Backport r69961 to trunk, replacing JUMP_IF_{TRUE,FALSE} with

POP_JUMP_IF_{TRUE,FALSE} and JUMP_IF_{TRUE,FALSE}_OR_POP. This avoids executing
a POP_TOP on each conditional and sometimes allows the peephole optimizer to
skip a JUMP_ABSOLUTE entirely. It speeds up list comprehensions significantly.

1 files changed, 33 insertions, 53 deletions

diff --git a/Python/compile.c b/Python/compile.c
index a252bd15f1..69321ae0c4 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -836,11 +836,15 @@ opcode_stack_effect(int opcode, int oparg)
 			return 1;
 
 		case JUMP_FORWARD:
-		case JUMP_IF_FALSE:
-		case JUMP_IF_TRUE:
+		case JUMP_IF_TRUE_OR_POP:  /* -1 if jump not taken */
+		case JUMP_IF_FALSE_OR_POP:  /*  "" */
 		case JUMP_ABSOLUTE:
 			return 0;
 
+		case POP_JUMP_IF_FALSE:
+		case POP_JUMP_IF_TRUE:
+			return -1;
+
 		case LOAD_GLOBAL:
 			return 1;
 
@@ -1499,12 +1503,10 @@ compiler_ifexp(struct compiler *c, expr_ty e)
 	if (next == NULL)
 		return 0;
 	VISIT(c, expr, e->v.IfExp.test);
-	ADDOP_JREL(c, JUMP_IF_FALSE, next);
-	ADDOP(c, POP_TOP);
+	ADDOP_JABS(c, POP_JUMP_IF_FALSE, next);
 	VISIT(c, expr, e->v.IfExp.body);
 	ADDOP_JREL(c, JUMP_FORWARD, end);
 	compiler_use_next_block(c, next);
-	ADDOP(c, POP_TOP);
 	VISIT(c, expr, e->v.IfExp.orelse);
 	compiler_use_next_block(c, end);
 	return 1;
@@ -1597,9 +1599,6 @@ compiler_if(struct compiler *c, stmt_ty s)
 	end = compiler_new_block(c);
 	if (end == NULL)
 		return 0;
-	next = compiler_new_block(c);
-	if (next == NULL)
-	    return 0;
 	
 	constant = expr_constant(s->v.If.test);
 	/* constant = 0: "if 0"
@@ -1611,15 +1610,21 @@ compiler_if(struct compiler *c, stmt_ty s)
 	} else if (constant == 1) {
 		VISIT_SEQ(c, stmt, s->v.If.body);
 	} else {
+		if (s->v.If.orelse) {
+			next = compiler_new_block(c);
+			if (next == NULL)
+			    return 0;
+		}
+		else
+			next = end;
 		VISIT(c, expr, s->v.If.test);
-		ADDOP_JREL(c, JUMP_IF_FALSE, next);
-		ADDOP(c, POP_TOP);
+		ADDOP_JABS(c, POP_JUMP_IF_FALSE, next);
 		VISIT_SEQ(c, stmt, s->v.If.body);
 		ADDOP_JREL(c, JUMP_FORWARD, end);
-		compiler_use_next_block(c, next);
-		ADDOP(c, POP_TOP);
-		if (s->v.If.orelse)
+		if (s->v.If.orelse) {
+			compiler_use_next_block(c, next);
 			VISIT_SEQ(c, stmt, s->v.If.orelse);
+		}
 	}
 	compiler_use_next_block(c, end);
 	return 1;
@@ -1693,8 +1698,7 @@ compiler_while(struct compiler *c, stmt_ty s)
 		   so we need to set an extra line number. */
 		c->u->u_lineno_set = false;
 		VISIT(c, expr, s->v.While.test);
-		ADDOP_JREL(c, JUMP_IF_FALSE, anchor);
-		ADDOP(c, POP_TOP);
+		ADDOP_JABS(c, POP_JUMP_IF_FALSE, anchor);
 	}
 	VISIT_SEQ(c, stmt, s->v.While.body);
 	ADDOP_JABS(c, JUMP_ABSOLUTE, loop);
@@ -1705,7 +1709,6 @@ compiler_while(struct compiler *c, stmt_ty s)
 
 	if (constant == -1) {
 		compiler_use_next_block(c, anchor);
-		ADDOP(c, POP_TOP);
 		ADDOP(c, POP_BLOCK);
 	}
 	compiler_pop_fblock(c, LOOP, loop);
@@ -1826,20 +1829,17 @@ compiler_try_finally(struct compiler *c, stmt_ty s)
    [tb, val, exc]	L1:	DUP				)
    [tb, val, exc, exc]		<evaluate E1>			)
    [tb, val, exc, exc, E1]	COMPARE_OP	EXC_MATCH	) only if E1
-   [tb, val, exc, 1-or-0]	JUMP_IF_FALSE	L2		)
-   [tb, val, exc, 1]		POP				)
+   [tb, val, exc, 1-or-0]	POP_JUMP_IF_FALSE	L2	)
    [tb, val, exc]		POP
    [tb, val]			<assign to V1>	(or POP if no V1)
    [tb]				POP
    []				<code for S1>
 				JUMP_FORWARD	L0
    
-   [tb, val, exc, 0]	L2:	POP
-   [tb, val, exc]		DUP
+   [tb, val, exc]	L2:	DUP
    .............................etc.......................
 
-   [tb, val, exc, 0]	Ln+1:	POP
-   [tb, val, exc]		END_FINALLY	# re-raise exception
+   [tb, val, exc]	Ln+1:	END_FINALLY	# re-raise exception
    
    []			L0:	<next statement>
    
@@ -1881,8 +1881,7 @@ compiler_try_except(struct compiler *c, stmt_ty s)
 			ADDOP(c, DUP_TOP);
 			VISIT(c, expr, handler->v.ExceptHandler.type);
 			ADDOP_I(c, COMPARE_OP, PyCmp_EXC_MATCH);
-			ADDOP_JREL(c, JUMP_IF_FALSE, except);
-			ADDOP(c, POP_TOP);
+			ADDOP_JABS(c, POP_JUMP_IF_FALSE, except);
 		}
 		ADDOP(c, POP_TOP);
 		if (handler->v.ExceptHandler.name) {
@@ -1895,8 +1894,6 @@ compiler_try_except(struct compiler *c, stmt_ty s)
 		VISIT_SEQ(c, stmt, handler->v.ExceptHandler.body);
 		ADDOP_JREL(c, JUMP_FORWARD, end);
 		compiler_use_next_block(c, except);
-		if (handler->v.ExceptHandler.type)
-			ADDOP(c, POP_TOP);
 	}
 	ADDOP(c, END_FINALLY);
 	compiler_use_next_block(c, orelse);
@@ -2084,8 +2081,7 @@ compiler_assert(struct compiler *c, stmt_ty s)
 	end = compiler_new_block(c);
 	if (end == NULL)
 		return 0;
-	ADDOP_JREL(c, JUMP_IF_TRUE, end);
-	ADDOP(c, POP_TOP);
+	ADDOP_JABS(c, POP_JUMP_IF_TRUE, end);
 	ADDOP_O(c, LOAD_GLOBAL, assertion_error, names);
 	if (s->v.Assert.msg) {
 		VISIT(c, expr, s->v.Assert.msg);
@@ -2095,7 +2091,6 @@ compiler_assert(struct compiler *c, stmt_ty s)
 		ADDOP_I(c, RAISE_VARARGS, 1);
 	}
 	compiler_use_next_block(c, end);
-	ADDOP(c, POP_TOP);
 	return 1;
 }
 
@@ -2473,9 +2468,9 @@ compiler_boolop(struct compiler *c, expr_ty e)
 
 	assert(e->kind == BoolOp_kind);
 	if (e->v.BoolOp.op == And)
-		jumpi = JUMP_IF_FALSE;
+		jumpi = JUMP_IF_FALSE_OR_POP;
 	else
-		jumpi = JUMP_IF_TRUE;
+		jumpi = JUMP_IF_TRUE_OR_POP;
 	end = compiler_new_block(c);
 	if (end == NULL)
 		return 0;
@@ -2484,8 +2479,7 @@ compiler_boolop(struct compiler *c, expr_ty e)
 	assert(n >= 0);
 	for (i = 0; i < n; ++i) {
 		VISIT(c, expr, (expr_ty)asdl_seq_GET(s, i));
-		ADDOP_JREL(c, jumpi, end);
-		ADDOP(c, POP_TOP)
+		ADDOP_JABS(c, jumpi, end);
 	}
 	VISIT(c, expr, (expr_ty)asdl_seq_GET(s, n));
 	compiler_use_next_block(c, end);
@@ -2543,9 +2537,8 @@ compiler_compare(struct compiler *c, expr_ty e)
 		ADDOP_I(c, COMPARE_OP,
 			cmpop((cmpop_ty)(asdl_seq_GET(
 						  e->v.Compare.ops, i - 1))));
-		ADDOP_JREL(c, JUMP_IF_FALSE, cleanup);
+		ADDOP_JABS(c, JUMP_IF_FALSE_OR_POP, cleanup);
 		NEXT_BLOCK(c);
-		ADDOP(c, POP_TOP);
 		if (i < (n - 1))
 		    VISIT(c, expr, 
 			    (expr_ty)asdl_seq_GET(e->v.Compare.comparators, i));
@@ -2636,9 +2629,8 @@ compiler_listcomp_generator(struct compiler *c, asdl_seq *generators,
 	for (i = 0; i < n; i++) {
 		expr_ty e = (expr_ty)asdl_seq_GET(l->ifs, i);
 		VISIT(c, expr, e);
-		ADDOP_JREL(c, JUMP_IF_FALSE, if_cleanup);
+		ADDOP_JABS(c, POP_JUMP_IF_FALSE, if_cleanup);
 		NEXT_BLOCK(c);
-		ADDOP(c, POP_TOP);
 	} 
 
 	if (++gen_index < asdl_seq_LEN(generators))
@@ -2652,12 +2644,7 @@ compiler_listcomp_generator(struct compiler *c, asdl_seq *generators,
 
 	    compiler_use_next_block(c, skip);
 	}
-	for (i = 0; i < n; i++) {
-		ADDOP_I(c, JUMP_FORWARD, 1);
-		if (i == 0)
-		    compiler_use_next_block(c, if_cleanup);
-		ADDOP(c, POP_TOP);
-	} 
+	compiler_use_next_block(c, if_cleanup);
 	ADDOP_JABS(c, JUMP_ABSOLUTE, start);
 	compiler_use_next_block(c, anchor);
 	
@@ -2720,10 +2707,9 @@ compiler_genexp_generator(struct compiler *c,
 	for (i = 0; i < n; i++) {
 		expr_ty e = (expr_ty)asdl_seq_GET(ge->ifs, i);
 		VISIT(c, expr, e);
-		ADDOP_JREL(c, JUMP_IF_FALSE, if_cleanup);
+		ADDOP_JABS(c, POP_JUMP_IF_FALSE, if_cleanup);
 		NEXT_BLOCK(c);
-		ADDOP(c, POP_TOP);
-	} 
+	}
 
 	if (++gen_index < asdl_seq_LEN(generators))
 		if (!compiler_genexp_generator(c, generators, gen_index, elt))
@@ -2737,13 +2723,7 @@ compiler_genexp_generator(struct compiler *c,
 
 		compiler_use_next_block(c, skip);
 	}
-	for (i = 0; i < n; i++) {
-		ADDOP_I(c, JUMP_FORWARD, 1);
-		if (i == 0)
-			compiler_use_next_block(c, if_cleanup);
-
-		ADDOP(c, POP_TOP);
-	} 
+	compiler_use_next_block(c, if_cleanup);
 	ADDOP_JABS(c, JUMP_ABSOLUTE, start);
 	compiler_use_next_block(c, anchor);
 	ADDOP(c, POP_BLOCK);