From a44b95cd574ecab4a4c41c6380c82db6029ad114 Mon Sep 17 00:00:00 2001 From: Ian Romanick Date: Mon, 16 Mar 2015 12:14:10 -0700 Subject: [PATCH] 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 Reviewed-by: Matt Turner --- 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) -- 2.7.4