[ValueTracking] And & Or propagate poison.

[fhahn]

Summary

Both And and Or instructions propagate poison if any operand is poison.
Note the TODO in the function that most instructions expect a few should
propagate poison, but it is probably safer to enable them step-by-step.

[aqjune]

Hi,
There is a relevant ongoing patch : D78615
Would it make sense if D78615 does what this patch wants to do instead?

[fhahn]

In D79748#2030870, @aqjune wrote:

Hi,
There is a relevant ongoing patch : D78615
Would it make sense if D78615 does what this patch wants to do instead?

Ah right this patch is only a subset of D78615. It's probably best to just get D78615 in. I'll commit the additional test separately.

llvm/lib/Analysis/ValueTracking.cpp

bool llvm::propagatesPoison(const Instruction *I) {
   case Instruction::Sub:
   case Instruction::Xor:
   case Instruction::Trunc:
   case Instruction::BitCast:
   case Instruction::AddrSpaceCast:
   case Instruction::Mul:
   case Instruction::Shl:
   case Instruction::GetElementPtr:
+  case Instruction::And:
+  case Instruction::Or:
     // These operations all propagate poison unconditionally. Note that poison
     // is not any particular value, so xor or subtraction of poison with
     // itself still yields poison, not zero.
     return true;
 
   case Instruction::AShr:
   case Instruction::SExt:
     // For these operations, one bit of the input is replicated across

llvm/test/Analysis/ScalarEvolution/nsw.ll

 ; CHECK-NEXT:  -->  {7,+,7}<nuw><%loop>
   %becond = icmp ult i32 %iv, %n
   br i1 %becond, label %loop, label %leave
 
 leave:
   ret void
 }
 
-define void @bad_postinc_nsw_b(i32 %n) {
-; CHECK-LABEL: Classifying expressions for: @bad_postinc_nsw_b
+define void @bad_postinc_nsw_b_or(i32 %n) {
+; CHECK-LABEL: Classifying expressions for: @bad_postinc_nsw_b_or
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ 0, %entry ], [ %iv.inc, %loop ]
+  %iv.inc = add nsw i32 %iv, 7
+  %iv.inc.and = or i32 %iv.inc, 0
+; CHECK:    %iv.inc = add nsw i32 %iv, 7
+; CHECK-NEXT:  -->  {7,+,7}<nuw><nsw><%loop>
+  %becond = icmp ult i32 %iv.inc.and, %n
+  br i1 %becond, label %loop, label %leave
+
+leave:
+  ret void
+}
+
+define void @bad_postinc_nsw_b_and(i32 %n) {
+; CHECK-LABEL: Classifying expressions for: @bad_postinc_nsw_b_and
 entry:
   br label %loop
 
 loop:
   %iv = phi i32 [ 0, %entry ], [ %iv.inc, %loop ]
   %iv.inc = add nsw i32 %iv, 7
   %iv.inc.and = and i32 %iv.inc, 0
 ; CHECK:    %iv.inc = add nsw i32 %iv, 7
-; CHECK-NEXT:  -->  {7,+,7}<nuw><%loop>
+; CHECK-NEXT:  -->  {7,+,7}<nuw><nsw><%loop>
   %becond = icmp ult i32 %iv.inc.and, %n
   br i1 %becond, label %loop, label %leave
 
 leave:
   ret void
 }
 
 declare void @may_exit() nounwind