[SCCP] Don't always set MayIncludeUndef as true when calling markConstant

[StephenFan]

Summary

In markConstant, MayIncludeUndef makes a difference when the Constant is
ConstantInt. Currently we hard code MayIncludeUndef as true, but in fact
only when there is at least one operand has
constantrange_including_undef, the simplifed result can
MayIncludingUndef.

llvm/lib/Transforms/Utils/SCCPSolver.cpp

if (SCCPSolver::isConstant(V1State) || SCCPSolver::isConstant(V2State)) {
     auto *C = dyn_cast_or_null<Constant>(R);
     if (C) {
       // Conservatively assume that the result may be based on operands that may
       // be undef. Note that we use mergeInValue to combine the constant with
       // the existing lattice value for I, as different constants might be found
       // after one of the operands go to overdefined, e.g. due to one operand
       // being a special floating value.
       ValueLatticeElement NewV;
-      NewV.markConstant(C, /*MayIncludeUndef=*/true);
+      NewV.markConstant(C, V1State.isConstantRangeIncludingUndef() ||
+                               V2State.isConstantRangeIncludingUndef());
       return (void)mergeInValue(&I, NewV);
     }
   }
 
   // Only use ranges for binary operators on integers.
   if (!I.getType()->isIntegerTy())
     return markOverdefined(&I);
 

llvm/test/Transforms/SCCP/ip-ranges-phis.ll

 ; CHECK-NEXT:    [[P:%.*]] = phi i32 [ [[X]], [[ENTRY:%.*]] ], [ [[Y]], [[IF_TRUE_1]] ], [ [[Z]], [[IF_TRUE_2]] ]
 ; CHECK-NEXT:    [[C_1:%.*]] = icmp sgt i32 [[P]], 5
 ; CHECK-NEXT:    [[C_2:%.*]] = icmp eq i32 [[P]], 0
 ; CHECK-NEXT:    [[C_3:%.*]] = icmp slt i32 [[P]], 0
 ; CHECK-NEXT:    [[V_1:%.*]] = select i1 [[C_1]], i32 10, i32 100
 ; CHECK-NEXT:    [[V_2:%.*]] = select i1 [[C_2]], i32 20, i32 200
 ; CHECK-NEXT:    [[V_3:%.*]] = select i1 [[C_3]], i32 30, i32 300
 ; CHECK-NEXT:    [[R_1:%.*]] = add nuw nsw i32 [[V_1]], [[V_2]]
-; CHECK-NEXT:    [[R_2:%.*]] = add i32 [[R_1]], [[V_3]]
-; CHECK-NEXT:    [[R_3:%.*]] = add i32 [[R_2]], 400
-; CHECK-NEXT:    [[R_4:%.*]] = add i32 [[R_3]], 50
-; CHECK-NEXT:    [[R_5:%.*]] = add i32 [[R_4]], 60
-; CHECK-NEXT:    [[R_6:%.*]] = add i32 [[R_4]], 700
+; CHECK-NEXT:    [[R_2:%.*]] = add nuw nsw i32 [[R_1]], [[V_3]]
+; CHECK-NEXT:    [[R_3:%.*]] = add nuw nsw i32 [[R_2]], 400
+; CHECK-NEXT:    [[R_4:%.*]] = add nuw nsw i32 [[R_3]], 50
+; CHECK-NEXT:    [[R_5:%.*]] = add nuw nsw i32 [[R_4]], 60
+; CHECK-NEXT:    [[R_6:%.*]] = add nuw nsw i32 [[R_4]], 700
 ; CHECK-NEXT:    ret i32 [[R_6]]
 ;
 
 
 
 entry:
   br i1 %cmp.1, label %if.true.1, label %end
 

 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br i1 [[CMP_1]], label [[IF_TRUE:%.*]], label [[END:%.*]]
 ; CHECK:       if.true:
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
 ; CHECK-NEXT:    [[P1:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ 1, [[IF_TRUE]] ]
 ; CHECK-NEXT:    [[P2:%.*]] = phi i32 [ 1, [[ENTRY]] ], [ -10, [[IF_TRUE]] ]
 ; CHECK-NEXT:    [[P3:%.*]] = phi i32 [ 1, [[ENTRY]] ], [ 10, [[IF_TRUE]] ]
-; CHECK-NEXT:    [[CALL1:%.*]] = tail call i32 @f2(i32 [[P1]], i32 [[P2]], i32 [[P3]], i1 [[CMP_1]], i1 [[CMP_2]])
+; CHECK-NEXT:    [[CALL1:%.*]] = tail call i32 @f2(i32 [[P1]], i32 [[P2]], i32 [[P3]], i1 [[CMP_1]], i1 [[CMP_2]]), !range [[RNG0:![0-9]+]]
 ; CHECK-NEXT:    ret i32 [[CALL1]]
 ;
 
 
 
 entry:
   br i1 %cmp.1, label %if.true, label %end
 

 ; CHECK-LABEL: define {{[^@]+}}@caller3
 ; CHECK-SAME: (i32 [[Y:%.*]], i1 [[CMP_1:%.*]]) {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br i1 [[CMP_1]], label [[IF_TRUE:%.*]], label [[END:%.*]]
 ; CHECK:       if.true:
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
 ; CHECK-NEXT:    [[P1:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ 5, [[IF_TRUE]] ]
-; CHECK-NEXT:    [[CALL1:%.*]] = tail call i32 @f3(i32 [[P1]], i32 [[Y]], i1 [[CMP_1]]), !range [[RNG0:![0-9]+]]
+; CHECK-NEXT:    [[CALL1:%.*]] = tail call i32 @f3(i32 [[P1]], i32 [[Y]], i1 [[CMP_1]]), !range [[RNG1:![0-9]+]]
 ; CHECK-NEXT:    ret i32 [[CALL1]]
 ;
 
 
 entry:
   br i1 %cmp.1, label %if.true, label %end
 
 if.true:
   br label %end
 
 end:
   %p1 = phi i32 [ 0, %entry], [ 5, %if.true ]
   %call1 = tail call i32 @f3(i32 %p1, i32 %y, i1 %cmp.1)
   ret i32 %call1
 }