Old habits die hard... I still just use LA 1,256 although now I might just code it as LA 1,256(,0)
:) Notice in the example where there was a USING 0,9 that the assembler ends up choosing the highest numbered register (9 versus 0 in this case) when more than one USING is in effect *and* the displacement would be the same - that is why R9 is picked over the implied USING of "register" zero... - working as designed. On Fri, 8 Nov 2019 at 17:49, Charles Mills <charl...@mcn.org> wrote: > 1.. Wow. I did not know that, and I have been coding S/360 and follow-ons > assembler since 1968. That would be an obscure bug-introducer. > > 2. I would argue that the preferred way (now -- not in 1968!) of loading a > constant 256 into R2 is LHI R2,256. Avoids the problem below, is arguable\y > more straightforward (no "address" anywhere in the picture) and might be > faster on some machines. > > Charles > > > -----Original Message----- > From: IBM Mainframe Assembler List [mailto:ASSEMBLER-LIST@LISTSERV.UGA.EDU] > On Behalf Of Bob Raicer > Sent: Friday, November 8, 2019 1:15 PM > To: ASSEMBLER-LIST@LISTSERV.UGA.EDU > Subject: Re: Questionable Instructions in Obtaining EAX documentation > > Well, the statement from Peter Relson (and others) which is > essentially: > ---------- > LA R1,1 is exactly equivalent to LA R1,1(0). Just look at the > generated object code. > ---------- > is not totally true. It all depends upon which USINGs are in effect. > > Take a peek at the following example (admittedly a bit unusual, but > perfectly legitimate). > > Loc Object Code Addr1 Addr2 Stmt Source Statement > 00000000 00000000 00000008 1 EXAMPLE CSECT , > R:9 00000000 2 USING 0,9 > 00000000 4120 9100 00000100 3 LA 2,256 > 00000004 4120 0100 00000100 4 LA 2,256(,0) > 5 END , > > If the intent is to place a truly non-relocatable value (e.g., a > constant) into a GPR (which IS the intent of this example), then I > believe the coding style of statement 4 is the preferred way to go; it > is explicit and unambiguous. This applies to many other instructions > which use base+displacement operands (examples: SLL, SRL, SLDL) > which are not interpreted as address values. >
