[SLP]Fix PR98838: do no replace condition of select-based logical op by poison.

If the reduction operation is a select-based logical op, the condition
should be replaced by the poison, better to replace by the non-poisoning
constant to prevent poison propagation in the vector code.

Fixes #98838

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -14201,9 +14201,23 @@ Value *BoUpSLP::vectorizeTree(
     for (Instruction *I : RemovedInsts) {
       if (getTreeEntry(I)->Idx != 0)
         continue;
+      SmallVector<SelectInst *> LogicalOpSelects;
       I->replaceUsesWithIf(PoisonValue::get(I->getType()), [&](Use &U) {
+        // Do not replace condition of the logical op in form select <cond>.
+        bool IsPoisoningLogicalOp = isa<SelectInst>(U.getUser()) &&
+                                    (match(U.getUser(), m_LogicalAnd()) ||
+                                     match(U.getUser(), m_LogicalOr())) &&
+                                    U.getOperandNo() == 0;
+        if (IsPoisoningLogicalOp) {
+          LogicalOpSelects.push_back(cast<SelectInst>(U.getUser()));
+          return false;
+        }
         return UserIgnoreList->contains(U.getUser());
       });
+      // Replace conditions of the poisoning logical ops with the non-poison
+      // constant value.
+      for (SelectInst *SI : LogicalOpSelects)
+        SI->setCondition(Constant::getNullValue(SI->getCondition()->getType()));
     }
   }
   // Retain to-be-deleted instructions for some debug-info bookkeeping and alias

llvm/test/Transforms/SLPVectorizer/X86/select-reduction-op.ll

@@ -0,0 +1,26 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S --passes=slp-vectorizer -mtriple=x86_64-unknown-linux < %s | FileCheck %s
+
+define i1 @src(i1 %cmp4.118.i) {
+; CHECK-LABEL: define i1 @src(
+; CHECK-SAME: i1 [[CMP4_118_I:%.*]]) {
+; CHECK-NEXT:    [[CMP4_118_I_NOT:%.*]] = xor i1 [[CMP4_118_I]], true
+; CHECK-NEXT:    [[TMP1:%.*]] = freeze <4 x i1> poison
+; CHECK-NEXT:    [[TMP2:%.*]] = call i1 @llvm.vector.reduce.or.v4i1(<4 x i1> [[TMP1]])
+; CHECK-NEXT:    [[OP_RDX:%.*]] = select i1 [[CMP4_118_I_NOT]], i1 true, i1 [[TMP2]]
+; CHECK-NEXT:    [[TMP3:%.*]] = freeze i1 [[OP_RDX]]
+; CHECK-NEXT:    [[OP_RDX1:%.*]] = select i1 [[TMP3]], i1 true, i1 poison
+; CHECK-NEXT:    ret i1 [[OP_RDX1]]
+;
+  %cmp4.118.i.not = xor i1 %cmp4.118.i, true
+  %brmerge = select i1 %cmp4.118.i.not, i1 true, i1 poison
+  %.not = xor i1 poison, true
+  %brmerge2 = select i1 %brmerge, i1 true, i1 %.not
+  %.not3 = xor i1 poison, true
+  %brmerge4 = select i1 %brmerge2, i1 true, i1 %.not3
+  %.not5 = xor i1 poison, true
+  %brmerge6 = select i1 %brmerge4, i1 true, i1 %.not5
+  %.not7 = xor i1 poison, true
+  %brmerge8 = select i1 %brmerge6, i1 true, i1 %.not7
+  ret i1 %brmerge8
+}