On Wed, May 4, 2016 at 4:20 PM, Wilco Dijkstra <wilco.dijks...@arm.com> wrote: > Bernd Schmidt wrote: >> On 05/04/2016 03:25 PM, Ramana Radhakrishnan wrote: >>> On ARM / AArch32 I haven't seen any performance data yet - the one place we >>> are concerned >>> about the impact is on Thumb2 code size as regrename may end up >>> inadvertently putting more >>> things in high registers. >> >> In theory at least arm_preferred_rename_class is designed to make the >> opposite happen. Bernd > > I do not see that working unfortunately - Thumb-2 codesize increases by a few > percent even with -Os. > This is primarily due to replacing a low register with IP, which often > changes a 16-bit instruction like: > > movs r2, #8 > > into a 32-bit one: > > mov ip, #8 > > This will also affect other targets with multiple instruction sizes. So I > think it should check the > size of the new instruction patterns and only accept a rename if it is not > larger (certainly with -Os).
Can you file a bugzilla entry with a testcase that folks can look at please ? Ramana >
