[llvm-branch-commits] [llvm] release/23.x: [SelectionDAG] Avoid irregular INSERT_SUBVECTOR when widening CTTZ_ELTS (#218019) (PR #219444)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-selectiondag

Author: llvmbot

<details>
<summary>Changes</summary>

Backport 01ff7258c2374b3cca02bc8631a445ac32f9b930

Requested by: @<!-- -->RKSimon

---
Full diff: https://github.com/llvm/llvm-project/pull/219444.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp (+14-3) 
- (modified) llvm/test/CodeGen/X86/intrinsic-cttz-elts.ll (+67) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
index 3817a77f8bd44..c0fab69cb518a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
@@ -8738,8 +8738,8 @@ SDValue DAGTypeLegalizer::WidenVecOp_VSELECT(SDNode *N) {
 SDValue DAGTypeLegalizer::WidenVecOp_CttzElements(SDNode *N) {
   SDLoc DL(N);
   SDValue Source = N->getOperand(0);
-  EVT WideVT =
-      TLI.getTypeToTransformTo(*DAG.getContext(), Source.getValueType());
+  EVT SourceVT = Source.getValueType();
+  EVT WideVT = TLI.getTypeToTransformTo(*DAG.getContext(), SourceVT);
 
   SDValue WideSource;
   if (N->getOpcode() == ISD::CTTZ_ELTS_ZERO_POISON) {
@@ -8748,7 +8748,18 @@ SDValue DAGTypeLegalizer::WidenVecOp_CttzElements(SDNode *N) {
     // Pad the widened portion with all-ones so the extra lanes appear as
     // active (non-zero) elements and do not contribute trailing zeros.
     SDValue AllOnes = DAG.getAllOnesConstant(DL, WideVT);
-    WideSource = DAG.getInsertSubvector(DL, AllOnes, Source, 0);
+    if (WideVT.isFixedLengthVector() &&
+        getTypeAction(WideVT) == TargetLowering::TypeSplitVector) {
+      WideSource = GetWidenedVector(Source);
+      unsigned WideElts = WideVT.getVectorNumElements();
+      SmallVector<int> Mask(WideElts);
+      std::iota(Mask.begin(), Mask.end(), 0);
+      for (unsigned I = SourceVT.getVectorNumElements(); I != WideElts; ++I)
+        Mask[I] += WideElts;
+      WideSource = DAG.getVectorShuffle(WideVT, DL, WideSource, AllOnes, Mask);
+    } else {
+      WideSource = DAG.getInsertSubvector(DL, AllOnes, Source, 0);
+    }
   }
 
   return DAG.getNode(N->getOpcode(), DL, N->getValueType(0), WideSource,
diff --git a/llvm/test/CodeGen/X86/intrinsic-cttz-elts.ll b/llvm/test/CodeGen/X86/intrinsic-cttz-elts.ll
index f8cc45c1b5bda..a2f2ffdfd3325 100644
--- a/llvm/test/CodeGen/X86/intrinsic-cttz-elts.ll
+++ b/llvm/test/CodeGen/X86/intrinsic-cttz-elts.ll
@@ -196,5 +196,72 @@ define i32 @ctz_zero_v8i1() {
   ret i32 %res
 }
 
+; Irregular predicate vectors widen to a power-of-two number of lanes. The
+; widened lanes must be active so an all-zero input returns the original lane
+; count, without requiring an irregular INSERT_SUBVECTOR during legalization.
+define i32 @ctz_zero_v17i1() {
+; CHECK-LABEL: ctz_zero_v17i1:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movdqa {{.*#+}} xmm0 = [84281096,16909060,84281096,16909060]
+; CHECK-NEXT:    pmaxub {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0
+; CHECK-NEXT:    pshufd {{.*#+}} xmm1 = xmm0[1,1,1,1]
+; CHECK-NEXT:    pmaxub %xmm0, %xmm1
+; CHECK-NEXT:    movdqa %xmm1, %xmm0
+; CHECK-NEXT:    psrld $16, %xmm0
+; CHECK-NEXT:    pmaxub %xmm1, %xmm0
+; CHECK-NEXT:    movdqa %xmm0, %xmm1
+; CHECK-NEXT:    psrlw $8, %xmm1
+; CHECK-NEXT:    pmaxub %xmm0, %xmm1
+; CHECK-NEXT:    movd %xmm1, %eax
+; CHECK-NEXT:    movb $16, %cl
+; CHECK-NEXT:    subb %al, %cl
+; CHECK-NEXT:    movzbl %cl, %eax
+; CHECK-NEXT:    addl $16, %eax
+; CHECK-NEXT:    retq
+;
+; AVX512-LABEL: ctz_zero_v17i1:
+; AVX512:       # %bb.0:
+; AVX512-NEXT:    vpmovzxbw {{.*#+}} xmm0 = [240,242,244,246,248,250,252,254]
+; AVX512-NEXT:    vpminub {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0, %xmm0
+; AVX512-NEXT:    vphminposuw %xmm0, %xmm0
+; AVX512-NEXT:    vmovd %xmm0, %eax
+; AVX512-NEXT:    addb $17, %al
+; AVX512-NEXT:    movzbl %al, %eax
+; AVX512-NEXT:    addl $16, %eax
+; AVX512-NEXT:    retq
+  %res = call i32 @llvm.experimental.cttz.elts.i32.v17i1(<17 x i1> zeroinitializer, i1 false)
+  ret i32 %res
+}
+
+define i32 @ctz_zero_v31i1() {
+; CHECK-LABEL: ctz_zero_v31i1:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movdqa {{.*#+}} xmm0 = [16777216,16777216,16777216,16777216]
+; CHECK-NEXT:    pmaxub {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0
+; CHECK-NEXT:    movdqa %xmm0, %xmm1
+; CHECK-NEXT:    psrld $24, %xmm1
+; CHECK-NEXT:    psrld $16, %xmm0
+; CHECK-NEXT:    pmaxub %xmm1, %xmm0
+; CHECK-NEXT:    movd %xmm0, %eax
+; CHECK-NEXT:    movb $16, %cl
+; CHECK-NEXT:    subb %al, %cl
+; CHECK-NEXT:    movzbl %cl, %eax
+; CHECK-NEXT:    addl $16, %eax
+; CHECK-NEXT:    retq
+;
+; AVX512-LABEL: ctz_zero_v31i1:
+; AVX512:       # %bb.0:
+; AVX512-NEXT:    vpmovzxbw {{.*#+}} xmm0 = [255,255,255,255,255,255,255,254]
+; AVX512-NEXT:    vpminub {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0, %xmm0
+; AVX512-NEXT:    vphminposuw %xmm0, %xmm0
+; AVX512-NEXT:    vmovd %xmm0, %eax
+; AVX512-NEXT:    addb $17, %al
+; AVX512-NEXT:    movzbl %al, %eax
+; AVX512-NEXT:    addl $16, %eax
+; AVX512-NEXT:    retq
+  %res = call i32 @llvm.experimental.cttz.elts.i32.v31i1(<31 x i1> zeroinitializer, i1 false)
+  ret i32 %res
+}
+
 declare i8 @llvm.experimental.cttz.elts.i8.v8i16(<8 x i16>, i1)
 declare i16 @llvm.experimental.cttz.elts.i16.v4i32(<4 x i32>, i1)

``````````

</details>


https://github.com/llvm/llvm-project/pull/219444