[DAGCombiner] combine vextract (v1iX extract_subvector(vNiX, Idx)) into vextract(vNiX,Idx).

[eladcohen]

Summary

Combine vextract (v1iX extract_subvector(vNiX, Idx)) into vextract(vNiX,Idx).
This case appeared in AVX512 after fixing pr33349 in r310552.

Usually we don't get these cases since v1iX are illegal in most targets and then these
(v1iX extract_subvector(vNiX, Idx)) get scalarized into (iX vextract(vNiX,Idx)).
But for targets like AVX512 where such type is legal we end up with a redundant DAG
node which can be combined.

[RKSimon]

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

13790 ↗

(On Diff #110529)

Would this be better in SelectionDAG::getNode() ?

[eladcohen]

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

13790 ↗

(On Diff #110529)

Sounds good. I'll move it.

[eladcohen]

Fixed Simon's comments.

[RKSimon]

LGTM with a couple of minors

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

4378

vector

4381

Move this up to the rest of the comment

[eladcohen]

Fixed Simon's comments. Thanks for the review!

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

if (N1.getOpcode() == ISD::INSERT_VECTOR_ELT) {
             return N1.getOperand(1);
           else
             return getSExtOrTrunc(N1.getOperand(1), DL, VT);
         }
 
         return getNode(ISD::EXTRACT_VECTOR_ELT, DL, VT, N1.getOperand(0), N2);
       }
     }
+
+    // EXTRACT_VECTOR_ELT of v1iX EXTRACT_SUBVECTOR could be formed
+    // when vetor types are scalarized and v1iX is legal.
+    if (N1.getOpcode() == ISD::EXTRACT_SUBVECTOR &&
+        N1.getValueType().getVectorNumElements() == 1) {
+      // vextract (v1iX extract_subvector(vNiX, Idx)) -> vextract(vNiX,Idx)
+      return getNode(ISD::EXTRACT_VECTOR_ELT, DL, VT, N1.getOperand(0),
+                     N1.getOperand(1));
+    }
     break;
   case ISD::EXTRACT_ELEMENT:
     assert(N2C && (unsigned)N2C->getZExtValue() < 2 && "Bad EXTRACT_ELEMENT!");
     assert(!N1.getValueType().isVector() && !VT.isVector() &&
            (N1.getValueType().isInteger() == VT.isInteger()) &&
            N1.getValueType() != VT &&
            "Wrong types for EXTRACT_ELEMENT!");
 

test/CodeGen/X86/pr33349.ll

 ;
 ; SKX-LABEL: test:
 ; SKX:       # BB#0: # %bb
 ; SKX-NEXT:    vpslld $31, %xmm0, %xmm0
 ; SKX-NEXT:    vptestmd %xmm0, %xmm0, %k0
 ; SKX-NEXT:    kshiftrw $2, %k0, %k1
 ; SKX-NEXT:    kshiftlw $15, %k1, %k2
 ; SKX-NEXT:    kshiftrw $15, %k2, %k2
-; SKX-NEXT:    kshiftlw $15, %k2, %k2
-; SKX-NEXT:    kshiftrw $15, %k2, %k2
 ; SKX-NEXT:    kmovd %k2, %eax
 ; SKX-NEXT:    testb $1, %al
 ; SKX-NEXT:    fld1
 ; SKX-NEXT:    fldz
 ; SKX-NEXT:    fld %st(0)
 ; SKX-NEXT:    fcmovne %st(2), %st(0)
 ; SKX-NEXT:    kshiftlw $14, %k1, %k1
 ; SKX-NEXT:    kshiftrw $15, %k1, %k1
-; SKX-NEXT:    kshiftlw $15, %k1, %k1
-; SKX-NEXT:    kshiftrw $15, %k1, %k1
 ; SKX-NEXT:    kmovd %k1, %eax
 ; SKX-NEXT:    testb $1, %al
 ; SKX-NEXT:    fld %st(1)
 ; SKX-NEXT:    fcmovne %st(3), %st(0)
 ; SKX-NEXT:    kshiftlw $15, %k0, %k1
 ; SKX-NEXT:    kshiftrw $15, %k1, %k1
-; SKX-NEXT:    kshiftlw $15, %k1, %k1
-; SKX-NEXT:    kshiftrw $15, %k1, %k1
 ; SKX-NEXT:    kmovd %k1, %eax
 ; SKX-NEXT:    testb $1, %al
 ; SKX-NEXT:    fld %st(2)
 ; SKX-NEXT:    fcmovne %st(4), %st(0)
 ; SKX-NEXT:    kshiftlw $14, %k0, %k0
 ; SKX-NEXT:    kshiftrw $15, %k0, %k0
-; SKX-NEXT:    kshiftlw $15, %k0, %k0
-; SKX-NEXT:    kshiftrw $15, %k0, %k0
 ; SKX-NEXT:    kmovd %k0, %eax
 ; SKX-NEXT:    testb $1, %al
 ; SKX-NEXT:    fxch %st(3)
 ; SKX-NEXT:    fcmovne %st(4), %st(0)
 ; SKX-NEXT:    fstp %st(4)
 ; SKX-NEXT:    fxch %st(3)
 ; SKX-NEXT:    fstpt 10(%rdi)
 ; SKX-NEXT:    fxch %st(1)