0, w1, w0, LSL 21
+; nextln:  mov sp, fp
+; nextln:  ldp fp, lr, [sp], #16
+; nextln:  ret