[X86] combineLoad - allow constant loads to share matching 'lower constant bits' with larger VBROADCAST_LOAD/SUBV_BROADCAST_LOAD nodes

We already had separate support for VBROADCAST_LOAD - merge this with the generic load handling and add SUBV_BROADCAST_LOAD support as well.

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -49963,33 +49963,15 @@ static SDValue combineLoad(SDNode *N, SelectionDAG &DAG,
           }
           return true;
         };
-        if (User->getOpcode() == X86ISD::VBROADCAST_LOAD &&
-            getTargetConstantFromBasePtr(Ptr)) {
-          // See if we are loading a constant that has also been broadcast.
-          APInt Undefs, UserUndefs;
-          SmallVector<APInt> Bits, UserBits;
-          if (getTargetConstantBitsFromNode(SDValue(N, 0), 8, Undefs, Bits) &&
-              getTargetConstantBitsFromNode(SDValue(User, 0), 8, UserUndefs,
-                                            UserBits)) {
-            UserUndefs = UserUndefs.trunc(Undefs.getBitWidth());
-            UserBits.truncate(Bits.size());
-            if (MatchingBits(Undefs, UserUndefs, Bits, UserBits)) {
-              SDValue Extract = extractSubVector(
-                  SDValue(User, 0), 0, DAG, SDLoc(N), RegVT.getSizeInBits());
-              Extract = DAG.getBitcast(RegVT, Extract);
-              return DCI.CombineTo(N, Extract, SDValue(User, 1));
-            }
-          }
-        }
-        if (ISD::isNormalLoad(User)) {
-          // See if we are loading a constant that matches in the lower
-          // bits of a longer constant (but from a different constant pool ptr).
-          SDValue UserPtr = cast<MemSDNode>(User)->getBasePtr();
-          const Constant *LdC = getTargetConstantFromBasePtr(Ptr);
-          const Constant *UserC = getTargetConstantFromBasePtr(UserPtr);
-          if (LdC && UserC && UserPtr != Ptr &&
-              LdC->getType()->getPrimitiveSizeInBits() <
-                  UserC->getType()->getPrimitiveSizeInBits()) {
+        // See if we are loading a constant that matches in the lower
+        // bits of a longer constant (but from a different constant pool ptr).
+        SDValue UserPtr = cast<MemSDNode>(User)->getBasePtr();
+        const Constant *LdC = getTargetConstantFromBasePtr(Ptr);
+        const Constant *UserC = getTargetConstantFromBasePtr(UserPtr);
+        if (LdC && UserC && UserPtr != Ptr) {
+          unsigned LdSize = LdC->getType()->getPrimitiveSizeInBits();
+          unsigned UserSize = UserC->getType()->getPrimitiveSizeInBits();
+          if (LdSize < UserSize || !ISD::isNormalLoad(User)) {
             APInt Undefs, UserUndefs;
             SmallVector<APInt> Bits, UserBits;
             if (getTargetConstantBitsFromNode(SDValue(N, 0), 8, Undefs, Bits) &&

llvm/test/CodeGen/X86/broadcast-elm-cross-splat-vec.ll

@@ -1459,17 +1459,16 @@ define <8 x i64> @f8xi64_i128(<8 x i64> %a) {
 ;
 ; AVX-64-LABEL: f8xi64_i128:
 ; AVX-64:       # %bb.0:
-; AVX-64-NEXT:    vextractf128 $1, %ymm1, %xmm2
-; AVX-64-NEXT:    vmovdqa {{.*#+}} xmm3 = [0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0]
-; AVX-64-NEXT:    vpaddq %xmm3, %xmm2, %xmm2
-; AVX-64-NEXT:    vpaddq %xmm3, %xmm1, %xmm1
-; AVX-64-NEXT:    vinsertf128 $1, %xmm2, %ymm1, %ymm1
-; AVX-64-NEXT:    vextractf128 $1, %ymm0, %xmm2
-; AVX-64-NEXT:    vpaddq %xmm3, %xmm2, %xmm2
-; AVX-64-NEXT:    vpaddq %xmm3, %xmm0, %xmm0
-; AVX-64-NEXT:    vinsertf128 $1, %xmm2, %ymm0, %ymm0
-; AVX-64-NEXT:    vbroadcastf128 {{.*#+}} ymm2 = [0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0]
+; AVX-64-NEXT:    vbroadcastf128 {{.*#+}} ymm2 = [0,1,0,1]
 ; AVX-64-NEXT:    # ymm2 = mem[0,1,0,1]
+; AVX-64-NEXT:    vextractf128 $1, %ymm1, %xmm3
+; AVX-64-NEXT:    vpaddq %xmm2, %xmm3, %xmm3
+; AVX-64-NEXT:    vpaddq %xmm2, %xmm1, %xmm1
+; AVX-64-NEXT:    vinsertf128 $1, %xmm3, %ymm1, %ymm1
+; AVX-64-NEXT:    vextractf128 $1, %ymm0, %xmm3
+; AVX-64-NEXT:    vpaddq %xmm2, %xmm3, %xmm3
+; AVX-64-NEXT:    vpaddq %xmm2, %xmm0, %xmm0
+; AVX-64-NEXT:    vinsertf128 $1, %xmm3, %ymm0, %ymm0
 ; AVX-64-NEXT:    vandps %ymm2, %ymm0, %ymm0
 ; AVX-64-NEXT:    vandps %ymm2, %ymm1, %ymm1
 ; AVX-64-NEXT:    retq