[turbofan] Implementation of Word32PairShl on arm.

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
diff --git a/src/arm/macro-assembler-arm.cc b/src/arm/macro-assembler-arm.cc
index 80aef0c4ffefa253069de6ac66473a4ac116b2a4..936839e4eaf08cb2220d85db526d30bc17122bb7 100644
--- a/src/arm/macro-assembler-arm.cc
+++ b/src/arm/macro-assembler-arm.cc
@@ -1056,7 +1056,45 @@ void MacroAssembler::VmovLow(DwVfpRegister dst, Register src) {
     vmov(dst, VmovIndexLo, src);
   }
 }
+void MacroAssembler::PairLsl(Register dst_low, Register dst_high,
+                             Register src_low, Register src_high,
+                             Register scratch, Register shift) {
+  Label less_than_32;

[martyn.capewell, 2016/03/04 18:54:57]

Add some register alias assertions: perhaps !AreAliased() for all input
registers makes reasoning easier, but it may be helpful to allow dst_low ==
src_low and dst_high == src_high.

[ahaas, 2016/03/07 13:40:49]

I enforced src_low == dst_low now in the register allocator now, and I allow
src_high == dst_high.
I added !AreAliased() checks for (dst_low, src_high) and (dst_high, src_low).

+  Label done;
+  cmp_raw_immediate(shift, 32);
+  b(lt, &less_than_32);
+  eor(dst_low, dst_low, Operand(dst_low));

[martyn.capewell, 2016/03/04 18:54:57]

mov(dst_low, Operand(0))

[martyn.capewell, 2016/03/04 18:54:57]

Switching zero and shift operations here would allow dst_low to alias src_low.

[ahaas, 2016/03/07 13:40:48]

Done.

+  and_(scratch, shift, Operand(0x1f));
+  lsl(dst_high, src_low, Operand(scratch));
+  jmp(&done);
+  bind(&less_than_32);
+  rsb(scratch, shift, Operand(32));
+  lsr(dst_low, src_low, Operand(scratch));
+  lsl(dst_high, src_high, Operand(shift));
+  orr(dst_high, dst_high, dst_low);
+  lsl(dst_low, src_low, Operand(shift));

[martyn.capewell, 2016/03/04 18:54:57]

You can combine shift with orr here:
  lsl(dst_high, src_high, Operand(shift);
  orr(dst_high, dst_high, Operand(src_low, LSR, scratch));
  lsl(dst_low, src_low, Operand(shift));

[ahaas, 2016/03/07 13:40:48]

Thanks, that's really helpful.

+  bind(&done);
+}
 
+void MacroAssembler::PairLsl(Register dst_low, Register dst_high,
+                             Register src_low, Register src_high,
+                             Register scratch, uint32_t shift) {

[martyn.capewell, 2016/03/04 18:54:57]

scratch isn't used.

[ahaas, 2016/03/07 13:40:49]

I removed it.

+  Label less_than_32;

[martyn.capewell, 2016/03/04 18:54:57]

Add some register alias assertions. At the top level, I think (dst_low !=
dst_high) && (src_low != src_high) is enough.

[ahaas, 2016/03/07 13:40:49]

Done.

+  Label done;
+  if (shift >= 32) {

[martyn.capewell, 2016/03/04 18:54:57]

Switch the zero and shift instructions here, so dst_low can alias src_low.

[ahaas, 2016/03/07 13:40:49]

Done.

+    eor(dst_low, dst_low, Operand(dst_low));

[martyn.capewell, 2016/03/04 18:54:57]

mov(dst_low, Operand(0))

[ahaas, 2016/03/07 13:40:48]

Done.

+    shift &= 0x1f;
+    lsl(dst_high, src_low, Operand(shift));
+  } else if (shift == 0) {

[martyn.capewell, 2016/03/04 18:54:57]

Assert dst_low != src_high.

+    mov(dst_low, src_low);

[martyn.capewell, 2016/03/04 18:54:57]

Use Move() here to eliminate redundant instructions when dst == src.

[ahaas, 2016/03/07 13:40:49]

Aha, that's useful. Thanks.

+    mov(dst_high, src_high);
+  } else {
+    lsr(dst_low, src_low, Operand(32 - shift));
+    lsl(dst_high, src_high, Operand(shift));
+    orr(dst_high, dst_high, dst_low);
+    lsl(dst_low, src_low, Operand(shift));

[martyn.capewell, 2016/03/04 18:54:57]

Combine shift with orr:
  lsl(dst_high, src_high, Operand(shift);
  orr(dst_high, dst_high, Operand(src_low, LSR, 32 - shift));
  lsl(dst_low, src_low, Operand(shift));

Also, assert (dst_high != src_low) && (src_high != dst_low).

[ahaas, 2016/03/07 13:40:48]

Done.

+  }
+}
 
 void MacroAssembler::LoadConstantPoolPointerRegisterFromCodeTargetAddress(
     Register code_target_address) {