uint64_t imm,
int shift,
MoveWideImmediateOp mov_op) {
- // Ignore the top 32 bits of an immediate if we're moving to a W register.
- if (rd.Is32Bits()) {
- // Check that the top 32 bits are zero (a positive 32-bit number) or top
- // 33 bits are one (a negative 32-bit number, sign extended to 64 bits).
- ASSERT(((imm >> kWRegSizeInBits) == 0) ||
- ((imm >> (kWRegSizeInBits - 1)) == 0x1ffffffff));
- imm &= kWRegMask;
- }
-
if (shift >= 0) {
// Explicit shift specified.
ASSERT((shift == 0) || (shift == 16) || (shift == 32) || (shift == 48));
ASSERT((n != NULL) && (imm_s != NULL) && (imm_r != NULL));
ASSERT((width == kWRegSizeInBits) || (width == kXRegSizeInBits));
- bool negate = false;
-
// Logical immediates are encoded using parameters n, imm_s and imm_r using
// the following table:
//
- // N imms immr size S R
- // 1 ssssss rrrrrr 64 UInt(ssssss) UInt(rrrrrr)
- // 0 0sssss xrrrrr 32 UInt(sssss) UInt(rrrrr)
- // 0 10ssss xxrrrr 16 UInt(ssss) UInt(rrrr)
- // 0 110sss xxxrrr 8 UInt(sss) UInt(rrr)
- // 0 1110ss xxxxrr 4 UInt(ss) UInt(rr)
- // 0 11110s xxxxxr 2 UInt(s) UInt(r)
+ // N imms immr size S R
+ // 1 ssssss rrrrrr 64 UInt(ssssss) UInt(rrrrrr)
+ // 0 0sssss xrrrrr 32 UInt(sssss) UInt(rrrrr)
+ // 0 10ssss xxrrrr 16 UInt(ssss) UInt(rrrr)
+ // 0 110sss xxxrrr 8 UInt(sss) UInt(rrr)
+ // 0 1110ss xxxxrr 4 UInt(ss) UInt(rr)
+ // 0 11110s xxxxxr 2 UInt(s) UInt(r)
// (s bits must not be all set)
//
- // A pattern is constructed of size bits, where the least significant S+1 bits
- // are set. The pattern is rotated right by R, and repeated across a 32 or
- // 64-bit value, depending on destination register width.
+ // A pattern is constructed of size bits, where the least significant S+1
+ // bits are set. The pattern is rotated right by R, and repeated across a
+ // 32 or 64-bit value, depending on destination register width.
//
- // Put another way: the basic format of a logical immediate is a single
- // contiguous stretch of 1 bits, repeated across the whole word at intervals
- // given by a power of 2. To identify them quickly, we first locate the
- // lowest stretch of 1 bits, then the next 1 bit above that; that combination
- // is different for every logical immediate, so it gives us all the
- // information we need to identify the only logical immediate that our input
- // could be, and then we simply check if that's the value we actually have.
+ // To test if an arbitary immediate can be encoded using this scheme, an
+ // iterative algorithm is used.
//
- // (The rotation parameter does give the possibility of the stretch of 1 bits
- // going 'round the end' of the word. To deal with that, we observe that in
- // any situation where that happens the bitwise NOT of the value is also a
- // valid logical immediate. So we simply invert the input whenever its low bit
- // is set, and then we know that the rotated case can't arise.)
+ // TODO(mcapewel) This code does not consider using X/W register overlap to
+ // support 64-bit immediates where the top 32-bits are zero, and the bottom
+ // 32-bits are an encodable logical immediate.
- if (value & 1) {
- // If the low bit is 1, negate the value, and set a flag to remember that we
- // did (so that we can adjust the return values appropriately).
- negate = true;
- value = ~value;
+ // 1. If the value has all set or all clear bits, it can't be encoded.
+ if ((value == 0) || (value == 0xffffffffffffffffUL) ||
+ ((width == kWRegSizeInBits) && (value == 0xffffffff))) {
+ return false;
}
- if (width == kWRegSizeInBits) {
- // To handle 32-bit logical immediates, the very easiest thing is to repeat
- // the input value twice to make a 64-bit word. The correct encoding of that
- // as a logical immediate will also be the correct encoding of the 32-bit
- // value.
-
- // The most-significant 32 bits may not be zero (ie. negate is true) so
- // shift the value left before duplicating it.
- value <<= kWRegSizeInBits;
- value |= value >> kWRegSizeInBits;
- }
+ unsigned lead_zero = CountLeadingZeros(value, width);
+ unsigned lead_one = CountLeadingZeros(~value, width);
+ unsigned trail_zero = CountTrailingZeros(value, width);
+ unsigned trail_one = CountTrailingZeros(~value, width);
+ unsigned set_bits = CountSetBits(value, width);
+
+ // The fixed bits in the immediate s field.
+ // If width == 64 (X reg), start at 0xFFFFFF80.
+ // If width == 32 (W reg), start at 0xFFFFFFC0, as the iteration for 64-bit
+ // widths won't be executed.
+ int imm_s_fixed = (width == kXRegSizeInBits) ? -128 : -64;
+ int imm_s_mask = 0x3F;
+
+ for (;;) {
+ // 2. If the value is two bits wide, it can be encoded.
+ if (width == 2) {
+ *n = 0;
+ *imm_s = 0x3C;
+ *imm_r = (value & 3) - 1;
+ return true;
+ }
- // The basic analysis idea: imagine our input word looks like this.
- //
- // 0011111000111110001111100011111000111110001111100011111000111110
- // c b a
- // |<--d-->|
- //
- // We find the lowest set bit (as an actual power-of-2 value, not its index)
- // and call it a. Then we add a to our original number, which wipes out the
- // bottommost stretch of set bits and replaces it with a 1 carried into the
- // next zero bit. Then we look for the new lowest set bit, which is in
- // position b, and subtract it, so now our number is just like the original
- // but with the lowest stretch of set bits completely gone. Now we find the
- // lowest set bit again, which is position c in the diagram above. Then we'll
- // measure the distance d between bit positions a and c (using CLZ), and that
- // tells us that the only valid logical immediate that could possibly be equal
- // to this number is the one in which a stretch of bits running from a to just
- // below b is replicated every d bits.
- uint64_t a = LargestPowerOf2Divisor(value);
- uint64_t value_plus_a = value + a;
- uint64_t b = LargestPowerOf2Divisor(value_plus_a);
- uint64_t value_plus_a_minus_b = value_plus_a - b;
- uint64_t c = LargestPowerOf2Divisor(value_plus_a_minus_b);
-
- int d, clz_a, out_n;
- uint64_t mask;
-
- if (c != 0) {
- // The general case, in which there is more than one stretch of set bits.
- // Compute the repeat distance d, and set up a bitmask covering the basic
- // unit of repetition (i.e. a word with the bottom d bits set). Also, in all
- // of these cases the N bit of the output will be zero.
- clz_a = CountLeadingZeros(a, kXRegSizeInBits);
- int clz_c = CountLeadingZeros(c, kXRegSizeInBits);
- d = clz_a - clz_c;
- mask = ((UINT64_C(1) << d) - 1);
- out_n = 0;
- } else {
- // Handle degenerate cases.
- //
- // If any of those 'find lowest set bit' operations didn't find a set bit at
- // all, then the word will have been zero thereafter, so in particular the
- // last lowest_set_bit operation will have returned zero. So we can test for
- // all the special case conditions in one go by seeing if c is zero.
- if (a == 0) {
- // The input was zero (or all 1 bits, which will come to here too after we
- // inverted it at the start of the function), for which we just return
- // false.
- return false;
+ *n = (width == 64) ? 1 : 0;
+ *imm_s = ((imm_s_fixed | (set_bits - 1)) & imm_s_mask);
+ if ((lead_zero + set_bits) == width) {
+ *imm_r = 0;
} else {
- // Otherwise, if c was zero but a was not, then there's just one stretch
- // of set bits in our word, meaning that we have the trivial case of
- // d == 64 and only one 'repetition'. Set up all the same variables as in
- // the general case above, and set the N bit in the output.
- clz_a = CountLeadingZeros(a, kXRegSizeInBits);
- d = 64;
- mask = ~UINT64_C(0);
- out_n = 1;
+ *imm_r = (lead_zero > 0) ? (width - trail_zero) : lead_one;
}
- }
- // If the repeat period d is not a power of two, it can't be encoded.
- if (!IS_POWER_OF_TWO(d)) {
- return false;
- }
+ // 3. If the sum of leading zeros, trailing zeros and set bits is equal to
+ // the bit width of the value, it can be encoded.
+ if (lead_zero + trail_zero + set_bits == width) {
+ return true;
+ }
- if (((b - a) & ~mask) != 0) {
- // If the bit stretch (b - a) does not fit within the mask derived from the
- // repeat period, then fail.
- return false;
- }
+ // 4. If the sum of leading ones, trailing ones and unset bits in the
+ // value is equal to the bit width of the value, it can be encoded.
+ if (lead_one + trail_one + (width - set_bits) == width) {
+ return true;
+ }
- // The only possible option is b - a repeated every d bits. Now we're going to
- // actually construct the valid logical immediate derived from that
- // specification, and see if it equals our original input.
- //
- // To repeat a value every d bits, we multiply it by a number of the form
- // (1 + 2^d + 2^(2d) + ...), i.e. 0x0001000100010001 or similar. These can
- // be derived using a table lookup on CLZ(d).
- static const uint64_t multipliers[] = {
- 0x0000000000000001UL,
- 0x0000000100000001UL,
- 0x0001000100010001UL,
- 0x0101010101010101UL,
- 0x1111111111111111UL,
- 0x5555555555555555UL,
- };
- int multiplier_idx = CountLeadingZeros(d, kXRegSizeInBits) - 57;
- // Ensure that the index to the multipliers array is within bounds.
- ASSERT((multiplier_idx >= 0) &&
- (static_cast<size_t>(multiplier_idx) <
- (sizeof(multipliers) / sizeof(multipliers[0]))));
- uint64_t multiplier = multipliers[multiplier_idx];
- uint64_t candidate = (b - a) * multiplier;
-
- if (value != candidate) {
- // The candidate pattern doesn't match our input value, so fail.
- return false;
- }
+ // 5. If the most-significant half of the bitwise value is equal to the
+ // least-significant half, return to step 2 using the least-significant
+ // half of the value.
+ uint64_t mask = (1UL << (width >> 1)) - 1;
+ if ((value & mask) == ((value >> (width >> 1)) & mask)) {
+ width >>= 1;
+ set_bits >>= 1;
+ imm_s_fixed >>= 1;
+ continue;
+ }
- // We have a match! This is a valid logical immediate, so now we have to
- // construct the bits and pieces of the instruction encoding that generates
- // it.
-
- // Count the set bits in our basic stretch. The special case of clz(0) == -1
- // makes the answer come out right for stretches that reach the very top of
- // the word (e.g. numbers like 0xffffc00000000000).
- int clz_b = (b == 0) ? -1 : CountLeadingZeros(b, kXRegSizeInBits);
- int s = clz_a - clz_b;
-
- // Decide how many bits to rotate right by, to put the low bit of that basic
- // stretch in position a.
- int r;
- if (negate) {
- // If we inverted the input right at the start of this function, here's
- // where we compensate: the number of set bits becomes the number of clear
- // bits, and the rotation count is based on position b rather than position
- // a (since b is the location of the 'lowest' 1 bit after inversion).
- s = d - s;
- r = (clz_b + 1) & (d - 1);
- } else {
- r = (clz_a + 1) & (d - 1);
+ // 6. Otherwise, the value can't be encoded.
+ return false;
}
-
- // Now we're done, except for having to encode the S output in such a way that
- // it gives both the number of set bits and the length of the repeated
- // segment. The s field is encoded like this:
- //
- // imms size S
- // ssssss 64 UInt(ssssss)
- // 0sssss 32 UInt(sssss)
- // 10ssss 16 UInt(ssss)
- // 110sss 8 UInt(sss)
- // 1110ss 4 UInt(ss)
- // 11110s 2 UInt(s)
- //
- // So we 'or' (-d << 1) with our computed s to form imms.
- *n = out_n;
- *imm_s = ((-d << 1) | (s - 1)) & 0x3f;
- *imm_r = r;
-
- return true;
}
__ Mov(w4, 0x00001234L);
__ Mov(w5, 0x12340000L);
__ Mov(w6, 0x12345678L);
- __ Mov(w7, (int32_t)0x80000000);
- __ Mov(w8, (int32_t)0xffff0000);
- __ Mov(w9, kWMinInt);
END();
RUN();
ASSERT_EQUAL_64(0x00001234L, x4);
ASSERT_EQUAL_64(0x12340000L, x5);
ASSERT_EQUAL_64(0x12345678L, x6);
- ASSERT_EQUAL_64(0x80000000L, x7);
- ASSERT_EQUAL_64(0xffff0000L, x8);
- ASSERT_EQUAL_32(kWMinInt, w9);
TEARDOWN();
}
__ Orr(x10, x0, Operand(0x1234567890abcdefUL));
__ Orr(w11, w1, Operand(0x90abcdef));
-
- __ Orr(w12, w0, kWMinInt);
- __ Eor(w13, w0, kWMinInt);
END();
RUN();
ASSERT_EQUAL_64(0xf0f0f0f0f0f0f0f0UL, x1);
ASSERT_EQUAL_64(0x1234567890abcdefUL, x10);
ASSERT_EQUAL_64(0xf0fbfdffUL, x11);
- ASSERT_EQUAL_32(kWMinInt, w12);
- ASSERT_EQUAL_32(kWMinInt, w13);
TEARDOWN();
}
__ Add(w12, w0, Operand(0x12345678));
__ Add(w13, w1, Operand(0xffffffff));
- __ Add(w18, w0, Operand(kWMinInt));
- __ Sub(w19, w0, Operand(kWMinInt));
-
__ Sub(x20, x0, Operand(0x1234567890abcdefUL));
+
__ Sub(w21, w0, Operand(0x12345678));
END();
ASSERT_EQUAL_32(0x12345678, w12);
ASSERT_EQUAL_64(0x0, x13);
- ASSERT_EQUAL_32(kWMinInt, w18);
- ASSERT_EQUAL_32(kWMinInt, w19);
-
ASSERT_EQUAL_64(-0x1234567890abcdefUL, x20);
+
ASSERT_EQUAL_32(-0x12345678, w21);
TEARDOWN();
projects / platform / upstream / v8.git / commitdiff