[llvm] [AMDGPU] Add commute for some VOP3 inst (PR #121326)

[Matt Arsenault via llvm-commits]

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@@ -2798,7 +2798,8 @@ MachineInstr *SIInstrInfo::commuteInstructionImpl(MachineInstr &MI, bool NewMI,
   } else if (!Src0.isReg() && Src1.isReg()) {
     if (isOperandLegal(MI, Src1Idx, &Src0))
       CommutedMI = swapRegAndNonRegOperand(MI, Src1, Src0);
-  } else if (isInlineConstant(Src0) && isInlineConstant(Src1)) {
+  } else if (isInlineConstant(Src1)) {
+    // If Src1 is inline constant and Src0 is not, then isOperandLegal rejects
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arsenm wrote:

This isn't explaining why to do this, but this is also an API flaw that's always been there. We need an isOperandLegal that doesn't account for the context of the other operands 

https://github.com/llvm/llvm-project/pull/121326