231159 2021-10-04 02:29:12 -0700 [JSC][ARMv7] Improve instruction selection in MacroAssembler 2022-03-24 03:34:21 -0700 1 1 1 Unclassified WebKit JavaScriptCore WebKit Nightly Build Unspecified Unspecified RESOLVED FIXED InRadar P2 Normal --- 1 glore webkit-unassigned guijemont mikhail webkit-bug-importer xan.lopez oldest_to_newest 1799999 0 glore 2021-10-04 02:29:12 -0700 I have spotted some improvement opportunities in MacroAssemblerARMv7 for better instruction selection for some macros. What shows up most often in the disassembly ('ip' is 'r12'): mvn ip, #8 and r0, r0, ip This is an 8-byte sequence which is equivalent to the following 2-byte instruction: bic r0, #8 similarly: mvn ip, #7 add r0, r0, ip should be: sub r0, r0, #8 A review of the disassembly would likely yield more examples of similar sequences where an immediate can be encoded cheaper using an alternative instruction. 1801110 1 guijemont 2021-10-06 08:53:32 -0700 (In reply to Geza Lore from comment #0) > I have spotted some improvement opportunities in MacroAssemblerARMv7 for > better instruction selection for some macros. What shows up most often in > the disassembly ('ip' is 'r12'): > > mvn ip, #8 > and r0, r0, ip > > This is an 8-byte sequence which is equivalent to the following 2-byte > instruction: > > bic r0, #8 > > > similarly: > > mvn ip, #7 > add r0, r0, ip > > should be: > > sub r0, r0, #8 > > A review of the disassembly would likely yield more examples of similar > sequences where an immediate can be encoded cheaper using an alternative > instruction. Would any of this change the minimal version of the instruction set that we support? (not that I have it very clear in my mind what is our minimum currently). 1801136 2 glore 2021-10-06 09:32:00 -0700 Not these. BIC and SUB are as old as AND and ADD. 1802558 3 webkit-bug-importer 2021-10-11 02:30:20 -0700 <rdar://problem/84091839> 1818711 4 glore 2021-11-30 07:21:03 -0800 Note https://bugs.webkit.org/show_bug.cgi?id=233474 implements the most frequent case of the mentioned add/sub exchange. 1854642 5 glore 2022-03-24 03:34:21 -0700 These have now been implemented in various patches