[liftoff][arm] Implement Copy Sign

This implements copy sign for both the arm32 and arm64 port of Liftoff.

Bug: v8:6600
Change-Id: Ic822e75417c6b911a03e8e9a2d6d59a98fbc3d18
Reviewed-on: https://chromium-review.googlesource.com/c/1348430
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57843}

src/wasm/baseline/arm/liftoff-assembler-arm.h

@@ -626,7 +626,6 @@ UNIMPLEMENTED_FP_UNOP(f32_floor)
 UNIMPLEMENTED_FP_UNOP(f32_trunc)
 UNIMPLEMENTED_FP_UNOP(f32_nearest_int)
 UNIMPLEMENTED_FP_UNOP(f32_sqrt)
-UNIMPLEMENTED_FP_BINOP(f64_copysign)
 FP64_BINOP(f64_add, vadd)
 FP64_BINOP(f64_sub, vsub)
 FP64_BINOP(f64_mul, vmul)
@@ -847,6 +846,26 @@ void LiftoffAssembler::emit_i32_to_intptr(Register dst, Register src) {
   // This is a nop on arm.
 }
 
+void LiftoffAssembler::emit_f64_copysign(DoubleRegister dst, DoubleRegister lhs,
+                                         DoubleRegister rhs) {
+  constexpr uint32_t kF64SignBitHighWord = uint32_t{1} << 31;
+  // On arm, we cannot hold the whole f64 value in a gp register, so we just
+  // operate on the upper half (UH).
+  UseScratchRegisterScope temps(this);
+  Register scratch = temps.Acquire();
+  Register scratch2 = GetUnusedRegister(kGpReg).gp();
+  VmovHigh(scratch, lhs);
+  // Clear sign bit in {scratch}.
+  bic(scratch, scratch, Operand(kF64SignBitHighWord));
+  VmovHigh(scratch2, rhs);
+  // Isolate sign bit in {scratch2}.
+  and_(scratch2, scratch2, Operand(kF64SignBitHighWord));
+  // Combine {scratch2} into {scratch}.
+  orr(scratch, scratch, scratch2);
+  vmov(dst, lhs);
+  VmovHigh(dst, scratch);
+}
+
 bool LiftoffAssembler::emit_type_conversion(WasmOpcode opcode,
                                             LiftoffRegister dst,
                                             LiftoffRegister src, Label* trap) {

src/wasm/baseline/arm64/liftoff-assembler-arm64.h

@@ -628,12 +628,24 @@ void LiftoffAssembler::emit_i32_to_intptr(Register dst, Register src) {
 
 void LiftoffAssembler::emit_f32_copysign(DoubleRegister dst, DoubleRegister lhs,
                                          DoubleRegister rhs) {
-  BAILOUT("f32_copysign");
+  UseScratchRegisterScope temps(this);
+  DoubleRegister scratch = temps.AcquireD();
+  Ushr(scratch.V2S(), rhs.V2S(), 31);
+  if (dst != lhs) {
+    Fmov(dst.S(), lhs.S());
+  }
+  Sli(dst.V2S(), scratch.V2S(), 31);
 }
 
 void LiftoffAssembler::emit_f64_copysign(DoubleRegister dst, DoubleRegister lhs,
                                          DoubleRegister rhs) {
-  BAILOUT("f64_copysign");
+  UseScratchRegisterScope temps(this);
+  DoubleRegister scratch = temps.AcquireD();
+  Ushr(scratch.V1D(), rhs.V1D(), 63);
+  if (dst != lhs) {
+    Fmov(dst.D(), lhs.D());
+  }
+  Sli(dst.V1D(), scratch.V1D(), 63);
 }
 
 bool LiftoffAssembler::emit_type_conversion(WasmOpcode opcode,