Constant folding for RuntimeInformation.IsOSPlatform(OSPlatform) (#83308)

Author: EgorBo

src/coreclr/jit/importervectorization.cpp

@@ -731,10 +731,8 @@ GenTree* Compiler::impStringEqualsOrStartsWith(bool startsWith, CORINFO_SIG_INFO
     GenTreeLclVar* varStrLcl   = gtNewLclvNode(varStrTmp, varStr->TypeGet());
 
     // Create a tree representing string's Length:
-    // TODO-Unroll-CQ: Consider using ARR_LENGTH here, but we'll have to modify QMARK to propagate BBF_HAS_IDX_LEN
     int      strLenOffset = OFFSETOF__CORINFO_String__stringLen;
-    GenTree* lenOffset    = gtNewIconNode(strLenOffset, TYP_I_IMPL);
-    GenTree* lenNode      = gtNewIndir(TYP_INT, gtNewOperNode(GT_ADD, TYP_BYREF, varStrLcl, lenOffset));
+    GenTree* lenNode      = gtNewArrLen(TYP_INT, varStrLcl, strLenOffset, compCurBB);
     varStrLcl             = gtClone(varStrLcl)->AsLclVar();
 
     GenTree* unrolled = impExpandHalfConstEquals(varStrLcl, lenNode, needsNullcheck, startsWith, (WCHAR*)str, cnsLength,

src/coreclr/jit/morph.cpp

@@ -14544,8 +14544,10 @@ void Compiler::fgExpandQmarkStmt(BasicBlock* block, Statement* stmt)
     // if they are going to be cleared by fgSplitBlockAfterStatement(). We currently only do this only
     // for the GC safe point bit, the logic being that if 'block' was marked gcsafe, then surely
     // remainderBlock will still be GC safe.
-    BasicBlockFlags propagateFlags = block->bbFlags & BBF_GC_SAFE_POINT;
-    BasicBlock*     remainderBlock = fgSplitBlockAfterStatement(block, stmt);
+    BasicBlockFlags propagateFlagsToRemainder = block->bbFlags & BBF_GC_SAFE_POINT;
+    // Conservatively propagate BBF_COPY_PROPAGATE flags to all blocks
+    BasicBlockFlags propagateFlagsToAll = block->bbFlags & BBF_COPY_PROPAGATE;
+    BasicBlock*     remainderBlock      = fgSplitBlockAfterStatement(block, stmt);
     fgRemoveRefPred(remainderBlock, block); // We're going to put more blocks between block and remainderBlock.
 
     BasicBlock* condBlock = fgNewBBafter(BBJ_COND, block, true);
@@ -14561,14 +14563,17 @@ void Compiler::fgExpandQmarkStmt(BasicBlock* block, Statement* stmt)
         elseBlock->bbFlags |= BBF_IMPORTED;
     }
 
-    remainderBlock->bbFlags |= propagateFlags;
+    remainderBlock->bbFlags |= (propagateFlagsToRemainder | propagateFlagsToAll);
 
     condBlock->inheritWeight(block);
 
     fgAddRefPred(condBlock, block);
     fgAddRefPred(elseBlock, condBlock);
     fgAddRefPred(remainderBlock, elseBlock);
 
+    condBlock->bbFlags |= propagateFlagsToAll;
+    elseBlock->bbFlags |= propagateFlagsToAll;
+
     BasicBlock* thenBlock = nullptr;
     if (hasTrueExpr && hasFalseExpr)
     {
@@ -14585,6 +14590,7 @@ void Compiler::fgExpandQmarkStmt(BasicBlock* block, Statement* stmt)
 
         thenBlock             = fgNewBBafter(BBJ_ALWAYS, condBlock, true);
         thenBlock->bbJumpDest = remainderBlock;
+        thenBlock->bbFlags |= propagateFlagsToAll;
         if ((block->bbFlags & BBF_INTERNAL) == 0)
         {
             thenBlock->bbFlags &= ~BBF_INTERNAL;

src/libraries/System.Private.CoreLib/src/System/OperatingSystem.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
+using System.Runtime.CompilerServices;
 using System.Runtime.Serialization;
 using System.Runtime.Versioning;
 
@@ -115,6 +116,7 @@ public string VersionString
         /// Indicates whether the current application is running on the specified platform.
         /// </summary>
         /// <param name="platform">Case-insensitive platform name. Examples: Browser, Linux, FreeBSD, Android, iOS, macOS, tvOS, watchOS, Windows.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static bool IsOSPlatform(string platform)
         {
             ArgumentNullException.ThrowIfNull(platform);