MIPS32: Simplify set of condition codes.

src/mips/constants-mips.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef  V8_MIPS_CONSTANTS_H_
 #define  V8_MIPS_CONSTANTS_H_
 #include "src/globals.h"
 // UNIMPLEMENTED_ macro for MIPS.
 #ifdef DEBUG
 #define UNIMPLEMENTED_MIPS()                                                  \
@@ skipping 590 matching lines @@
 
   // POP76 Encoding of rs Field.
   JIALC = ((0 << 5) + 0),
 
   NULLSF = 0
 };
 
 
 // ----- Emulated conditions.
 // On MIPS we use this enum to abstract from conditional branch instructions.
-// The 'U' prefix is used to specify unsigned comparisons.
 // Opposite conditions must be paired as odd/even numbers
 // because 'NegateCondition' function flips LSB to negate condition.
+// CC values for any comparison involving equality has LS bit set.
+// TODO(plind): remove unused conditions, and renumber.
 enum Condition {
   // Any value < 0 is considered no_condition.
   kNoCondition = -1,
-  overflow = 0,
-  no_overflow = 1,
-  Uless = 2,
-  Ugreater_equal = 3,
-  Uless_equal = 4,
-  Ugreater = 5,
-  equal = 6,
-  not_equal = 7,  // Unordered or Not Equal.
-  negative = 8,
-  positive = 9,
-  parity_even = 10,
-  parity_odd = 11,
-  less = 12,
-  greater_equal = 13,
-  less_equal = 14,
-  greater = 15,
+  // overflow = 0,
+  // no_overflow = 1,
+
+  lo = 2,  // Unsigned less than (lower)
+  hs = 3,  // Unsigned greater than or equal (higher or same).
+  hi = 4,  // Unsigned greater than (higher).
+  ls = 5,  // Unsigned less than or equal (lower or same).
+  ne = 6,  // Unordered or Not Equal.
+  eq = 7,  // Equal.
+  // mi = 8,
+  // pl = 9,
+  // parity_even = 10,
+  // parity_odd = 11,
+  lt = 12,   // Less than.
+  ge = 13,   // Great than or equal.
+  gt = 14,   // Greater than.
+  le = 15,   // Less than or equal.
   ueq = 16,  // Unordered or Equal.
   ogl = 17,  // Ordered and Not Equal.
   cc_always = 18,
 
   // Aliases.
-  carry = Uless,
-  not_carry = Ugreater_equal,
-  zero = equal,
-  eq = equal,
-  not_zero = not_equal,
-  ne = not_equal,
-  nz = not_equal,
-  sign = negative,
-  not_sign = positive,
-  mi = negative,
-  pl = positive,
-  hi = Ugreater,
-  ls = Uless_equal,
-  ge = greater_equal,
-  lt = less,
-  gt = greater,
-  le = less_equal,
-  hs = Ugreater_equal,
-  lo = Uless,
   al = cc_always,
-  ult = Uless,
-  uge = Ugreater_equal,
-  ule = Uless_equal,
-  ugt = Ugreater,
+  nz = ne,  // TODO(plind): consider deleting nz
+
+  // // TODO(plind): Currently unused aliases - delete.
+  // carry = Uless,
+  // not_carry = Ugreater_equal,
+  // equal = eq,
+  // zero = equal,
+  // not_equal = ne,
+  // not_zero = not_equal,
+
+  // negative = mi,
+  // positive = pl,
+  // sign = negative,
+  // not_sign = positive,
+
+  // // TODO(plind): These aliases ARE used, and should likey be factored out.
+  Ugreater = hi,
+  Uless_equal = ls,
+  greater_equal = ge,
+  less = lt,
+  greater = gt,
+  less_equal = le,
+  Ugreater_equal = hs,
+  Uless = lo,
+
+  // TODO(plind): understand these aliases for FP, do we need them?
+  ult = lo,
+  uge = hs,
+  ule = ls,
+  ugt = hi,
+
   cc_default = kNoCondition
 };
 
 
+// Conditions are assigned so LSB is set for condition including equality.
+inline bool ConditionIncludesEquality(Condition cc) {
+  DCHECK(cc != cc_always);
+  // TODO(plind): consider DCHECK to validate LSB set properly.
+  return (cc & 1);
+}
+

[paul.l..., 2015/09/04 03:45:24]

This function is no longer needed. I had thought this would be useful in a TF
function, but I was wrong.

That also means that the re-numbering above is not important, nor is this
comment:
// CC values for any comparison involving equality has LS bit set.

though it does not hurt anything, as long as we also comply with this comment:
// Opposite conditions must be paired as odd/even numbers

This is not urgent now, but think this (when finished and bogus aliases are
removed from rest of mips port) would be a nice cimplication and consistency
cleanup. What do you guys think?

[balazs.kilvady, 2015/09/04 09:27:45]

I think the unsused function should be removed but we can keep the odd/even
number pairs for conditions codes as it does not hurt now and might be useful
later.

+
 // Returns the equivalent of !cc.
 // Negation of the default kNoCondition (-1) results in a non-default
 // no_condition value (-2). As long as tests for no_condition check
 // for condition < 0, this will work as expected.
 inline Condition NegateCondition(Condition cc) {
   DCHECK(cc != cc_always);
   return static_cast<Condition>(cc ^ 1);
 }
 
 
@@ skipping 26 matching lines @@
       return ueq;
     default:
       return cc;
   }
 }
 
 
 // Commute a condition such that {a cond b == b cond' a}.
 inline Condition CommuteCondition(Condition cc) {
   switch (cc) {
-    case Uless:
-      return Ugreater;
-    case Ugreater:
-      return Uless;
-    case Ugreater_equal:
-      return Uless_equal;
-    case Uless_equal:
-      return Ugreater_equal;
-    case less:
-      return greater;
-    case greater:
-      return less;
-    case greater_equal:
-      return less_equal;
-    case less_equal:
-      return greater_equal;
+    case lo:
+      return hi;
+    case hi:
+      return lo;
+    case hs:
+      return ls;
+    case ls:
+      return hs;
+    case lt:
+      return gt;
+    case gt:
+      return lt;
+    case ge:
+      return le;
+    case le:
+      return ge;
     default:
       return cc;
   }
 }
 
 
 // ----- Coprocessor conditions.
 enum FPUCondition {
   kNoFPUCondition = -1,
 
@@ skipping 302 matching lines @@
 // JS argument slots size.
 const int kJSArgsSlotsSize = 0 * Instruction::kInstrSize;
 // Assembly builtins argument slots size.
 const int kBArgsSlotsSize = 0 * Instruction::kInstrSize;
 
 const int kBranchReturnOffset = 2 * Instruction::kInstrSize;
 
 } }   // namespace v8::internal
 
 #endif    // #ifndef V8_MIPS_CONSTANTS_H_