RFR: 8279225: C1 longs comparison operation destroys argument registers

[Hao Sun]

On Fri, 24 Dec 2021 16:25:37 GMT, Sergey Nazarkin <snazarki at openjdk.org> wrote:

> Several regression tests are failed on arm32 CPU if tiered compilation is enabled.
> 
> The list includes
> java/math/BigDecimal/DivideMcTests
> java/util/Arrays/Sorting.java
> java/util/Arrays/SortingNearlySortedPrimitive.java
> java/util/concurrent/tck/JSR166TestCase
> java/util/stream/SliceOpTest.java
> etc
> 
> It appears C1 comp_op for long operands destroys arguments registers:
> void LIR_Assembler::comp_op(LIR_Condition condition, LIR_Opr opr1, LIR_Opr opr2, LIR_Op2* op) {
> ....
>       Register ylo = opr2->as_register_lo();
>       Register yhi = opr2->as_register_hi();
>       if (condition == lir_cond_equal || condition == lir_cond_notEqual) {
>         __ teq(xhi, yhi);
>         __ teq(xlo, ylo, eq);
>       } else {
>         __ subs(xlo, xlo, ylo); // <<< incorrect
>         __ sbcs(xhi, xhi, yhi); // <<< incorrect
>       }
> ...
> } 
> 
> Tested with hotspot_tier2, jdk_tier3 on linux_arm

This fix looks good to me. (I'm not a Reviewer).

One thing to remind is that the PR and JBS should use the same title.

src/hotspot/cpu/arm/c1_LIRAssembler_arm.cpp line 1823:

> 1821:         __ teq(xlo, ylo, eq);
> 1822:       } else {
> 1823:         __ cmp(xlo, ylo);

nit: we may want to use `__ subs(Rtemp, xlo, ylo);` here to align with the usage in match rules in arm.ad, e.g., `compL_reg_reg_LEGT`. It's okay to me if you use `cmp` anyway.

-------------

Marked as reviewed by haosun (Author).

PR: https://git.openjdk.java.net/jdk/pull/6934