[Bug target/104440] nvptx: FAIL: gcc.c-torture/execute/pr53465.c execution test

["vries at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104440

--- Comment #8 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 52456
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52456&action=edit
Tentative patch, introducing -minit-regs=<0|1|2>

This patch fixes the problem, and survived a standalone build and gcc testsuite
run.

Currently testing in offloading setting.

Uses DF_MIR_IN, otherwise only used by pass_ree.

Effect of -minit-regs=1 (insert init at function entry):
...
        .reg.pred %r50;
        .reg.pred %r51;
        .reg.u32 %r52;
+               mov.u32 %r26, 0;
                mov.u64 %r33, %ar0;
                mov.u32 %r34, %ar1;
                setp.le.s32     %r35, %r34, 0;
...

Effect of -minit-regs=2 (insert init close to use):
...
                add.u64 %r32, %r33, %r37;
                mov.u32 %r31, 0;
                mov.u32 %r52, 1;
+               mov.u32 %r26, 0;
 $L4:
                mov.u32 %r30, %r26;
                ld.u32  %r26, [%r25];
...