[IR] Make hasPoisonGeneratingMetadata return false if has !noundef

[StephenFan]

Summary

hasPoisonGeneratingMetadata is used by ValueTracking function
canCreateUndefOrPoison, if both poison generating metadata and
!noundef exists, then this instruction can not create undef or poison
actually.

But I am not sure if it is correct since !noundef can be dropped. If we
first do the transform based on !noundef, then we drop it in other
transforms, does it still correct?

llvm/lib/IR/Instruction.cpp

if (isa<FPMathOperator>(this)) {
     setHasNoNaNs(false);
     setHasNoInfs(false);
   }
 
   assert(!hasPoisonGeneratingFlags() && "must be kept in sync");
 }
 
 bool Instruction::hasPoisonGeneratingMetadata() const {
-  return hasMetadata(LLVMContext::MD_range) ||
+  return (hasMetadata(LLVMContext::MD_range) ||
           hasMetadata(LLVMContext::MD_nonnull) ||
-         hasMetadata(LLVMContext::MD_align);
+          hasMetadata(LLVMContext::MD_align)) &&
+         !hasMetadata(LLVMContext::MD_noundef);
 }
 
 void Instruction::dropPoisonGeneratingMetadata() {
   eraseMetadata(LLVMContext::MD_range);
   eraseMetadata(LLVMContext::MD_nonnull);
   eraseMetadata(LLVMContext::MD_align);
 }
 

llvm/test/Transforms/InstCombine/select-and-or.ll

 ; CHECK-NEXT:    ret <2 x i1> [[R]]
 ;
   %c = call <2 x i1> @gen_v2i1()
   %nota = xor <2 x i1> %a, <i1 true, i1 true>
   %cond = or <2 x i1> %c, %nota
   %r = select <2 x i1> %cond, <2 x i1> %a, <2 x i1> %b
   ret <2 x i1> %r
 }
+
+define i1 @poison_metadata(i32 noundef %a, i1 %b) {
+; CHECK-LABEL: @poison_metadata(
+; CHECK-NEXT:    [[C:%.*]] = call i32 @llvm.ctpop.i32(i32 [[A:%.*]]), !range [[RNG0:![0-9]+]], !noundef !1
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[C]], 3
+; CHECK-NEXT:    [[R:%.*]] = and i1 [[CMP]], [[B:%.*]]
+; CHECK-NEXT:    ret i1 [[R]]
+;
+  %c = call i32 @llvm.ctpop.i32(i32 %a), !range !0, !noundef !1
+  %cmp = icmp ugt i32 %c, 2
+  %r = select i1 %b, i1 %cmp, i1 false
+  ret i1 %r
+}
+
+!0 = !{i32 0, i32 4}
+!1 = !{}
+declare i32 @llvm.ctpop.i32(i32)