This was discovered to be necessary while running memchr-01.ll with
-verify-machinstrs, because it is not allowed to have a phys reg live
accross block boundaries while on SSA form, if the register is
allocatable (expect in entry block and landing pads).
In this test case, stringRRE pseudos are expanded after isel by adding
a loop block which produces a live out CC register. To make the test
pass, it was also necessary to not say that StringRRELoop pseudo uses
R0L, this is only true for the StringRRE opcode.
-verify-machineinstrs added to memchr-01.ll test.
New test case int-cmp-51.ll to test that MachineCSE can eliminate
an identical compare (which it couldn't do before).
Reviewed by Ulrich Weigand
llvm-svn: 251634
SystemZTargetLowering::emitStringWrapper() previously loaded the character
into R0 before the loop and made R0 live on entry. I'd forgotten that
allocatable registers weren't allowed to be live across blocks at this stage,
and it confused LiveVariables enough to cause a miscompilation of f3 in
memchr-02.ll.
This patch instead loads R0 in the loop and leaves LICM to hoist it
after RA. This is actually what I'd tried originally, but I went for
the manual optimisation after noticing that R0 often wasn't being hoisted.
This bug forced me to go back and look at why, now fixed as r188774.
We should also try to optimize null checks so that they test the CC result
of the SRST directly. The select between null and the SRST GPR result could
then usually be deleted as dead.
llvm-svn: 188779
