[SCCP] Add support for trunc nuw range.

Author: andjo403

llvm/lib/Transforms/Utils/SCCPSolver.cpp

@@ -1442,8 +1442,12 @@ void SCCPInstVisitor::visitCastInst(CastInst &I) {
         OpSt.asConstantRange(I.getSrcTy(), /*UndefAllowed=*/false);
 
     Type *DestTy = I.getDestTy();
-    ConstantRange Res =
-        OpRange.castOp(I.getOpcode(), DestTy->getScalarSizeInBits());
+    ConstantRange Res = ConstantRange::getEmpty(DestTy->getScalarSizeInBits());
+    if (auto *Trunc = dyn_cast<TruncInst>(&I))
+      Res = OpRange.truncate(DestTy->getScalarSizeInBits(),
+                             Trunc->getNoWrapKind());
+    else
+      Res = OpRange.castOp(I.getOpcode(), DestTy->getScalarSizeInBits());
     mergeInValue(LV, &I, ValueLatticeElement::getRange(Res));
   } else
     markOverdefined(&I);

llvm/test/Transforms/SCCP/conditions-ranges.ll

@@ -1441,8 +1441,7 @@ define void @trunc_nuw_i1_dominating_icmp_ne_0(i8 %x) {
 ; CHECK-NEXT:    [[ICMP:%.*]] = icmp ne i8 [[X:%.*]], 0
 ; CHECK-NEXT:    br i1 [[ICMP]], label [[BB1:%.*]], label [[BB2:%.*]]
 ; CHECK:       bb1:
-; CHECK-NEXT:    [[C1:%.*]] = trunc nuw i8 [[X]] to i1
-; CHECK-NEXT:    call void @use(i1 [[C1]])
+; CHECK-NEXT:    call void @use(i1 true)
 ; CHECK-NEXT:    ret void
 ; CHECK:       bb2:
 ; CHECK-NEXT:    ret void