[PATCH] D28527: Check for register clobbers when merging a vreg live range with a reserved physreg in RegisterCoalescer.

[Quentin Colombet via Phabricator via llvm-commits]

qcolombet added a comment.

> The "no-def+!allocatable => constant" rule has been there for a long time in MachineRegisterInfo::isConstantPhysReg()

Oh, I missed the !allocatable in the description of the problem.
Yeah, no need to investigate then.



================
Comment at: llvm/trunk/test/CodeGen/AArch64/regcoal-physreg.mir:78
+    ; Need a def of x18 so that it's not deduced as "constant".
+    %x18 = COPY %xzr
+    %7 = COPY %x18
----------------
You could use something else than x18 to avoid the !allocatable case that Matthias mentioned, right?
What I am saying is that the comment is a bit misleading as it is, because this is expected when register are not allocatable.


Repository:
  rL LLVM

https://reviews.llvm.org/D28527