x64 support for d-to-i (truncated)

src/x64/code-stubs-x64.cc

Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index 0c0c2725cbf3e559c11c5a709985559ae3c4d528..ae0ad646e5984a95b4644a1dd71735df7691c8e1 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -607,71 +607,87 @@ class FloatingPointHelper : public AllStatic {
 };
 
 
-// Get the integer part of a heap number.
-// Overwrites the contents of rdi, rbx and rcx. Result cannot be rdi or rbx.
-void IntegerConvert(MacroAssembler* masm,
-                    Register result,
-                    Register source) {
-  // Result may be rcx. If result and source are the same register, source will
-  // be overwritten.
-  ASSERT(!result.is(rdi) && !result.is(rbx));
-  // TODO(lrn): When type info reaches here, if value is a 32-bit integer, use
-  // cvttsd2si (32-bit version) directly.
-  Register double_exponent = rbx;
-  Register double_value = rdi;
-  Label done, exponent_63_plus;
-  // Get double and extract exponent.
-  __ movq(double_value, FieldOperand(source, HeapNumber::kValueOffset));
-  // Clear result preemptively, in case we need to return zero.
-  __ xorl(result, result);
-  __ movq(xmm0, double_value);  // Save copy in xmm0 in case we need it there.
-  // Double to remove sign bit, shift exponent down to least significant bits.
-  // and subtract bias to get the unshifted, unbiased exponent.
-  __ lea(double_exponent, Operand(double_value, double_value, times_1, 0));
-  __ shr(double_exponent, Immediate(64 - HeapNumber::kExponentBits));
-  __ subl(double_exponent, Immediate(HeapNumber::kExponentBias));
-  // Check whether the exponent is too big for a 63 bit unsigned integer.
-  __ cmpl(double_exponent, Immediate(63));
-  __ j(above_equal, &exponent_63_plus, Label::kNear);
-  // Handle exponent range 0..62.
-  __ cvttsd2siq(result, xmm0);
-  __ jmp(&done, Label::kNear);
+void DoubleToIStub::Generate(MacroAssembler* masm) {
+    Register input_reg = this->source();
+    Register final_result_reg = this->destination();
+    ASSERT(is_truncating());
 
-  __ bind(&exponent_63_plus);
-  // Exponent negative or 63+.
-  __ cmpl(double_exponent, Immediate(83));
-  // If exponent negative or above 83, number contains no significant bits in
-  // the range 0..2^31, so result is zero, and rcx already holds zero.
-  __ j(above, &done, Label::kNear);
-
-  // Exponent in rage 63..83.
-  // Mantissa * 2^exponent contains bits in the range 2^0..2^31, namely
-  // the least significant exponent-52 bits.
-
-  // Negate low bits of mantissa if value is negative.
-  __ addq(double_value, double_value);  // Move sign bit to carry.
-  __ sbbl(result, result);  // And convert carry to -1 in result register.
-  // if scratch2 is negative, do (scratch2-1)^-1, otherwise (scratch2-0)^0.
-  __ addl(double_value, result);
-  // Do xor in opposite directions depending on where we want the result
-  // (depending on whether result is rcx or not).
-
-  if (result.is(rcx)) {
-    __ xorl(double_value, result);
-    // Left shift mantissa by (exponent - mantissabits - 1) to save the
-    // bits that have positional values below 2^32 (the extra -1 comes from the
-    // doubling done above to move the sign bit into the carry flag).
-    __ leal(rcx, Operand(double_exponent, -HeapNumber::kMantissaBits - 1));
-    __ shll_cl(double_value);
-    __ movl(result, double_value);
-  } else {
-    // As the then-branch, but move double-value to result before shifting.
-    __ xorl(result, double_value);
-    __ leal(rcx, Operand(double_exponent, -HeapNumber::kMantissaBits - 1));
-    __ shll_cl(result);
-  }
+    Label check_negative, process_64_bits, done;
 
-  __ bind(&done);
+    int double_offset = offset();
+
+    // Account for return address and saved regs if input is rsp.
+    if (input_reg.is(rsp)) double_offset += 3 * kPointerSize;
+
+    MemOperand mantissa_operand(MemOperand(input_reg, double_offset));
+    MemOperand exponent_operand(MemOperand(input_reg,
+                                           double_offset + kDoubleSize / 2));
+
+    Register scratch1;
+    Register scratch_candidates[3] = { rbx, rdx, rdi };
+    for (int i = 0; i < 3; i++) {
+      scratch1 = scratch_candidates[i];
+      if (!final_result_reg.is(scratch1) && !input_reg.is(scratch1)) break;
+    }
+
+    // Since we must use ecx for shifts below, use some other register (eax)
+    // to calculate the result if ecx is the requested return register.

[Yang, 2013/07/18 14:54:38]

comments do not apply to x64 registers

[danno, 2013/07/19 08:56:50]

Done.

+    Register result_reg = final_result_reg.is(rcx) ? rax : final_result_reg;
+    // Save ecx if it isn't the return register and therefore volatile, or if it
+    // is the return register, then save the temp register we use in its stead
+    // for the result.
+    Register save_reg = final_result_reg.is(rcx) ? rax : rcx;
+    __ push(scratch1);
+    __ push(save_reg);
+
+    bool stash_exponent_copy = !input_reg.is(rsp);
+    __ movl(scratch1, mantissa_operand);
+    __ movsd(xmm0, mantissa_operand);
+    __ movl(rcx, exponent_operand);
+    if (stash_exponent_copy) __ push(rcx);
+
+    __ andl(rcx, Immediate(HeapNumber::kExponentMask));
+    __ shrl(rcx, Immediate(HeapNumber::kExponentShift));
+    __ leal(result_reg, MemOperand(rcx, -HeapNumber::kExponentBias));
+    __ cmpl(result_reg, Immediate(HeapNumber::kMantissaBits));
+    __ j(below, &process_64_bits);
+
+    // Result is entirely in lower 32-bits of mantissa
+    int delta = HeapNumber::kExponentBias + Double::kPhysicalSignificandSize;
+    __ subl(rcx, Immediate(delta));
+    __ xorl(result_reg, result_reg);
+    __ cmpl(rcx, Immediate(31));
+    __ j(above, &done);
+    __ shll_cl(scratch1);
+    __ jmp(&check_negative);
+
+    __ bind(&process_64_bits);
+    __ cvttsd2siq(result_reg, xmm0);
+    __ jmp(&done, Label::kNear);
+
+    // If the double was negative, negate the integer result.
+    __ bind(&check_negative);
+    __ movl(result_reg, scratch1);
+    __ negl(result_reg);

[Yang, 2013/07/18 14:54:38]

We don't do zero-extension while moving anywhere. Could it happen that the upper
32-bit of the result just carries over?

[danno, 2013/07/19 08:56:50]

As discussed, on x64 we ignore the top 32-bits for most operations and
explicitly clear them before we need them if we do.

+    if (stash_exponent_copy) {
+        __ cmpl(MemOperand(rsp, 0), Immediate(0));
+    } else {
+        __ cmpl(exponent_operand, Immediate(0));
+    }
+    __ cmovl(greater, result_reg, scratch1);
+
+    // Restore registers
+    __ bind(&done);
+    if (stash_exponent_copy) {
+        __ addq(rsp, Immediate(kDoubleSize));
+    }
+    if (!final_result_reg.is(result_reg)) {
+        ASSERT(final_result_reg.is(rcx));
+        __ movl(final_result_reg, result_reg);
+    }
+    __ pop(save_reg);
+    __ pop(scratch1);
+    __ ret(0);
 }
 
 
@@ -1557,12 +1573,18 @@ void FloatingPointHelper::LoadNumbersAsIntegers(MacroAssembler* masm) {
   __ JumpIfSmi(rax, &rax_is_smi);
 
   __ bind(&rax_is_object);
-  IntegerConvert(masm, rcx, rax);  // Uses rdi, rcx and rbx.
+  DoubleToIStub stub1(rax, rcx, HeapNumber::kValueOffset - kHeapObjectTag,
+                     true);
+  __ call(stub1.GetCode(masm->isolate()), RelocInfo::CODE_TARGET);
+
   __ jmp(&done);
 
   __ bind(&rdx_is_object);
-  IntegerConvert(masm, rdx, rdx);  // Uses rdi, rcx and rbx.
+  DoubleToIStub stub2(rdx, rdx, HeapNumber::kValueOffset - kHeapObjectTag,
+                     true);
+  __ call(stub1.GetCode(masm->isolate()), RelocInfo::CODE_TARGET);
   __ JumpIfNotSmi(rax, &rax_is_object);
+
   __ bind(&rax_is_smi);
   __ SmiToInteger32(rcx, rax);
 
@@ -1597,7 +1619,9 @@ void FloatingPointHelper::LoadAsIntegers(MacroAssembler* masm,
   __ cmpq(FieldOperand(rdx, HeapObject::kMapOffset), heap_number_map);
   __ j(not_equal, &check_undefined_arg1);
   // Get the untagged integer version of the rdx heap number in rcx.
-  IntegerConvert(masm, r8, rdx);
+  DoubleToIStub stub1(rdx, r8, HeapNumber::kValueOffset - kHeapObjectTag,
+                      true);
+  __ call(stub1.GetCode(masm->isolate()), RelocInfo::CODE_TARGET);
 
   // Here r8 has the untagged integer, rax has a Smi or a heap number.
   __ bind(&load_arg2);
@@ -1617,7 +1641,10 @@ void FloatingPointHelper::LoadAsIntegers(MacroAssembler* masm,
   __ cmpq(FieldOperand(rax, HeapObject::kMapOffset), heap_number_map);
   __ j(not_equal, &check_undefined_arg2);
   // Get the untagged integer version of the rax heap number in rcx.
-  IntegerConvert(masm, rcx, rax);
+  DoubleToIStub stub2(rax, rcx, HeapNumber::kValueOffset - kHeapObjectTag,
+                      true);
+  __ call(stub2.GetCode(masm->isolate()), RelocInfo::CODE_TARGET);
+
   __ bind(&done);
   __ movl(rax, r8);
 }