[SLP]Fix PR52090: clang crashes: Assertion `Index < Length && "Invalid index!"' failed.

Need to check that either Idx is UndefMaskElem and value is UndefValue
or Idx is valid and value is the same as the scalar value in the node.

Differential Revision: https://reviews.llvm.org/D111802

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -1640,9 +1640,12 @@ class BoUpSLP {
         if (Mask.size() != VL.size() && VL.size() == Scalars.size())
           return std::equal(VL.begin(), VL.end(), Scalars.begin());
         return VL.size() == Mask.size() &&
-               std::equal(
-                   VL.begin(), VL.end(), Mask.begin(),
-                   [Scalars](Value *V, int Idx) { return V == Scalars[Idx]; });
+               std::equal(VL.begin(), VL.end(), Mask.begin(),
+                          [Scalars](Value *V, int Idx) {
+                            return (isa<UndefValue>(V) &&
+                                    Idx == UndefMaskElem) ||
+                                   (Idx != UndefMaskElem && V == Scalars[Idx]);
+                          });
       };
       if (!ReorderIndices.empty()) {
         // TODO: implement matching if the nodes are just reordered, still can

llvm/test/Transforms/SLPVectorizer/X86/crash_undef_mask_elem.ll

@@ -0,0 +1,47 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -slp-vectorizer -S -o - -mtriple=x86_64 < %s | FileCheck %s
+
+define void @main(i32 %x, i1 %b) {
+; CHECK-LABEL: @main(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[B:%.*]], label [[L3:%.*]], label [[L1_THREAD:%.*]]
+; CHECK:       L1:
+; CHECK-NEXT:    br label [[L3]]
+; CHECK:       L1.thread:
+; CHECK-NEXT:    br label [[L3]]
+; CHECK:       L3:
+; CHECK-NEXT:    [[DOTPR21:%.*]] = phi i32 [ [[X:%.*]], [[ENTRY:%.*]] ], [ [[DOTPR21]], [[L1:%.*]] ], [ [[X]], [[L1_THREAD]] ]
+; CHECK-NEXT:    [[DOTOLD_PR15:%.*]] = phi i32 [ [[X]], [[ENTRY]] ], [ 0, [[L1]] ], [ [[X]], [[L1_THREAD]] ]
+; CHECK-NEXT:    [[H_1:%.*]] = phi i32 [ undef, [[ENTRY]] ], [ undef, [[L1]] ], [ undef, [[L1_THREAD]] ]
+; CHECK-NEXT:    [[I_2:%.*]] = phi i32 [ 1, [[ENTRY]] ], [ [[I_2]], [[L1]] ], [ 1, [[L1_THREAD]] ]
+; CHECK-NEXT:    [[K_3:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ [[I_2]], [[L1]] ], [ 1, [[L1_THREAD]] ]
+; CHECK-NEXT:    [[G_1:%.*]] = phi i32 [ undef, [[ENTRY]] ], [ [[O_1:%.*]], [[L1]] ], [ undef, [[L1_THREAD]] ]
+; CHECK-NEXT:    [[M_3:%.*]] = phi i32 [ undef, [[ENTRY]] ], [ [[I_2]], [[L1]] ], [ 1, [[L1_THREAD]] ]
+; CHECK-NEXT:    [[O_1]] = phi i32 [ undef, [[ENTRY]] ], [ [[O_1]], [[L1]] ], [ undef, [[L1_THREAD]] ]
+; CHECK-NEXT:    br label [[L4:%.*]]
+; CHECK:       L4:
+; CHECK-NEXT:    br label [[L1]]
+;
+entry:
+  br i1 %b, label %L3, label %L1.thread
+
+L1:
+  br label %L3
+
+L1.thread:
+  br label %L3
+
+L3:
+  %.pr21 = phi i32 [ %x, %entry ], [ %.pr21, %L1 ], [ %x, %L1.thread ]
+  %.old.pr15 = phi i32 [ %x, %entry ], [ 0, %L1 ], [ %x, %L1.thread ]
+  %h.1 = phi i32 [ undef, %entry ], [ undef, %L1 ], [ undef, %L1.thread ]
+  %i.2 = phi i32 [ 1, %entry ], [ %i.2, %L1 ], [ 1, %L1.thread ]
+  %k.3 = phi i32 [ 0, %entry ], [ %i.2, %L1 ], [ 1, %L1.thread ]
+  %g.1 = phi i32 [ undef, %entry ], [ %o.1, %L1 ], [ undef, %L1.thread ]
+  %m.3 = phi i32 [ undef, %entry ], [ %i.2, %L1 ], [ 1, %L1.thread ]
+  %o.1 = phi i32 [ undef, %entry ], [ %o.1, %L1 ], [ undef, %L1.thread ]
+  br label %L4
+
+L4:
+  br label %L1
+}