[llvm] [RISCV] Reorder insert_subvector and bitcast in getDeinterleaveShiftAndTrunc. (PR #127258)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-risc-v

Author: Craig Topper (topperc)

<details>
<summary>Changes</summary>

Put the bitcast before the insert_subvector. It's more likely the insert subvector can be combined with other nodes. The insert_subvector only needed sometimes, and I'm considering reusing this function which might require pulling the insert_subvector out.

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Full diff: https://github.com/llvm/llvm-project/pull/127258.diff


1 Files Affected:

- (modified) llvm/lib/Target/RISCV/RISCVISelLowering.cpp (+4-4) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index da04880348af6..9784ef13f3782 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -4660,10 +4660,10 @@ static SDValue getDeinterleaveShiftAndTrunc(const SDLoc &DL, MVT VT,
   SDValue Res = DAG.getNode(ISD::SRL, DL, WideSrcVT, Src,
                             DAG.getConstant(Shift, DL, WideSrcVT));
   Res = DAG.getNode(ISD::TRUNCATE, DL, ResVT, Res);
-  MVT IntVT = VT.changeVectorElementTypeToInteger();
-  Res = DAG.getNode(ISD::INSERT_SUBVECTOR, DL, IntVT, DAG.getUNDEF(IntVT), Res,
-                    DAG.getVectorIdxConstant(0, DL));
-  return DAG.getBitcast(VT, Res);
+  MVT CastVT = ResVT.changeVectorElementType(VT.getVectorElementType());
+  Res = DAG.getBitcast(CastVT, Res);
+  return DAG.getNode(ISD::INSERT_SUBVECTOR, DL, VT, DAG.getUNDEF(VT), Res,
+                     DAG.getVectorIdxConstant(0, DL));
 }
 
 // Lower the following shuffle to vslidedown.

``````````

</details>


https://github.com/llvm/llvm-project/pull/127258