MIPS: Followup '[turbofan] Introduce new operators Float32SubPreserveNan and Float64SubPreserveNan'.

src/mips/macro-assembler-mips.cc

Index: src/mips/macro-assembler-mips.cc
diff --git a/src/mips/macro-assembler-mips.cc b/src/mips/macro-assembler-mips.cc
index a58084cfbef4f76a98e8ce55691b7ba81ba77175..2688c46b16ea136c574cd9c92aa7961fa278158d 100644
--- a/src/mips/macro-assembler-mips.cc
+++ b/src/mips/macro-assembler-mips.cc
@@ -18,6 +18,17 @@
 namespace v8 {
 namespace internal {
 
+// Floating point constants.
+const uint32_t kDoubleExponentShift = HeapNumber::kExponentShift;
+const uint32_t kDoubleNaNShift = kDoubleExponentShift - 1;
+const uint32_t kDoubleNaNMask =
+    HeapNumber::kExponentMask | (1 << kDoubleNaNShift);
+
+const uint32_t kSingleExponentMask = kBinary32ExponentMask;
+const uint32_t kSingleExponentShift = kBinary32ExponentShift;
+const uint32_t kSingleNaNShift = kSingleExponentShift - 1;
+const uint32_t kSingleNaNMask = kSingleExponentMask | (1 << kSingleNaNShift);
+
 MacroAssembler::MacroAssembler(Isolate* arg_isolate, void* buffer, int size,
                                CodeObjectRequired create_code_object)
     : Assembler(arg_isolate, buffer, size),
@@ -4715,6 +4726,72 @@ void MacroAssembler::StoreNumberToDoubleElements(Register value_reg,
   bind(&done);
 }
 
+void MacroAssembler::SubNanPreservePayloadAndSign_s(FloatRegister fd,
+                                                    FloatRegister fs,
+                                                    FloatRegister ft) {
+  FloatRegister dest = fd.is(fs) || fd.is(ft) ? kLithiumScratchDouble : fd;
+  Label check_nan, save_payload, done;
+  Register scratch1 = t8;
+  Register scratch2 = t9;
+
+  sub_s(dest, fs, ft);
+  // Check if the result of subtraction is NaN.
+  BranchF32(nullptr, &check_nan, eq, fs, ft);
+  Branch(USE_DELAY_SLOT, &done);
+  dest.is(fd) ? nop() : mov_s(fd, dest);
+
+  bind(&check_nan);
+  // Check if first operand is a NaN.
+  mfc1(scratch1, fs);
+  BranchF32(nullptr, &save_payload, eq, fs, fs);
+  // Second operand must be a NaN.
+  mfc1(scratch1, ft);
+
+  bind(&save_payload);
+  // Reserve payload.
+  And(scratch1, scratch1, Operand((1 << kSingleNaNShift) - 1));
+  mfc1(scratch2, dest);
+  And(scratch2, scratch2, Operand(kSingleNaNMask));

[Marija Antic, 2016/06/16 11:25:26]

This will set the sign bit to 0 (ci20 board was changing the sign of the NaN
when subtracting from -0). Have you checked what happens with the negative NaN
input?

[balazs.kilvady, 2016/06/16 12:00:03]

Yes. The test expects + quiet NaN with payload (Intel behavior?). So that is why
I clear the sign bit here.

+  Or(scratch2, scratch2, scratch1);
+  mtc1(scratch2, fd);
+
+  bind(&done);
+}
+
+void MacroAssembler::SubNanPreservePayloadAndSign_d(DoubleRegister fd,
+                                                    DoubleRegister fs,
+                                                    DoubleRegister ft) {
+  FloatRegister dest = fd.is(fs) || fd.is(ft) ? kLithiumScratchDouble : fd;
+  Label check_nan, save_payload, done;
+  Register scratch1 = t8;
+  Register scratch2 = t9;
+
+  sub_d(dest, fs, ft);
+  // Check if the result of subtraction is NaN.
+  BranchF64(nullptr, &check_nan, eq, fs, ft);
+  Branch(USE_DELAY_SLOT, &done);
+  dest.is(fd) ? nop() : mov_d(fd, dest);
+
+  bind(&check_nan);
+  // Check if first operand is a NaN.
+  Mfhc1(scratch1, fs);
+  mov_s(dest, fs);
+  BranchF64(nullptr, &save_payload, eq, fs, fs);
+  // Second operand must be a NaN.
+  Mfhc1(scratch1, ft);
+  mov_s(dest, ft);
+
+  bind(&save_payload);
+  // Reserve payload.
+  And(scratch1, scratch1, Operand((1 << (kDoubleNaNShift)) - 1));
+  Mfhc1(scratch2, dest);
+  And(scratch2, scratch2, Operand(kDoubleNaNMask));
+  Or(scratch2, scratch2, scratch1);
+  Move_s(fd, dest);
+  Mthc1(scratch2, fd);
+
+  bind(&done);
+}
 
 void MacroAssembler::CompareMapAndBranch(Register obj,
                                          Register scratch,