Alternative fix for ARM64 signed small type cmpxchg without LSE (#97902)

* Alternative fix for ARM64 signed small type cmpxchg without LSE Better fix for #97839. * Update importercalls.cpp * Update importercalls.cpp * Add comment
dotnet · Feb 19, 2024 · b473606 · b473606
1 parent 1be948c
commit b473606
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diff --git a/src/coreclr/jit/gtlist.h b/src/coreclr/jit/gtlist.h
@@ -76,7 +76,7 @@ GTNODE(XAND             , GenTreeOp          ,0,1,GTK_BINOP)
 GTNODE(XORR             , GenTreeOp          ,0,1,GTK_BINOP)
 GTNODE(XADD             , GenTreeOp          ,0,1,GTK_BINOP)
 GTNODE(XCHG             , GenTreeOp          ,0,1,GTK_BINOP)
-GTNODE(CMPXCHG          , GenTreeCmpXchg     ,0,1,GTK_SPECIAL)
+GTNODE(CMPXCHG          , GenTreeCmpXchg     ,0,1,GTK_SPECIAL)            // atomic CAS, small types need the comparand to be zero extended
 
 GTNODE(IND              , GenTreeIndir       ,0,1,GTK_UNOP)                                 // Load indirection
 GTNODE(STOREIND         , GenTreeStoreInd    ,0,1,GTK_BINOP|GTK_EXOP|GTK_NOVALUE|GTK_STORE) // Store indirection

diff --git a/src/coreclr/jit/importercalls.cpp b/src/coreclr/jit/importercalls.cpp
@@ -3470,6 +3470,11 @@ GenTree* Compiler::impIntrinsic(GenTree*                newobjThis,
                 assert(sig->numArgs == 3);
 
                 GenTree* op3 = impPopStack().val; // comparand
+                if (varTypeIsSmall(callType))
+                {
+                    // small types need the comparand to have its upper bits zeroed
+                    op3 = gtNewCastNode(genActualType(callType), op3, /* uns */ false, varTypeToUnsigned(callType));
+                }
                 GenTree* op2 = impPopStack().val; // value
                 GenTree* op1 = impPopStack().val; // location
                 retNode      = gtNewAtomicNode(GT_CMPXCHG, callType, op1, op2, op3);