Issue #1754094: Improve the stack depth calculation in the compiler.

There should be no other effect than a small decrease in memory use.

diff --git a/Misc/NEWS b/Misc/NEWS
index 101487ac83a8549dd66851de8353dc24b0e6d161..4a82a5e879c582c4eb46ecca0777103b63337ebc 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,10 @@ What's New in Python 3.2 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #1754094: Improve the stack depth calculation in the compiler.
+  There should be no other effect than a small decrease in memory use.
+  Patch by Christopher Tur Lesniewski-Laas.
+
 - Issue #7065: Fix a crash in bytes.maketrans and bytearray.maketrans when
   using byte values greater than 127.  Patch by egreen.
 

diff --git a/Python/compile.c b/Python/compile.c
index 24975b64a76d7d80912738418931341127fcae7b..d06a03b907beddc3560372c2eb802fe09215f4f4 100644 (file)
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -772,7 +772,7 @@ opcode_stack_effect(int opcode, int oparg)
                case UNPACK_EX:
                        return (oparg&0xFF) + (oparg>>8);
                case FOR_ITER:
-                       return 1;
+                       return 1; /* or -1, at end of iterator */
 
                case STORE_ATTR:
                        return -2;
@@ -799,7 +799,7 @@ opcode_stack_effect(int opcode, int oparg)
                case COMPARE_OP:
                        return -1;
                case IMPORT_NAME:
-                       return 0;
+                       return -1;
                case IMPORT_FROM:
                        return 1;
 
@@ -3546,7 +3546,7 @@ dfs(struct compiler *c, basicblock *b, struct assembler *a)
 static int
 stackdepth_walk(struct compiler *c, basicblock *b, int depth, int maxdepth)
 {
-       int i;
+       int i, target_depth;
        struct instr *instr;
        if (b->b_seen || b->b_startdepth >= depth)
                return maxdepth;
@@ -3559,8 +3559,17 @@ stackdepth_walk(struct compiler *c, basicblock *b, int depth, int maxdepth)
                        maxdepth = depth;
                assert(depth >= 0); /* invalid code or bug in stackdepth() */
                if (instr->i_jrel || instr->i_jabs) {
+                       target_depth = depth;
+                       if (instr->i_opcode == FOR_ITER) {
+                               target_depth = depth-2;
+                       } else if (instr->i_opcode == SETUP_FINALLY ||
+                                  instr->i_opcode == SETUP_EXCEPT) {
+                               target_depth = depth+3;
+                               if (target_depth > maxdepth)
+                                       maxdepth = target_depth;
+                       }
                        maxdepth = stackdepth_walk(c, instr->i_target,
-                                                  depth, maxdepth);
+                                                  target_depth, maxdepth);
                        if (instr->i_opcode == JUMP_ABSOLUTE ||
                            instr->i_opcode == JUMP_FORWARD) {
                                goto out; /* remaining code is dead */