[PATCH] D75421: [AArch64][GlobalISel] Avoid copies to target register bank for subregister copies

[Jessica Paquette via Phabricator via llvm-commits]

paquette added inline comments.


================
Comment at: llvm/test/CodeGen/AArch64/GlobalISel/subreg-copy.mir:37
+  bb.0:
+    %1:gpr(p0) = G_GLOBAL_VALUE @a
+    %3:gpr(s64) = G_CONSTANT i64 1
----------------
Do you have to use `G_GLOBAL_VALUE` here? Would this work instead?

```
bb.0:
liveins: $x0
  %1:gpr(p0) = COPY $x0
```

Then you could replace the `G_LOAD` with

```
%0:fpr(s128) = G_LOAD %1:gpr(p0) :: (load 16)
```

If you can do that, then you can delete the entire IR section in the testcase.

(You might have to add `tracksRegLiveness: true` to make this work)


================
Comment at: llvm/test/CodeGen/AArch64/GlobalISel/subreg-copy.mir:43-49
+    %4:gpr(s64) = G_AND %8:gpr, %3:gpr
+    %7:gpr(s32) = G_ICMP intpred(ne), %4:gpr(s64), %5:gpr
+    %6:gpr(s1) = G_TRUNC %7:gpr(s32)
+    G_BRCOND %6:gpr(s1), %bb.1
+
+  bb.1:
+    RET_ReallyLR
----------------
Is anything after the `COPY` necessary to test the behaviour here? Can we just return the result of the COPY? E.g.

```
$x1 = COPY %8:gpr(s64)
RET_ReallyLR implicit $x1
```


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  https://reviews.llvm.org/D75421/new/

https://reviews.llvm.org/D75421