# HG changeset patch
# User Adrian Wielgosik <adrian.wielgosik@gmail.com>
# Date 1480251985 -3600
#      Sun Nov 27 14:06:25 2016 +0100
# Node ID 524b21435023bf1b98699847408c3c528beb16a5
# Parent  876bee0bd0ba55d64687e233021425f85fb57e05
const removal

diff -r 876bee0bd0ba -r 524b21435023 Lib/test/test_dis.py
--- a/Lib/test/test_dis.py	Sat Nov 26 14:04:40 2016 -0800
+++ b/Lib/test/test_dis.py	Sun Nov 27 14:06:25 2016 +0100
@@ -679,9 +679,9 @@
 # End fodder for opinfo generation tests
 expected_outer_line = 1
 _line_offset = outer.__code__.co_firstlineno - 1
-code_object_f = outer.__code__.co_consts[3]
+code_object_f = outer.__code__.co_consts[1]
 expected_f_line = code_object_f.co_firstlineno - _line_offset
-code_object_inner = code_object_f.co_consts[3]
+code_object_inner = code_object_f.co_consts[1]
 expected_inner_line = code_object_inner.co_firstlineno - _line_offset
 expected_jumpy_line = 1
 
@@ -706,22 +706,22 @@
 
 Instruction = dis.Instruction
 expected_opinfo_outer = [
-  Instruction(opname='LOAD_CONST', opcode=100, arg=8, argval=(3, 4), argrepr='(3, 4)', offset=0, starts_line=2, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=6, argval=(3, 4), argrepr='(3, 4)', offset=0, starts_line=2, is_jump_target=False),
   Instruction(opname='LOAD_CLOSURE', opcode=135, arg=0, argval='a', argrepr='a', offset=2, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CLOSURE', opcode=135, arg=1, argval='b', argrepr='b', offset=4, starts_line=None, is_jump_target=False),
   Instruction(opname='BUILD_TUPLE', opcode=102, arg=2, argval=2, argrepr='', offset=6, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CONST', opcode=100, arg=3, argval=code_object_f, argrepr=repr(code_object_f), offset=8, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CONST', opcode=100, arg=4, argval='outer.<locals>.f', argrepr="'outer.<locals>.f'", offset=10, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=1, argval=code_object_f, argrepr=repr(code_object_f), offset=8, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=2, argval='outer.<locals>.f', argrepr="'outer.<locals>.f'", offset=10, starts_line=None, is_jump_target=False),
   Instruction(opname='MAKE_FUNCTION', opcode=132, arg=9, argval=9, argrepr='', offset=12, starts_line=None, is_jump_target=False),
   Instruction(opname='STORE_FAST', opcode=125, arg=2, argval='f', argrepr='f', offset=14, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_GLOBAL', opcode=116, arg=0, argval='print', argrepr='print', offset=16, starts_line=7, is_jump_target=False),
   Instruction(opname='LOAD_DEREF', opcode=136, arg=0, argval='a', argrepr='a', offset=18, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_DEREF', opcode=136, arg=1, argval='b', argrepr='b', offset=20, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CONST', opcode=100, arg=5, argval='', argrepr="''", offset=22, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CONST', opcode=100, arg=6, argval=1, argrepr='1', offset=24, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=3, argval='', argrepr="''", offset=22, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=4, argval=1, argrepr='1', offset=24, starts_line=None, is_jump_target=False),
   Instruction(opname='BUILD_LIST', opcode=103, arg=0, argval=0, argrepr='', offset=26, starts_line=None, is_jump_target=False),
   Instruction(opname='BUILD_MAP', opcode=105, arg=0, argval=0, argrepr='', offset=28, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CONST', opcode=100, arg=7, argval='Hello world!', argrepr="'Hello world!'", offset=30, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=5, argval='Hello world!', argrepr="'Hello world!'", offset=30, starts_line=None, is_jump_target=False),
   Instruction(opname='CALL_FUNCTION', opcode=131, arg=7, argval=7, argrepr='', offset=32, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=34, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_FAST', opcode=124, arg=2, argval='f', argrepr='f', offset=36, starts_line=8, is_jump_target=False),
@@ -729,14 +729,14 @@
 ]
 
 expected_opinfo_f = [
-  Instruction(opname='LOAD_CONST', opcode=100, arg=5, argval=(5, 6), argrepr='(5, 6)', offset=0, starts_line=3, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=3, argval=(5, 6), argrepr='(5, 6)', offset=0, starts_line=3, is_jump_target=False),
   Instruction(opname='LOAD_CLOSURE', opcode=135, arg=2, argval='a', argrepr='a', offset=2, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CLOSURE', opcode=135, arg=3, argval='b', argrepr='b', offset=4, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CLOSURE', opcode=135, arg=0, argval='c', argrepr='c', offset=6, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CLOSURE', opcode=135, arg=1, argval='d', argrepr='d', offset=8, starts_line=None, is_jump_target=False),
   Instruction(opname='BUILD_TUPLE', opcode=102, arg=4, argval=4, argrepr='', offset=10, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CONST', opcode=100, arg=3, argval=code_object_inner, argrepr=repr(code_object_inner), offset=12, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CONST', opcode=100, arg=4, argval='outer.<locals>.f.<locals>.inner', argrepr="'outer.<locals>.f.<locals>.inner'", offset=14, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=1, argval=code_object_inner, argrepr=repr(code_object_inner), offset=12, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=2, argval='outer.<locals>.f.<locals>.inner', argrepr="'outer.<locals>.f.<locals>.inner'", offset=14, starts_line=None, is_jump_target=False),
   Instruction(opname='MAKE_FUNCTION', opcode=132, arg=9, argval=9, argrepr='', offset=16, starts_line=None, is_jump_target=False),
   Instruction(opname='STORE_FAST', opcode=125, arg=2, argval='inner', argrepr='inner', offset=18, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_GLOBAL', opcode=116, arg=0, argval='print', argrepr='print', offset=20, starts_line=5, is_jump_target=False),
diff -r 876bee0bd0ba -r 524b21435023 Python/peephole.c
--- a/Python/peephole.c	Sat Nov 26 14:04:40 2016 -0800
+++ b/Python/peephole.c	Sun Nov 27 14:06:25 2016 +0100
@@ -22,37 +22,61 @@
 #define ISBASICBLOCK(blocks, start, end) \
     (blocks[start]==blocks[end])
 
+struct const_uses_entry {
+    unsigned int uses;
+    unsigned int relocation;
+};
 
 #define CONST_STACK_CREATE() { \
     const_stack_size = 256; \
-    const_stack = PyMem_New(PyObject *, const_stack_size); \
+    const_stack = PyMem_New(unsigned int, const_stack_size); \
     if (!const_stack) { \
         PyErr_NoMemory(); \
         goto exitError; \
     } \
+    const_uses_curr_size = const_uses_size = PyList_GET_SIZE(consts); \
+    const_uses = PyMem_New(struct const_uses_entry, const_uses_size); \
+    if (!const_uses) { \
+        PyErr_NoMemory(); \
+        goto exitError; \
+    } \
+    memset(const_uses, 0, const_uses_size * sizeof(struct const_uses_entry)); \
     }
 
 #define CONST_STACK_DELETE() do { \
     if (const_stack) \
         PyMem_Free(const_stack); \
+        PyMem_Free(const_uses); \
     } while(0)
 
 #define CONST_STACK_LEN() ((unsigned)(const_stack_top + 1))
 
 #define CONST_STACK_PUSH_OP(i) do { \
-    PyObject *_x; \
     assert(_Py_OPCODE(codestr[i]) == LOAD_CONST); \
     assert(PyList_GET_SIZE(consts) > (Py_ssize_t)get_arg(codestr, i)); \
-    _x = PyList_GET_ITEM(consts, get_arg(codestr, i)); \
     if (++const_stack_top >= const_stack_size) { \
         const_stack_size *= 2; \
-        PyMem_Resize(const_stack, PyObject *, const_stack_size); \
+        PyMem_Resize(const_stack, unsigned int, const_stack_size); \
         if (!const_stack) { \
             PyErr_NoMemory(); \
             goto exitError; \
         } \
     } \
-    const_stack[const_stack_top] = _x; \
+    int arg = get_arg(codestr, i); \
+    const_stack[const_stack_top] = arg; \
+    if (arg >= const_uses_curr_size) {\
+        const_uses_curr_size = arg + 1; \
+        if (const_uses_curr_size > const_uses_size) {\
+            const_uses_size *= 2; \
+            PyMem_Resize(const_uses, struct const_uses_entry, const_uses_size); \
+            if (!const_uses) { \
+                PyErr_NoMemory(); \
+                goto exitError; \
+            } \
+            for (int z = arg; z < const_uses_size; ++z) const_uses[z].uses = 0; \
+        } \
+    }\
+    const_uses[arg].uses += 1; \
     in_consts = 1; \
     } while(0)
 
@@ -66,8 +90,12 @@
 #define CONST_STACK_POP(i) do { \
     assert(CONST_STACK_LEN() >= i); \
     const_stack_top -= i; \
+    for (unsigned int z = 0; z < i; ++z) \
+        const_uses[const_stack[const_stack_top+z+1]].uses -= 1; \
     } while(0)
 
+#define CONST_GET(i) (PyList_GET_ITEM((consts), (i)))
+
 /* Scans back N consecutive LOAD_CONST instructions, skipping NOPs,
    returns index of the Nth last's LOAD_CONST's EXTENDED_ARG prefix.
    Callers are responsible to check CONST_STACK_LEN beforehand.
@@ -179,7 +207,7 @@
 static Py_ssize_t
 fold_tuple_on_constants(_Py_CODEUNIT *codestr, Py_ssize_t c_start,
                         Py_ssize_t opcode_end, unsigned char opcode,
-                        PyObject *consts, PyObject **objs, int n)
+                        PyObject *consts, unsigned int *const_ids, int n)
 {
     PyObject *newconst, *constant;
     Py_ssize_t i, len_consts;
@@ -193,7 +221,7 @@
         return -1;
     }
     for (i=0 ; i<n ; i++) {
-        constant = objs[i];
+        constant = CONST_GET(const_ids[i]);
         Py_INCREF(constant);
         PyTuple_SET_ITEM(newconst, i, constant);
     }
@@ -231,7 +259,7 @@
 static Py_ssize_t
 fold_binops_on_constants(_Py_CODEUNIT *codestr, Py_ssize_t c_start,
                          Py_ssize_t opcode_end, unsigned char opcode,
-                         PyObject *consts, PyObject **objs)
+                         PyObject *consts, unsigned int *const_ids)
 {
     PyObject *newconst, *v, *w;
     Py_ssize_t len_consts, size;
@@ -241,8 +269,8 @@
     len_consts = PyList_GET_SIZE(consts);
 
     /* Create new constant */
-    v = objs[0];
-    w = objs[1];
+    v = CONST_GET(const_ids[0]);
+    w = CONST_GET(const_ids[1]);
     switch (opcode) {
         case BINARY_POWER:
             newconst = PyNumber_Power(v, w, Py_None);
@@ -320,7 +348,7 @@
 static Py_ssize_t
 fold_unaryops_on_constants(_Py_CODEUNIT *codestr, Py_ssize_t c_start,
                            Py_ssize_t opcode_end, unsigned char opcode,
-                           PyObject *consts, PyObject *v)
+                           PyObject *consts, unsigned int const_idx)
 {
     PyObject *newconst;
     Py_ssize_t len_consts;
@@ -328,6 +356,7 @@
     /* Pre-conditions */
     assert(PyList_CheckExact(consts));
     len_consts = PyList_GET_SIZE(consts);
+    PyObject *v = CONST_GET(const_idx);
 
     /* Create new constant */
     switch (opcode) {
@@ -432,9 +461,12 @@
     unsigned char *lnotab;
     unsigned int cum_orig_offset, last_offset;
     Py_ssize_t tabsiz;
-    PyObject **const_stack = NULL;
+    unsigned int *const_stack = NULL;
     Py_ssize_t const_stack_top = -1;
     Py_ssize_t const_stack_size = 0;
+    struct const_uses_entry *const_uses = NULL;
+    Py_ssize_t const_uses_curr_size = 0;
+    Py_ssize_t const_uses_size = 0;
     int in_consts = 0;  /* whether we are in a LOAD_CONST sequence */
     unsigned int *blocks = NULL;
 
@@ -737,7 +769,34 @@
         last_offset = new_offset;
     }
 
-    /* Remove NOPs and fixup jump targets */
+    assert(PyList_GET_SIZE(consts) == const_uses_curr_size);
+
+    /* move used consts to the front of the list; remove unused
+       we skip the first const since it's either
+       - a string which will later become a docstring
+       - something else - unfortunately we can't remove it, since it could
+         move a string to the first cell and thus make it a docstring
+    */
+    const_uses[0].relocation = 0;
+    unsigned int relocation = 1;
+    for (int i = 1; i < const_uses_curr_size; ++i) {
+        PyObject *item = PyList_GET_ITEM(consts, i);
+        if (const_uses[i].uses == 0) {
+            Py_DECREF(item);
+            continue;
+        }
+        const_uses[i].relocation = relocation;
+        PyList_SET_ITEM(consts, relocation, item);
+        relocation++;
+    }
+    for (int i = relocation; i < const_uses_curr_size; ++i)
+        PyList_SET_ITEM(consts, i, NULL);
+
+    /* shrink consts as needed */
+    if (PyList_SetSlice(consts, relocation, const_uses_curr_size, NULL) < 0)
+        goto exitError;
+
+    /* Remove NOPs, fixup jump targets and LOAD_CONST args */
     for (op_start = i = h = 0; i < codelen; i++, op_start = i) {
         j = _Py_OPARG(codestr[i]);
         while (_Py_OPCODE(codestr[i]) == EXTENDED_ARG) {
@@ -748,6 +807,10 @@
         switch (opcode) {
             case NOP:continue;
 
+            case LOAD_CONST:
+                j = const_uses[j].relocation;
+                break;
+
             case JUMP_ABSOLUTE:
             case CONTINUE_LOOP:
             case POP_JUMP_IF_FALSE: