[llvm] [X86] combineEXTRACT_SUBVECTOR - remove unnecessary bitcast handling. (PR #145496)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon created https://github.com/llvm/llvm-project/pull/145496

We already aggressively fold extract_subvector(bitcast()) -> bitcast(extract_subvector())

>From cb5c810407a005bb7cf06e292f54f4647398216e Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Tue, 24 Jun 2025 11:30:52 +0100
Subject: [PATCH] [X86] combineEXTRACT_SUBVECTOR - remove unnecessary bitcast
 handling.

We already aggressively fold extract_subvector(bitcast()) -> bitcast(extract_subvector())
---
 llvm/lib/Target/X86/X86ISelLowering.cpp | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index d5837ab938d4e..7c26dd6e2dc2f 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -59577,7 +59577,6 @@ static SDValue combineEXTRACT_SUBVECTOR(SDNode *N, SelectionDAG &DAG,
   MVT VT = N->getSimpleValueType(0);
   SDValue InVec = N->getOperand(0);
   unsigned IdxVal = N->getConstantOperandVal(1);
-  SDValue InVecBC = peekThroughBitcasts(InVec);
   EVT InVecVT = InVec.getValueType();
   unsigned SizeInBits = VT.getSizeInBits();
   unsigned InSizeInBits = InVecVT.getSizeInBits();
@@ -59594,7 +59593,7 @@ static SDValue combineEXTRACT_SUBVECTOR(SDNode *N, SelectionDAG &DAG,
   // This pattern emerges during AVX1 legalization. We handle it before lowering
   // to avoid complications like splitting constant vector loads.
   if (Subtarget.hasAVX() && !Subtarget.hasAVX2() && TLI.isTypeLegal(InVecVT) &&
-      InSizeInBits == 256 && InVecBC.getOpcode() == ISD::AND) {
+      InSizeInBits == 256 && InVec.getOpcode() == ISD::AND) {
     auto isConcatenatedNot = [](SDValue V) {
       V = peekThroughBitcasts(V);
       if (!isBitwiseNot(V))
@@ -59602,12 +59601,12 @@ static SDValue combineEXTRACT_SUBVECTOR(SDNode *N, SelectionDAG &DAG,
       SDValue NotOp = V->getOperand(0);
       return peekThroughBitcasts(NotOp).getOpcode() == ISD::CONCAT_VECTORS;
     };
-    if (isConcatenatedNot(InVecBC.getOperand(0)) ||
-        isConcatenatedNot(InVecBC.getOperand(1))) {
+    if (isConcatenatedNot(InVec.getOperand(0)) ||
+        isConcatenatedNot(InVec.getOperand(1))) {
       // extract (and v4i64 X, (not (concat Y1, Y2))), n -> andnp v2i64 X(n), Y1
-      SDValue Concat = splitVectorIntBinary(InVecBC, DAG, SDLoc(InVecBC));
       return DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, VT,
-                         DAG.getBitcast(InVecVT, Concat), N->getOperand(1));
+                         splitVectorIntBinary(InVec, DAG, DL),
+                         N->getOperand(1));
     }
   }
 
@@ -59691,7 +59690,7 @@ static SDValue combineEXTRACT_SUBVECTOR(SDNode *N, SelectionDAG &DAG,
     SmallVector<SDValue, 2> ShuffleInputs;
     unsigned NumSubVecs = InSizeInBits / SizeInBits;
     // Decode the shuffle mask and scale it so its shuffling subvectors.
-    if (getTargetShuffleInputs(InVecBC, ShuffleInputs, ShuffleMask, DAG) &&
+    if (getTargetShuffleInputs(InVec, ShuffleInputs, ShuffleMask, DAG) &&
         scaleShuffleElements(ShuffleMask, NumSubVecs, ScaledMask)) {
       unsigned SubVecIdx = IdxVal / NumSubElts;
       if (ScaledMask[SubVecIdx] == SM_SentinelUndef)