570276 - Extra junk code generated for loading variable address on SPARC

Status: RESOLVED FIXED

(Tamarin Graveyard :: Baseline JIT (CodegenLIR), defect, P3)

Description

[William Maddox]

While analyzing an unrelated problem, I observed the following code generated for an LEA, that is, "addr = addp vars, offset":

    immi168 = immi 72
    addi10 = addi vars, immi168/*72*/
00008ec77c   or %g0, 72, %l2
00008ec780   addcc %l7, %l2, %l7
00008ec784   or %g0, -56, %l2
00008ec788   add %fp, %l2, %o4

In Assembler::asm_arith, the LEA case is recognized, and treated specially:

        else if ((op == LIR_addi || op == LIR_addxovi) && lhs->isop(LIR_allocp) && rhs->isImmI()) {
            // add alloc+const, use lea
            Register rr = deprecated_prepResultReg(ins, allow);
            int d = findMemFor(lhs) + rhs->immI();
            ADD(FP, L2, rr);
            SET32(d, L2);
        }

This results in the generation of the final two instructions in the example above, i.e.:

00008ec784   or %g0, -56, %l2
00008ec788   add %fp, %l2, %o4

Instead of exiting after peeling off this special case, however, asm_arith continues, emitting code for the general case of addi, resulting in two
additional instructions:

00008ec77c   or %g0, 72, %l2
00008ec780   addcc %l7, %l2, %l7

Recall that the assembler emits instructions in the reverse order form that in which they will be executed.

Comment 1

[William Maddox]

Attachment: Exit asm_arith after completing code generation for LEA idiom

Comment 2

[William Maddox]

Pushed to nanojit-central:

http://hg.mozilla.org/projects/nanojit-central/rev/639cf2aa6573

Comment 3

[Nicholas Nethercote [inactive]]

http://hg.mozilla.org/tracemonkey/rev/cc645910e1fa

Comment 4

[Robert Sayre]

http://hg.mozilla.org/mozilla-central/rev/cc645910e1fa

Comment 5

[Edwin Smith]

TR: http://hg.mozilla.org/tamarin-redux/rev/bb18dcbaeb68