Mesa (master): glsl: Annotate as_foo functions that the this pointer cannot be NULL
Ian Romanick
idr at kemper.freedesktop.org
Thu Mar 19 22:37:14 UTC 2015
Module: Mesa
Branch: master
Commit: a44b95cd574ecab4a4c41c6380c82db6029ad114
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=a44b95cd574ecab4a4c41c6380c82db6029ad114
Author: Ian Romanick <ian.d.romanick at intel.com>
Date: Mon Mar 16 12:14:10 2015 -0700
glsl: Annotate as_foo functions that the this pointer cannot be NULL
We use the idiom
ir_foo *x = y->as_foo();
if (x == NULL)
return;
all over the place. GCC generates some quite lovely code for this.
One such example:
340a5b: 83 7d 18 04 cmpl $0x4,0x18(%rbp)
340a5f: 0f 85 06 04 00 00 jne 340e6b
340a65: 48 85 ed test %rbp,%rbp
340a68: 0f 84 fd 03 00 00 je 340e6b
This case used as_expression() (ir_type_expression is 4). Note that it
checks the ir_type, then checks that the pointer isn't NULL. There is
some disconnect in GCC around the condition in the as_foo functions.
return ir_type == ir_type_##TYPE ? (ir_##TYPE *) this : NULL; \
It believes "this" could be NULL, so it emits check outside the function
just for fun.
This patch uses assume() to tell GCC that it need not bother with extra
NULL checking of the pointer returned by the as_foo functions.
text data bss dec hex filename
4836430 158688 26248 5021366 4c9eb6 i965_dri-before.so
4836173 158688 26248 5021109 4c9db5 i965_dri-after.so
v2: Replace 'if (this == NULL) unreachable("this cannot be NULL")' with
assume(this != NULL). Suggested by Ilia Mirkin.
Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Reviewed-by: Matt Turner <mattst88 at gmail.com>
---
src/glsl/ir.h | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/src/glsl/ir.h b/src/glsl/ir.h
index 25f2eca..fdc22ed 100644
--- a/src/glsl/ir.h
+++ b/src/glsl/ir.h
@@ -119,6 +119,7 @@ public:
/*@{*/
class ir_rvalue *as_rvalue()
{
+ assume(this != NULL);
if (ir_type == ir_type_dereference_array ||
ir_type == ir_type_dereference_record ||
ir_type == ir_type_dereference_variable ||
@@ -132,6 +133,7 @@ public:
class ir_dereference *as_dereference()
{
+ assume(this != NULL);
if (ir_type == ir_type_dereference_array ||
ir_type == ir_type_dereference_record ||
ir_type == ir_type_dereference_variable)
@@ -141,6 +143,7 @@ public:
class ir_jump *as_jump()
{
+ assume(this != NULL);
if (ir_type == ir_type_loop_jump ||
ir_type == ir_type_return ||
ir_type == ir_type_discard)
@@ -151,6 +154,7 @@ public:
#define AS_CHILD(TYPE) \
class ir_##TYPE * as_##TYPE() \
{ \
+ assume(this != NULL); \
return ir_type == ir_type_##TYPE ? (ir_##TYPE *) this : NULL; \
}
AS_CHILD(variable)
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