[ConstantRange] Allow casting to the same bitwidth. NFC (llvm#170102)

From the review in
llvm#169527 (comment),
there are some users where we want to extend or truncate a ConstantRange
only if it's not already the destination bitwidth. Previously this
asserted, so this PR relaxes it to just be a no-op, similar to
IRBuilder::createZExt and friends.

Author: lukel97

llvm/lib/IR/ConstantRange.cpp

@@ -841,6 +841,8 @@ ConstantRange ConstantRange::zeroExtend(uint32_t DstTySize) const {
   if (isEmptySet()) return getEmpty(DstTySize);
 
   unsigned SrcTySize = getBitWidth();
+  if (DstTySize == SrcTySize)
+    return *this;
   assert(SrcTySize < DstTySize && "Not a value extension");
   if (isFullSet() || isUpperWrapped()) {
     // Change into [0, 1 << src bit width)
@@ -858,6 +860,8 @@ ConstantRange ConstantRange::signExtend(uint32_t DstTySize) const {
   if (isEmptySet()) return getEmpty(DstTySize);
 
   unsigned SrcTySize = getBitWidth();
+  if (DstTySize == SrcTySize)
+    return *this;
   assert(SrcTySize < DstTySize && "Not a value extension");
 
   // special case: [X, INT_MIN) -- not really wrapping around
@@ -874,6 +878,8 @@ ConstantRange ConstantRange::signExtend(uint32_t DstTySize) const {
 
 ConstantRange ConstantRange::truncate(uint32_t DstTySize,
                                       unsigned NoWrapKind) const {
+  if (DstTySize == getBitWidth())
+    return *this;
   assert(getBitWidth() > DstTySize && "Not a value truncation");
   if (isEmptySet())
     return getEmpty(DstTySize);

llvm/lib/Transforms/Utils/SCCPSolver.cpp

@@ -2109,10 +2109,10 @@ void SCCPInstVisitor::handleCallResult(CallBase &CB) {
 
       ConstantRange Count = getValueState(CountArg)
                                 .asConstantRange(CountArg->getType(), false)
-                                .zextOrTrunc(BitWidth);
+                                .zeroExtend(BitWidth);
       ConstantRange MaxLanes = getValueState(VF)
                                    .asConstantRange(VF->getType(), false)
-                                   .zextOrTrunc(BitWidth);
+                                   .zeroExtend(BitWidth);
       if (Scalable)
         MaxLanes =
             MaxLanes.multiply(getVScaleRange(II->getFunction(), BitWidth));
@@ -2126,7 +2126,7 @@ void SCCPInstVisitor::handleCallResult(CallBase &CB) {
       if (Count.icmp(CmpInst::ICMP_ULE, MaxLanes))
         Result = Count;
 
-      Result = Result.zextOrTrunc(II->getType()->getScalarSizeInBits());
+      Result = Result.truncate(II->getType()->getScalarSizeInBits());
       return (void)mergeInValue(ValueState[II], II,
                                 ValueLatticeElement::getRange(Result));
     }

llvm/unittests/IR/ConstantRangeTest.cpp

@@ -449,6 +449,9 @@ TEST_F(ConstantRangeTest, Trunc) {
   // trunc([7, 1), 3->2) = [3, 1)
   ConstantRange SevenOne(APInt(3, 7), APInt(3, 1));
   EXPECT_EQ(SevenOne.truncate(2), ConstantRange(APInt(2, 3), APInt(2, 1)));
+
+  ConstantRange Nop = Full.truncate(Full.getBitWidth());
+  EXPECT_EQ(Full, Nop);
 }
 
 TEST_F(ConstantRangeTest, TruncNuw) {
@@ -527,6 +530,9 @@ TEST_F(ConstantRangeTest, ZExt) {
   // zext([5, 0), 3->7) = [5, 8)
   ConstantRange FiveZero(APInt(3, 5), APInt(3, 0));
   EXPECT_EQ(FiveZero.zeroExtend(7), ConstantRange(APInt(7, 5), APInt(7, 8)));
+
+  ConstantRange Nop = Full.zeroExtend(Full.getBitWidth());
+  EXPECT_EQ(Full, Nop);
 }
 
 TEST_F(ConstantRangeTest, SExt) {
@@ -550,6 +556,9 @@ TEST_F(ConstantRangeTest, SExt) {
 
   EXPECT_EQ(ConstantRange(APInt(16, 0x0200), APInt(16, 0x8000)).signExtend(19),
             ConstantRange(APInt(19, 0x0200), APInt(19, 0x8000)));
+
+  ConstantRange Nop = Full.signExtend(Full.getBitWidth());
+  EXPECT_EQ(Full, Nop);
 }
 
 TEST_F(ConstantRangeTest, IntersectWith) {