gh-106149: move jump target resolution from optimizer to assembler (#106150)

Author: iritkatriel

Include/internal/pycore_compile.h

@@ -28,7 +28,7 @@ extern int _PyAST_Optimize(
     int ff_features);
 
 typedef struct {
-    int h_offset;
+    int h_label;
     int h_startdepth;
     int h_preserve_lasti;
 } _PyCompile_ExceptHandlerInfo;
@@ -38,6 +38,10 @@ typedef struct {
     int i_oparg;
     _PyCompilerSrcLocation i_loc;
     _PyCompile_ExceptHandlerInfo i_except_handler_info;
+
+    /* Used by the assembler */
+    int i_target;
+    int i_offset;
 } _PyCompile_Instruction;
 
 typedef struct {
@@ -85,8 +89,6 @@ int _PyCompile_EnsureArrayLargeEnough(
 
 int _PyCompile_ConstCacheMergeOne(PyObject *const_cache, PyObject **obj);
 
-int _PyCompile_InstrSize(int opcode, int oparg);
-
 /* Access compiler internals for unit testing */
 
 PyAPI_FUNC(PyObject*) _PyCompile_CodeGen(

Include/internal/pycore_flowgraph.h

@@ -55,8 +55,6 @@ typedef struct _PyCfgBasicblock_ {
     int b_predecessors;
     /* depth of stack upon entry of block, computed by stackdepth() */
     int b_startdepth;
-    /* instruction offset for block, computed by assemble_jump_offsets() */
-    int b_offset;
     /* Basic block is an exception handler that preserves lasti */
     unsigned b_preserve_lasti : 1;
     /* Used by compiler passes to mark whether they have visited a basic block. */

Python/assemble.c

@@ -4,6 +4,7 @@
 #include "pycore_code.h"          // write_location_entry_start()
 #include "pycore_compile.h"
 #include "pycore_opcode.h"        // _PyOpcode_Caches[] and opcode category macros
+#include "pycore_opcode_utils.h"  // IS_BACKWARDS_JUMP_OPCODE
 #include "opcode_metadata.h"      // IS_PSEUDO_INSTR
 
 
@@ -34,6 +35,18 @@ same_location(location a, location b)
            a.end_col_offset == b.end_col_offset;
 }
 
+static int
+instr_size(instruction *instr)
+{
+    int opcode = instr->i_opcode;
+    int oparg = instr->i_oparg;
+    assert(!IS_PSEUDO_INSTR(opcode));
+    assert(OPCODE_HAS_ARG(opcode) || oparg == 0);
+    int extended_args = (0xFFFFFF < oparg) + (0xFFFF < oparg) + (0xFF < oparg);
+    int caches = _PyOpcode_Caches[opcode];
+    return extended_args + 1 + caches;
+}
+
 struct assembler {
     PyObject *a_bytecode;  /* bytes containing bytecode */
     int a_offset;              /* offset into bytecode */
@@ -118,6 +131,7 @@ assemble_emit_exception_table_item(struct assembler *a, int value, int msb)
 
 static int
 assemble_emit_exception_table_entry(struct assembler *a, int start, int end,
+                                    int handler_offset,
                                     _PyCompile_ExceptHandlerInfo *handler)
 {
     Py_ssize_t len = PyBytes_GET_SIZE(a->a_except_table);
@@ -126,7 +140,7 @@ assemble_emit_exception_table_entry(struct assembler *a, int start, int end,
     }
     int size = end-start;
     assert(end > start);
-    int target = handler->h_offset;
+    int target = handler_offset;
     int depth = handler->h_startdepth - 1;
     if (handler->h_preserve_lasti > 0) {
         depth -= 1;
@@ -145,24 +159,30 @@ assemble_exception_table(struct assembler *a, instr_sequence *instrs)
 {
     int ioffset = 0;
     _PyCompile_ExceptHandlerInfo handler;
-    handler.h_offset = -1;
+    handler.h_label = -1;
     handler.h_startdepth = -1;
     handler.h_preserve_lasti = -1;
     int start = -1;
     for (int i = 0; i < instrs->s_used; i++) {
         instruction *instr = &instrs->s_instrs[i];
-        if (instr->i_except_handler_info.h_offset != handler.h_offset) {
-            if (handler.h_offset >= 0) {
+        if (instr->i_except_handler_info.h_label != handler.h_label) {
+            if (handler.h_label >= 0) {
+                int handler_offset = instrs->s_instrs[handler.h_label].i_offset;
                 RETURN_IF_ERROR(
-                    assemble_emit_exception_table_entry(a, start, ioffset, &handler));
+                    assemble_emit_exception_table_entry(a, start, ioffset,
+                                                        handler_offset,
+                                                        &handler));
             }
             start = ioffset;
             handler = instr->i_except_handler_info;
         }
-        ioffset += _PyCompile_InstrSize(instr->i_opcode, instr->i_oparg);
+        ioffset += instr_size(instr);
     }
-    if (handler.h_offset >= 0) {
-        RETURN_IF_ERROR(assemble_emit_exception_table_entry(a, start, ioffset, &handler));
+    if (handler.h_label >= 0) {
+        int handler_offset = instrs->s_instrs[handler.h_label].i_offset;
+        RETURN_IF_ERROR(assemble_emit_exception_table_entry(a, start, ioffset,
+                                                            handler_offset,
+                                                            &handler));
     }
     return SUCCESS;
 }
@@ -329,7 +349,7 @@ assemble_location_info(struct assembler *a, instr_sequence *instrs,
                 loc = instr->i_loc;
                 size = 0;
         }
-        size += _PyCompile_InstrSize(instr->i_opcode, instr->i_oparg);
+        size += instr_size(instr);
     }
     RETURN_IF_ERROR(assemble_emit_location(a, loc, size));
     return SUCCESS;
@@ -385,7 +405,7 @@ assemble_emit_instr(struct assembler *a, instruction *instr)
     Py_ssize_t len = PyBytes_GET_SIZE(a->a_bytecode);
     _Py_CODEUNIT *code;
 
-    int size = _PyCompile_InstrSize(instr->i_opcode, instr->i_oparg);
+    int size = instr_size(instr);
     if (a->a_offset + size >= len / (int)sizeof(_Py_CODEUNIT)) {
         if (len > PY_SSIZE_T_MAX / 2) {
             return ERROR;
@@ -585,12 +605,83 @@ makecode(_PyCompile_CodeUnitMetadata *umd, struct assembler *a, PyObject *const_
     return co;
 }
 
+static int
+resolve_jump_offsets(instr_sequence *instrs)
+{
+    /* Compute the size of each instruction and fixup jump args.
+     * Replace instruction index with position in bytecode.
+     */
+
+    for (int i = 0; i < instrs->s_used; i++) {
+        instruction *instr = &instrs->s_instrs[i];
+        if (OPCODE_HAS_JUMP(instr->i_opcode)) {
+            instr->i_target = instr->i_oparg;
+        }
+    }
+
+    int extended_arg_recompile;
+
+    do {
+        int totsize = 0;
+        for (int i = 0; i < instrs->s_used; i++) {
+            instruction *instr = &instrs->s_instrs[i];
+            instr->i_offset = totsize;
+            int isize = instr_size(instr);
+            totsize += isize;
+        }
+        extended_arg_recompile = 0;
+
+        int offset = 0;
+        for (int i = 0; i < instrs->s_used; i++) {
+            instruction *instr = &instrs->s_instrs[i];
+            int isize = instr_size(instr);
+            /* jump offsets are computed relative to
+             * the instruction pointer after fetching
+             * the jump instruction.
+             */
+            offset += isize;
+            if (OPCODE_HAS_JUMP(instr->i_opcode)) {
+                instruction *target = &instrs->s_instrs[instr->i_target];
+                instr->i_oparg = target->i_offset;
+                if (instr->i_oparg < offset) {
+                    assert(IS_BACKWARDS_JUMP_OPCODE(instr->i_opcode));
+                    instr->i_oparg = offset - instr->i_oparg;
+                }
+                else {
+                    assert(!IS_BACKWARDS_JUMP_OPCODE(instr->i_opcode));
+                    instr->i_oparg = instr->i_oparg - offset;
+                }
+                if (instr_size(instr) != isize) {
+                    extended_arg_recompile = 1;
+                }
+            }
+        }
+    /* XXX: This is an awful hack that could hurt performance, but
+        on the bright side it should work until we come up
+        with a better solution.
+
+        The issue is that in the first loop instr_size() is
+        called, and it requires i_oparg be set appropriately.
+        There is a bootstrap problem because i_oparg is
+        calculated in the second loop above.
+
+        So we loop until we stop seeing new EXTENDED_ARGs.
+        The only EXTENDED_ARGs that could be popping up are
+        ones in jump instructions.  So this should converge
+        fairly quickly.
+    */
+    } while (extended_arg_recompile);
+    return SUCCESS;
+}
 
 PyCodeObject *
 _PyAssemble_MakeCodeObject(_PyCompile_CodeUnitMetadata *umd, PyObject *const_cache,
                            PyObject *consts, int maxdepth, instr_sequence *instrs,
                            int nlocalsplus, int code_flags, PyObject *filename)
 {
+    if (resolve_jump_offsets(instrs) < 0) {
+        return NULL;
+    }
     PyCodeObject *co = NULL;
 
     struct assembler a;

Python/compile.c

@@ -131,16 +131,6 @@ enum {
 };
 
 
-int
-_PyCompile_InstrSize(int opcode, int oparg)
-{
-    assert(!IS_PSEUDO_INSTR(opcode));
-    assert(OPCODE_HAS_ARG(opcode) || oparg == 0);
-    int extended_args = (0xFFFFFF < oparg) + (0xFFFF < oparg) + (0xFF < oparg);
-    int caches = _PyOpcode_Caches[opcode];
-    return extended_args + 1 + caches;
-}
-
 typedef _PyCompile_Instruction instruction;
 typedef _PyCompile_InstructionSequence instr_sequence;
 
@@ -7717,17 +7707,20 @@ cfg_to_instr_sequence(cfg_builder *g, instr_sequence *seq)
         RETURN_IF_ERROR(instr_sequence_use_label(seq, b->b_label.id));
         for (int i = 0; i < b->b_iused; i++) {
             cfg_instr *instr = &b->b_instr[i];
+            if (OPCODE_HAS_JUMP(instr->i_opcode)) {
+                instr->i_oparg = instr->i_target->b_label.id;
+            }
             RETURN_IF_ERROR(
                 instr_sequence_addop(seq, instr->i_opcode, instr->i_oparg, instr->i_loc));
 
             _PyCompile_ExceptHandlerInfo *hi = &seq->s_instrs[seq->s_used-1].i_except_handler_info;
             if (instr->i_except != NULL) {
-                hi->h_offset = instr->i_except->b_offset;
+                hi->h_label = instr->i_except->b_label.id;
                 hi->h_startdepth = instr->i_except->b_startdepth;
                 hi->h_preserve_lasti = instr->i_except->b_preserve_lasti;
             }
             else {
-                hi->h_offset = -1;
+                hi->h_label = -1;
             }
         }
     }

Python/flowgraph.c

@@ -166,22 +166,6 @@ _PyBasicblock_InsertInstruction(basicblock *block, int pos, cfg_instr *instr) {
     return SUCCESS;
 }
 
-static int
-instr_size(cfg_instr *instruction)
-{
-    return _PyCompile_InstrSize(instruction->i_opcode, instruction->i_oparg);
-}
-
-static int
-blocksize(basicblock *b)
-{
-    int size = 0;
-    for (int i = 0; i < b->b_iused; i++) {
-        size += instr_size(&b->b_instr[i]);
-    }
-    return size;
-}
-
 /* For debugging purposes only */
 #if 0
 static void
@@ -212,9 +196,9 @@ static void
 dump_basicblock(const basicblock *b)
 {
     const char *b_return = basicblock_returns(b) ? "return " : "";
-    fprintf(stderr, "%d: [EH=%d CLD=%d WRM=%d NO_FT=%d %p] used: %d, depth: %d, offset: %d %s\n",
+    fprintf(stderr, "%d: [EH=%d CLD=%d WRM=%d NO_FT=%d %p] used: %d, depth: %d, %s\n",
         b->b_label.id, b->b_except_handler, b->b_cold, b->b_warm, BB_NO_FALLTHROUGH(b), b, b->b_iused,
-        b->b_startdepth, b->b_offset, b_return);
+        b->b_startdepth, b_return);
     if (b->b_instr) {
         int i;
         for (i = 0; i < b->b_iused; i++) {
@@ -480,71 +464,11 @@ normalize_jumps(_PyCfgBuilder *g)
     return SUCCESS;
 }
 
-static void
-resolve_jump_offsets(basicblock *entryblock)
-{
-    int bsize, totsize, extended_arg_recompile;
-
-    /* Compute the size of each block and fixup jump args.
-       Replace block pointer with position in bytecode. */
-    do {
-        totsize = 0;
-        for (basicblock *b = entryblock; b != NULL; b = b->b_next) {
-            bsize = blocksize(b);
-            b->b_offset = totsize;
-            totsize += bsize;
-        }
-        extended_arg_recompile = 0;
-        for (basicblock *b = entryblock; b != NULL; b = b->b_next) {
-            bsize = b->b_offset;
-            for (int i = 0; i < b->b_iused; i++) {
-                cfg_instr *instr = &b->b_instr[i];
-                int isize = instr_size(instr);
-                /* jump offsets are computed relative to
-                 * the instruction pointer after fetching
-                 * the jump instruction.
-                 */
-                bsize += isize;
-                if (is_jump(instr)) {
-                    instr->i_oparg = instr->i_target->b_offset;
-                    if (instr->i_oparg < bsize) {
-                        assert(IS_BACKWARDS_JUMP_OPCODE(instr->i_opcode));
-                        instr->i_oparg = bsize - instr->i_oparg;
-                    }
-                    else {
-                        assert(!IS_BACKWARDS_JUMP_OPCODE(instr->i_opcode));
-                        instr->i_oparg -= bsize;
-                    }
-                    if (instr_size(instr) != isize) {
-                        extended_arg_recompile = 1;
-                    }
-                }
-            }
-        }
-
-    /* XXX: This is an awful hack that could hurt performance, but
-        on the bright side it should work until we come up
-        with a better solution.
-
-        The issue is that in the first loop blocksize() is called
-        which calls instr_size() which requires i_oparg be set
-        appropriately. There is a bootstrap problem because
-        i_oparg is calculated in the second loop above.
-
-        So we loop until we stop seeing new EXTENDED_ARGs.
-        The only EXTENDED_ARGs that could be popping up are
-        ones in jump instructions.  So this should converge
-        fairly quickly.
-    */
-    } while (extended_arg_recompile);
-}
-
 int
 _PyCfg_ResolveJumps(_PyCfgBuilder *g)
 {
     RETURN_IF_ERROR(normalize_jumps(g));
     assert(no_redundant_jumps(g));
-    resolve_jump_offsets(g->g_entryblock);
     return SUCCESS;
 }