Assert instead of normalizing

Instead of normalizing GTF_UNSIGNED for FP sources in "gtNewCastNode",
assert that it is not set in GenTreeCast's constructor and fix the
importer to respect that constraint.

Author: SingleAccretion

src/coreclr/jit/compiler.hpp

@@ -1410,18 +1410,9 @@ inline void GenTree::SetOper(genTreeOps oper, ValueNumberUpdate vnUpdate)
     }
 }
 
-inline void CanonicalizeCastNode(GenTreeCast* cast)
-{
-    if (varTypeIsFloating(cast->CastOp()))
-    {
-        cast->gtFlags &= ~GTF_UNSIGNED;
-    }
-}
-
 inline GenTreeCast* Compiler::gtNewCastNode(var_types typ, GenTree* op1, bool fromUnsigned, var_types castType)
 {
     GenTreeCast* cast = new (this, GT_CAST) GenTreeCast(typ, op1, fromUnsigned, castType);
-    CanonicalizeCastNode(cast);
 
     return cast;
 }
@@ -1437,7 +1428,6 @@ inline GenTreeCast* Compiler::gtNewCastNodeL(var_types typ, GenTree* op1, bool f
 
     GenTreeCast* cast =
         new (this, LargeOpOpcode()) GenTreeCast(typ, op1, fromUnsigned, castType DEBUGARG(/*largeNode*/ true));
-    CanonicalizeCastNode(cast);
 
     return cast;
 }

src/coreclr/jit/gentree.h

@@ -3531,6 +3531,11 @@ struct GenTreeCast : public GenTreeOp
     GenTreeCast(var_types type, GenTree* op, bool fromUnsigned, var_types castType DEBUGARG(bool largeNode = false))
         : GenTreeOp(GT_CAST, type, op, nullptr DEBUGARG(largeNode)), gtCastType(castType)
     {
+        // We do not allow casts from floating point types to be treated as from
+        // unsigned to avoid bugs related to wrong GTF_UNSIGNED in case the
+        // CastOp's type changes.
+        assert(!varTypeIsFloating(op) || !fromUnsigned);
+
         gtFlags |= fromUnsigned ? GTF_UNSIGNED : GTF_EMPTY;
     }
 #if DEBUGGABLE_GENTREE

src/coreclr/jit/importer.cpp

@@ -13456,11 +13456,17 @@ void Compiler::impImportBlockCode(BasicBlock* block)
                     callNode = varTypeIsFloating(impStackTop().val->TypeGet());
                 }
 
-                // At this point uns, ovf, callNode are all set.
-
                 op1 = impPopStack().val;
                 impBashVarAddrsToI(op1);
 
+                // Casts from floating point types must not have GTF_UNSIGNED set.
+                if (varTypeIsFloating(op1))
+                {
+                    uns = false;
+                }
+
+                // At this point uns, ovf, callNode are all set.
+
                 if (varTypeIsSmall(lclTyp) && !ovfl && op1->gtType == TYP_INT && op1->gtOper == GT_AND)
                 {
                     op2 = op1->AsOp()->gtOp2;