[llvm] [AMDGPU] Don't fold an i64 immediate value if it can't be replicated from its lower 32-bit (PR #168458)

[Shilei Tian via llvm-commits]

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@@ -766,6 +771,34 @@ static void appendFoldCandidate(SmallVectorImpl<FoldCandidate> &FoldList,
                       FoldCandidate(MI, OpNo, FoldOp, Commuted, ShrinkOp));
 }
 
+// Returns true if the instruction is a packed f32 instruction that only reads
+// 32 bits from a scalar operand (SGPR or literal) and replicates the bits to
+// both channels.
+static bool isPKF32Instr(const GCNSubtarget *ST, MachineInstr *MI) {
+  if (!ST->hasPKF32Insts())
+    return false;
+  switch (MI->getOpcode()) {
+  case AMDGPU::V_PK_ADD_F32:
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shiltian wrote:

but then we need to get `MCInstrDesc`, and then `MCOperandInfo`, but eventually what's the point?

https://github.com/llvm/llvm-project/pull/168458