[PATCH] D71386: [AMDGPU] Remove unnecessary v_mov from a register to itself in WQM lowering.

[Michael Bedy via Phabricator via llvm-commits]

mjbedy added inline comments.


================
Comment at: llvm/lib/Target/AMDGPU/SIWholeQuadMode.cpp:877-878
+  for (MachineInstr *MI : LowerToCopyInstrs) {
+    for (unsigned i = MI->getNumExplicitOperands() - 1; i > 1; i--)
+      MI->RemoveOperand(i);
+
----------------
nhaehnle wrote:
> arsenm wrote:
> > These should only ever have been moves to begin with? Just remove the one exec operand?
> They were move-like: WQM, SOFT_WQM, V_SET_INACTIVE_xx. I think it makes sense though to just remove that one operand and maybe assert there are no other implicit uses.
Now that I look closer at this, I'm not even sure what this loop is doing (or the one in the case above that I modeled it on)? The exec operands are implicit so this doesn't touch them. This is what comes into the phase:

%12:vgpr_32 = WQM %10:vgpr_32, implicit $exec, implicit $exec

And this is what comes out:

%12:vgpr_32 = COPY %10:vgpr_32, implicit $exec, implicit $exec



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https://reviews.llvm.org/D71386