[GlobalISel]: Fix a bug in KnownBits where we should have been using SizeInBits

[aditya_nandakumar]

Summary

We were using getIndexSize instead of getIndexSizeInBits().
Added test case for G_PTRTOINT and G_INTTOPTR.

[bogner]

Obvious bugfixes like this can generally be post-commit reviewed.

[volkan]

LGTM.

[aditya_nandakumar]

368618.

llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp

void GISelKnownBits::computeKnownBitsImpl(Register R, KnownBits &Known,
   case TargetOpcode::G_PTRTOINT:
     // Fall through and handle them the same as zext/trunc.
     LLVM_FALLTHROUGH;
   case TargetOpcode::G_ZEXT:
   case TargetOpcode::G_TRUNC: {
     Register SrcReg = MI.getOperand(1).getReg();
     LLT SrcTy = MRI.getType(SrcReg);
     unsigned SrcBitWidth = SrcTy.isPointer()
-                               ? DL.getIndexSize(SrcTy.getAddressSpace())
+                               ? DL.getIndexSizeInBits(SrcTy.getAddressSpace())
                                : SrcTy.getSizeInBits();
     assert(SrcBitWidth && "SrcBitWidth can't be zero");
     Known = Known.zextOrTrunc(SrcBitWidth, true);
     computeKnownBitsImpl(SrcReg, Known, DemandedElts, Depth + 1);
     Known = Known.zextOrTrunc(BitWidth, true);
     if (BitWidth > SrcBitWidth)
       Known.Zero.setBitsFrom(SrcBitWidth);
     break;

llvm/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp

TEST_F(GISelMITest, TestKnownBitsCst) {
   unsigned CopyReg = Copies[Copies.size() - 1];
   MachineInstr *FinalCopy = MRI->getVRegDef(CopyReg);
   unsigned SrcReg = FinalCopy->getOperand(1).getReg();
   GISelKnownBits Info(*MF);
   KnownBits Res = Info.getKnownBits(SrcReg);
   EXPECT_EQ((uint64_t)1, Res.One.getZExtValue());
   EXPECT_EQ((uint64_t)0xfe, Res.Zero.getZExtValue());
 }
+TEST_F(GISelMITest, TestKnownBitsPtrToIntViceVersa) {
+  StringRef MIRString = "  %3:_(s16) = G_CONSTANT i16 256\n"
+                        "  %4:_(p0) = G_INTTOPTR %3\n"
+                        "  %5:_(s32) = G_PTRTOINT %4\n"
+                        "  %6:_(s32) = COPY %5\n";
+  setUp(MIRString);
+  if (!TM)
+    return;
+  unsigned CopyReg = Copies[Copies.size() - 1];
+  MachineInstr *FinalCopy = MRI->getVRegDef(CopyReg);
+  unsigned SrcReg = FinalCopy->getOperand(1).getReg();
+  GISelKnownBits Info(*MF);
+  KnownBits Res = Info.getKnownBits(SrcReg);
+  EXPECT_EQ(256u, Res.One.getZExtValue());
+  EXPECT_EQ(0xfffffeffu, Res.Zero.getZExtValue());
+}
 
 TEST_F(GISelMITest, TestKnownBits) {
 
   StringRef MIR = "  %3:_(s32) = G_TRUNC %0\n"
                   "  %4:_(s32) = G_TRUNC %1\n"
                   "  %5:_(s32) = G_CONSTANT i32 5\n"
                   "  %6:_(s32) = G_CONSTANT i32 24\n"
                   "  %7:_(s32) = G_CONSTANT i32 28\n"