[Mesa-dev] [PATCH 05/19] i965/fs: Loop from 0 to inst->sources, not 0 to 3.

[Kenneth Graunke]

On Monday, June 02, 2014 03:48:23 PM Ian Romanick wrote:
> On 05/31/2014 10:11 PM, Kenneth Graunke wrote:
> > On Tuesday, May 27, 2014 06:47:36 PM Matt Turner wrote:
> > [snip]
> >> diff --git a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp 
> > b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> >> index 069b60f..a1aff21 100644
> >> --- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> >> +++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> >> @@ -353,7 +353,7 @@ fs_visitor::try_constant_propagate(fs_inst *inst, 
> > acp_entry *entry)
> >>     if (entry->src.file != IMM)
> >>        return false;
> >>  
> >> -   for (int i = 2; i >= 0; i--) {
> >> +   for (int i = inst->sources - 1; i >= 0; i--) {
> >>        if (inst->src[i].file != entry->dst.file ||
> >>            inst->src[i].reg != entry->dst.reg ||
> >>            inst->src[i].reg_offset != entry->dst.reg_offset ||
> > 
> > I am glad to see that you're using a signed integer type here.  For 
> > BRW_OPCODE_NOP, SHADER_OPCODE_PLACEHOLDER_HALT, and so on, inst->sources 
could 
> > conceievably be 0.  (Today, you set it to 3 for some reason, but I could 
see 
> > someone coming along and "fixing" that later...)
> > 
> > If you had used unsigned types, this would translate into i = 4294967296; 
i >= 
> > 0; i--, which would take forever.  With signed types, it works, and no one 
> > should get bitten by that bug.
> 
> Consistency of types is good.  Some folks build with additional
> warnings, and the flood of
> 
> main/bufferobj.c:2855:18: warning: comparison between signed and unsigned 
integer expressions [-Wsign-compare]
> 
> can hide legit bugs. :(

I'm not advocating against leaving compiler warnings.  I'm advocating against 
naively changing it to unsigned in order to "shut up" those warnings, and 
actually /introduce/ bugs.

Here, the right solution is probably to use a signed counter, and explicitly 
cast uint -> int to shut up the compiler.

--Ken
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 836 bytes
Desc: This is a digitally signed message part.
URL: <http://lists.freedesktop.org/archives/mesa-dev/attachments/20140602/154a5646/attachment-0001.sig>