Merge pull request #9869 from JosJuice/jitarm64-constexpr-isimmlogical

JitArm64: Encode logical immediates at compile-time where possible

3 files changed, 292 insertions, 244 deletions

diff --git a/Source/Core/Common/Arm64Emitter.cpp b/Source/Core/Common/Arm64Emitter.cpp
index 141336e212..2e7cd2fd4d 100644
--- a/Source/Core/Common/Arm64Emitter.cpp
+++ b/Source/Core/Common/Arm64Emitter.cpp
@@ -28,11 +28,6 @@ namespace Arm64Gen
 {
 namespace
 {
-uint64_t LargestPowerOf2Divisor(uint64_t value)
-{
-  return value & -(int64_t)value;
-}
-
 // For ADD/SUB
 std::optional<std::pair<u32, bool>> IsImmArithmetic(uint64_t input)
 {
@@ -45,214 +40,6 @@ std::optional<std::pair<u32, bool>> IsImmArithmetic(uint64_t input)
   return std::nullopt;
 }
 
-// For AND/TST/ORR/EOR etc
-std::optional<std::tuple<u32, u32, u32>> IsImmLogical(u64 value, u32 width)
-{
-  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)
-  // (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.
-  //
-  // 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.
-  //
-  // (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.)
-
-  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;
-  }
-
-  constexpr int kWRegSizeInBits = 32;
-
-  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;
-  }
-
-  // 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 = Common::CountLeadingZeros(a);
-    int clz_c = Common::CountLeadingZeros(c);
-    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 std::nullopt;
-    }
-    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 = Common::CountLeadingZeros(a);
-      d = 64;
-      mask = ~UINT64_C(0);
-      out_n = 1;
-    }
-  }
-
-  // If the repeat period d is not a power of two, it can't be encoded.
-  if (!MathUtil::IsPow2<u64>(d))
-    return std::nullopt;
-
-  // If the bit stretch (b - a) does not fit within the mask derived from the
-  // repeat period, then fail.
-  if (((b - a) & ~mask) != 0)
-    return std::nullopt;
-
-  // 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 std::array<uint64_t, 6> multipliers = {{
-      0x0000000000000001UL,
-      0x0000000100000001UL,
-      0x0001000100010001UL,
-      0x0101010101010101UL,
-      0x1111111111111111UL,
-      0x5555555555555555UL,
-  }};
-
-  const int multiplier_idx = Common::CountLeadingZeros((u64)d) - 57;
-
-  // Ensure that the index to the multipliers array is within bounds.
-  DEBUG_ASSERT((multiplier_idx >= 0) && (static_cast<size_t>(multiplier_idx) < multipliers.size()));
-
-  const u64 multiplier = multipliers[multiplier_idx];
-  const u64 candidate = (b - a) * multiplier;
-
-  // The candidate pattern doesn't match our input value, so fail.
-  if (value != candidate)
-    return std::nullopt;
-
-  // 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).
-  const int clz_b = (b == 0) ? -1 : Common::CountLeadingZeros(b);
-  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);
-  }
-
-  // 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.
-  return std::tuple{
-      static_cast<u32>(out_n),
-      static_cast<u32>(((-d << 1) | (s - 1)) & 0x3f),
-      static_cast<u32>(r),
-  };
-}
-
 float FPImm8ToFloat(u8 bits)
 {
   const u32 sign = bits >> 7;
@@ -780,10 +567,18 @@ void ARM64XEmitter::EncodeLogicalImmInst(u32 op, ARM64Reg Rd, ARM64Reg Rn, u32 i
   // Use Rn to determine bitness here.
   bool b64Bit = Is64Bit(Rn);
 
+  ASSERT_MSG(DYNAREC, b64Bit || !n, "64-bit logical immediate does not fit in 32-bit register");
+
   Write32((b64Bit << 31) | (op << 29) | (0x24 << 23) | (n << 22) | (immr << 16) | (imms << 10) |
           (DecodeReg(Rn) << 5) | DecodeReg(Rd));
 }
 
+void ARM64XEmitter::EncodeLogicalImmInst(u32 op, ARM64Reg Rd, ARM64Reg Rn, LogicalImm imm)
+{
+  ASSERT_MSG(DYNAREC, imm.valid, "Invalid logical immediate");
+  EncodeLogicalImmInst(op, Rd, Rn, imm.r, imm.s, imm.n);
+}
+
 void ARM64XEmitter::EncodeLoadStorePair(u32 op, u32 load, IndexType type, ARM64Reg Rt, ARM64Reg Rt2,
                                         ARM64Reg Rn, s32 imm)
 {
@@ -1545,22 +1340,42 @@ void ARM64XEmitter::AND(ARM64Reg Rd, ARM64Reg Rn, u32 immr, u32 imms, bool inver
 {
   EncodeLogicalImmInst(0, Rd, Rn, immr, imms, invert);
 }
+void ARM64XEmitter::AND(ARM64Reg Rd, ARM64Reg Rn, LogicalImm imm)
+{
+  EncodeLogicalImmInst(0, Rd, Rn, imm);
+}
 void ARM64XEmitter::ANDS(ARM64Reg Rd, ARM64Reg Rn, u32 immr, u32 imms, bool invert)
 {
   EncodeLogicalImmInst(3, Rd, Rn, immr, imms, invert);
 }
+void ARM64XEmitter::ANDS(ARM64Reg Rd, ARM64Reg Rn, LogicalImm imm)
+{
+  EncodeLogicalImmInst(3, Rd, Rn, imm);
+}
 void ARM64XEmitter::EOR(ARM64Reg Rd, ARM64Reg Rn, u32 immr, u32 imms, bool invert)
 {
   EncodeLogicalImmInst(2, Rd, Rn, immr, imms, invert);
 }
+void ARM64XEmitter::EOR(ARM64Reg Rd, ARM64Reg Rn, LogicalImm imm)
+{
+  EncodeLogicalImmInst(2, Rd, Rn, imm);
+}
 void ARM64XEmitter::ORR(ARM64Reg Rd, ARM64Reg Rn, u32 immr, u32 imms, bool invert)
 {
   EncodeLogicalImmInst(1, Rd, Rn, immr, imms, invert);
 }
+void ARM64XEmitter::ORR(ARM64Reg Rd, ARM64Reg Rn, LogicalImm imm)
+{
+  EncodeLogicalImmInst(1, Rd, Rn, imm);
+}
 void ARM64XEmitter::TST(ARM64Reg Rn, u32 immr, u32 imms, bool invert)
 {
   EncodeLogicalImmInst(3, Is64Bit(Rn) ? ARM64Reg::ZR : ARM64Reg::WZR, Rn, immr, imms, invert);
 }
+void ARM64XEmitter::TST(ARM64Reg Rn, LogicalImm imm)
+{
+  EncodeLogicalImmInst(3, Is64Bit(Rn) ? ARM64Reg::ZR : ARM64Reg::WZR, Rn, imm);
+}
 
 // Add/subtract (immediate)
 void ARM64XEmitter::ADD(ARM64Reg Rd, ARM64Reg Rn, u32 imm, bool shift)
@@ -2067,13 +1882,13 @@ void ARM64XEmitter::MOVI2RImpl(ARM64Reg Rd, T imm)
                           (imm & 0xFFFF'FFFF'0000'0000) | (imm >> 32),
                           (imm << 48) | (imm & 0x0000'FFFF'FFFF'0000) | (imm >> 48)})
       {
-        if (IsImmLogical(orr_imm, 64))
+        if (LogicalImm(orr_imm, 64))
           try_base(orr_imm, Approach::ORRBase, false);
       }
     }
     else
     {
-      if (IsImmLogical(imm, 32))
+      if (LogicalImm(imm, 32))
         try_base(imm, Approach::ORRBase, false);
     }
   }
@@ -4127,10 +3942,9 @@ void ARM64XEmitter::ANDI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch)
   if (!Is64Bit(Rn))
     imm &= 0xFFFFFFFF;
 
-  if (const auto result = IsImmLogical(imm, Is64Bit(Rn) ? 64 : 32))
+  if (const auto result = LogicalImm(imm, Is64Bit(Rn) ? 64 : 32))
   {
-    const auto& [n, imm_s, imm_r] = *result;
-    AND(Rd, Rn, imm_r, imm_s, n != 0);
+    AND(Rd, Rn, result);
   }
   else
   {
@@ -4144,10 +3958,9 @@ void ARM64XEmitter::ANDI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch)
 
 void ARM64XEmitter::ORRI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch)
 {
-  if (const auto result = IsImmLogical(imm, Is64Bit(Rn) ? 64 : 32))
+  if (const auto result = LogicalImm(imm, Is64Bit(Rn) ? 64 : 32))
   {
-    const auto& [n, imm_s, imm_r] = *result;
-    ORR(Rd, Rn, imm_r, imm_s, n != 0);
+    ORR(Rd, Rn, result);
   }
   else
   {
@@ -4161,10 +3974,9 @@ void ARM64XEmitter::ORRI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch)
 
 void ARM64XEmitter::EORI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch)
 {
-  if (const auto result = IsImmLogical(imm, Is64Bit(Rn) ? 64 : 32))
+  if (const auto result = LogicalImm(imm, Is64Bit(Rn) ? 64 : 32))
   {
-    const auto& [n, imm_s, imm_r] = *result;
-    EOR(Rd, Rn, imm_r, imm_s, n != 0);
+    EOR(Rd, Rn, result);
   }
   else
   {
@@ -4178,10 +3990,9 @@ void ARM64XEmitter::EORI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch)
 
 void ARM64XEmitter::ANDSI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch)
 {
-  if (const auto result = IsImmLogical(imm, Is64Bit(Rn) ? 64 : 32))
+  if (const auto result = LogicalImm(imm, Is64Bit(Rn) ? 64 : 32))
   {
-    const auto& [n, imm_s, imm_r] = *result;
-    ANDS(Rd, Rn, imm_r, imm_s, n != 0);
+    ANDS(Rd, Rn, result);
   }
   else
   {
@@ -4342,10 +4153,9 @@ bool ARM64XEmitter::TryCMPI2R(ARM64Reg Rn, u64 imm)
 
 bool ARM64XEmitter::TryANDI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm)
 {
-  if (const auto result = IsImmLogical(imm, Is64Bit(Rd) ? 64 : 32))
+  if (const auto result = LogicalImm(imm, Is64Bit(Rd) ? 64 : 32))
   {
-    const auto& [n, imm_s, imm_r] = *result;
-    AND(Rd, Rn, imm_r, imm_s, n != 0);
+    AND(Rd, Rn, result);
     return true;
   }
 
@@ -4354,10 +4164,9 @@ bool ARM64XEmitter::TryANDI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm)
 
 bool ARM64XEmitter::TryORRI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm)
 {
-  if (const auto result = IsImmLogical(imm, Is64Bit(Rd) ? 64 : 32))
+  if (const auto result = LogicalImm(imm, Is64Bit(Rd) ? 64 : 32))
   {
-    const auto& [n, imm_s, imm_r] = *result;
-    ORR(Rd, Rn, imm_r, imm_s, n != 0);
+    ORR(Rd, Rn, result);
     return true;
   }
 
@@ -4366,10 +4175,9 @@ bool ARM64XEmitter::TryORRI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm)
 
 bool ARM64XEmitter::TryEORI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm)
 {
-  if (const auto result = IsImmLogical(imm, Is64Bit(Rd) ? 64 : 32))
+  if (const auto result = LogicalImm(imm, Is64Bit(Rd) ? 64 : 32))
   {
-    const auto& [n, imm_s, imm_r] = *result;
-    EOR(Rd, Rn, imm_r, imm_s, n != 0);
+    EOR(Rd, Rn, result);
     return true;
   }
 
diff --git a/Source/Core/Common/Arm64Emitter.h b/Source/Core/Common/Arm64Emitter.h
index 5702bebbd9..3f5c18d8c9 100644
--- a/Source/Core/Common/Arm64Emitter.h
+++ b/Source/Core/Common/Arm64Emitter.h
@@ -5,12 +5,17 @@
 
 #include <cstring>
 #include <functional>
+#include <optional>
+#include <utility>
 
 #include "Common/ArmCommon.h"
 #include "Common/Assert.h"
 #include "Common/BitSet.h"
+#include "Common/BitUtils.h"
 #include "Common/CodeBlock.h"
 #include "Common/Common.h"
+#include "Common/CommonTypes.h"
+#include "Common/MathUtil.h"
 
 namespace Arm64Gen
 {
@@ -496,6 +501,225 @@ public:
   bool IsExtended() const { return m_type == TypeSpecifier::ExtendedReg; }
 };
 
+struct LogicalImm
+{
+  constexpr LogicalImm() {}
+
+  constexpr LogicalImm(u8 r_, u8 s_, bool n_) : r(r_), s(s_), n(n_), valid(true) {}
+
+  constexpr LogicalImm(u64 value, u32 width)
+  {
+    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)
+    // (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.
+    //
+    // 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.
+    //
+    // (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.)
+
+    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;
+    }
+
+    constexpr int kWRegSizeInBits = 32;
+
+    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;
+    }
+
+    // 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.
+    u64 a = Common::LargestPowerOf2Divisor(value);
+    u64 value_plus_a = value + a;
+    u64 b = Common::LargestPowerOf2Divisor(value_plus_a);
+    u64 value_plus_a_minus_b = value_plus_a - b;
+    u64 c = Common::LargestPowerOf2Divisor(value_plus_a_minus_b);
+
+    int d = 0, clz_a = 0, out_n = 0;
+    u64 mask = 0;
+
+    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 = Common::CountLeadingZeros(a);
+      int clz_c = Common::CountLeadingZeros(c);
+      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), which is invalid.
+        return;
+      }
+      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 = Common::CountLeadingZeros(a);
+        d = 64;
+        mask = ~UINT64_C(0);
+        out_n = 1;
+      }
+    }
+
+    // If the repeat period d is not a power of two, it can't be encoded.
+    if (!MathUtil::IsPow2<u64>(d))
+      return;
+
+    // If the bit stretch (b - a) does not fit within the mask derived from the
+    // repeat period, then fail.
+    if (((b - a) & ~mask) != 0)
+      return;
+
+    // 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).
+    constexpr std::array<u64, 6> multipliers = {{
+        0x0000000000000001UL,
+        0x0000000100000001UL,
+        0x0001000100010001UL,
+        0x0101010101010101UL,
+        0x1111111111111111UL,
+        0x5555555555555555UL,
+    }};
+
+    const int multiplier_idx = Common::CountLeadingZeros((u64)d) - 57;
+
+    // Ensure that the index to the multipliers array is within bounds.
+    DEBUG_ASSERT((multiplier_idx >= 0) &&
+                 (static_cast<size_t>(multiplier_idx) < multipliers.size()));
+
+    const u64 multiplier = multipliers[multiplier_idx];
+    const u64 candidate = (b - a) * multiplier;
+
+    // The candidate pattern doesn't match our input value, so fail.
+    if (value != candidate)
+      return;
+
+    // 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.
+    n = out_n;
+
+    // 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).
+    const int clz_b = (b == 0) ? -1 : Common::CountLeadingZeros(b);
+    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.
+    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);
+    }
+
+    // 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.
+    s = ((-d << 1) | (s - 1)) & 0x3f;
+
+    valid = true;
+  }
+
+  constexpr operator bool() const { return valid; }
+
+  u8 r = 0;
+  u8 s = 0;
+  bool n = false;
+  bool valid = false;
+};
+
 class ARM64XEmitter
 {
   friend class ARM64FloatEmitter;
@@ -531,6 +755,7 @@ private:
   void EncodeLoadStoreRegisterOffset(u32 size, u32 opc, ARM64Reg Rt, ARM64Reg Rn, ArithOption Rm);
   void EncodeAddSubImmInst(u32 op, bool flags, u32 shift, u32 imm, ARM64Reg Rn, ARM64Reg Rd);
   void EncodeLogicalImmInst(u32 op, ARM64Reg Rd, ARM64Reg Rn, u32 immr, u32 imms, int n);
+  void EncodeLogicalImmInst(u32 op, ARM64Reg Rd, ARM64Reg Rn, LogicalImm imm);
   void EncodeLoadStorePair(u32 op, u32 load, IndexType type, ARM64Reg Rt, ARM64Reg Rt2, ARM64Reg Rn,
                            s32 imm);
   void EncodeAddressInst(u32 op, ARM64Reg Rd, s32 imm);
@@ -772,10 +997,15 @@ public:
 
   // Logical (immediate)
   void AND(ARM64Reg Rd, ARM64Reg Rn, u32 immr, u32 imms, bool invert = false);
+  void AND(ARM64Reg Rd, ARM64Reg Rn, LogicalImm imm);
   void ANDS(ARM64Reg Rd, ARM64Reg Rn, u32 immr, u32 imms, bool invert = false);
+  void ANDS(ARM64Reg Rd, ARM64Reg Rn, LogicalImm imm);
   void EOR(ARM64Reg Rd, ARM64Reg Rn, u32 immr, u32 imms, bool invert = false);
+  void EOR(ARM64Reg Rd, ARM64Reg Rn, LogicalImm imm);
   void ORR(ARM64Reg Rd, ARM64Reg Rn, u32 immr, u32 imms, bool invert = false);
+  void ORR(ARM64Reg Rd, ARM64Reg Rn, LogicalImm imm);
   void TST(ARM64Reg Rn, u32 immr, u32 imms, bool invert = false);
+  void TST(ARM64Reg Rn, LogicalImm imm);
   // Add/subtract (immediate)
   void ADD(ARM64Reg Rd, ARM64Reg Rn, u32 imm, bool shift = false);
   void ADDS(ARM64Reg Rd, ARM64Reg Rn, u32 imm, bool shift = false);
@@ -893,17 +1123,17 @@ public:
     MOVI2R(Rd, (uintptr_t)ptr);
   }
 
-  // Wrapper around AND x, y, imm etc. If you are sure the imm will work, no need to pass a scratch
-  // register.
-  void ANDI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch = ARM64Reg::INVALID_REG);
-  void ANDSI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch = ARM64Reg::INVALID_REG);
-  void TSTI2R(ARM64Reg Rn, u64 imm, ARM64Reg scratch = ARM64Reg::INVALID_REG)
+  // Wrapper around AND x, y, imm etc.
+  // If you are sure the imm will work, preferably construct a LogicalImm directly instead,
+  // since that is constexpr and thus can be done at compile-time for constant values.
+  void ANDI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch);
+  void ANDSI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch);
+  void TSTI2R(ARM64Reg Rn, u64 imm, ARM64Reg scratch)
   {
     ANDSI2R(Is64Bit(Rn) ? ARM64Reg::ZR : ARM64Reg::WZR, Rn, imm, scratch);
   }
-  void ORRI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch = ARM64Reg::INVALID_REG);
-  void EORI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch = ARM64Reg::INVALID_REG);
-  void CMPI2R(ARM64Reg Rn, u64 imm, ARM64Reg scratch = ARM64Reg::INVALID_REG);
+  void ORRI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch);
+  void EORI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch);
 
   void ADDI2R_internal(ARM64Reg Rd, ARM64Reg Rn, u64 imm, bool negative, bool flags,
                        ARM64Reg scratch);
@@ -911,6 +1141,7 @@ public:
   void ADDSI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch = ARM64Reg::INVALID_REG);
   void SUBI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch = ARM64Reg::INVALID_REG);
   void SUBSI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm, ARM64Reg scratch = ARM64Reg::INVALID_REG);
+  void CMPI2R(ARM64Reg Rn, u64 imm, ARM64Reg scratch = ARM64Reg::INVALID_REG);
 
   bool TryADDI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm);
   bool TrySUBI2R(ARM64Reg Rd, ARM64Reg Rn, u64 imm);
diff --git a/Source/Core/Common/BitUtils.h b/Source/Core/Common/BitUtils.h
index d4d23d63d8..09ab4bd78c 100644
--- a/Source/Core/Common/BitUtils.h
+++ b/Source/Core/Common/BitUtils.h
@@ -413,4 +413,13 @@ constexpr int CountLeadingZeros(uint32_t value)
 
 #undef CONSTEXPR_FROM_INTRINSIC
 
+template <typename T>
+constexpr T LargestPowerOf2Divisor(T value)
+{
+  static_assert(std::is_unsigned<T>(),
+                "LargestPowerOf2Divisor only makes sense for unsigned types.");
+
+  return value & -static_cast<std::make_signed_t<T>>(value);
+}
+
 }  // namespace Common