[llvm] [AMDGPU] siloadstoreopt generate REG_SEQUENCE with aligned operands (PR #162088)

[Janek van Oirschot via llvm-commits]

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@@ -1411,12 +1420,24 @@ SILoadStoreOptimizer::copyFromSrcRegs(CombineInfo &CI, CombineInfo &Paired,
   const auto *Src0 = TII->getNamedOperand(*CI.I, OpName);
   const auto *Src1 = TII->getNamedOperand(*Paired.I, OpName);
 
-  BuildMI(*MBB, InsertBefore, DL, TII->get(AMDGPU::REG_SEQUENCE), SrcReg)
-      .add(*Src0)
-      .addImm(SubRegIdx0)
-      .add(*Src1)
-      .addImm(SubRegIdx1);
-
+  // Make sure the generated REG_SEQUENCE has sensibly aligned registers.
+  if (isCompatibleAlignSubReg(Paired.DataRC, SubRegIdx1, STM, TRI)) {
+    BuildMI(*MBB, InsertBefore, DL, TII->get(AMDGPU::REG_SEQUENCE), SrcReg)
+        .add(*Src0)
+        .addImm(SubRegIdx0)
+        .add(*Src1)
+        .addImm(SubRegIdx1);
+  } else {
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JanekvO wrote:

Played around with `getSubClassWithSubReg` but not quite sure how to use that in this context: a lot of times it'd return the same RC as put in. However, did help me find `getSubRegisterClass`.

https://github.com/llvm/llvm-project/pull/162088