diff --git a/llvm/lib/Target/LoongArch/AsmParser/LoongArchAsmParser.cpp b/llvm/lib/Target/LoongArch/AsmParser/LoongArchAsmParser.cpp
index cfbff3e91b0c5..96eb8b1b0528a 100644
--- a/llvm/lib/Target/LoongArch/AsmParser/LoongArchAsmParser.cpp
+++ b/llvm/lib/Target/LoongArch/AsmParser/LoongArchAsmParser.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "MCTargetDesc/LoongArchBaseInfo.h"
 #include "MCTargetDesc/LoongArchInstPrinter.h"
 #include "MCTargetDesc/LoongArchMCExpr.h"
 #include "MCTargetDesc/LoongArchMCTargetDesc.h"
@@ -1560,18 +1561,14 @@ bool LoongArchAsmParser::processInstruction(MCInst &Inst, SMLoc IDLoc,
 
 unsigned LoongArchAsmParser::checkTargetMatchPredicate(MCInst &Inst) {
   unsigned Opc = Inst.getOpcode();
+  const MCInstrDesc &MCID = MII.get(Opc);
   switch (Opc) {
   default:
-    if (Opc >= LoongArch::AMCAS_B && Opc <= LoongArch::AMCAS__DB_W) {
+    if (LoongArchII::isSubjectToAMORdConstraint(MCID.TSFlags)) {
+      const bool IsAMCAS = LoongArchII::isAMCAS(MCID.TSFlags);
       MCRegister Rd = Inst.getOperand(0).getReg();
-      MCRegister Rk = Inst.getOperand(2).getReg();
-      MCRegister Rj = Inst.getOperand(3).getReg();
-      if ((Rd == Rk || Rd == Rj) && Rd != LoongArch::R0)
-        return Match_RequiresAMORdDifferRkRj;
-    } else if (Opc >= LoongArch::AMADD_D && Opc <= LoongArch::AMXOR_W) {
-      MCRegister Rd = Inst.getOperand(0).getReg();
-      MCRegister Rk = Inst.getOperand(1).getReg();
-      MCRegister Rj = Inst.getOperand(2).getReg();
+      MCRegister Rk = Inst.getOperand(IsAMCAS ? 2 : 1).getReg();
+      MCRegister Rj = Inst.getOperand(IsAMCAS ? 3 : 2).getReg();
       if ((Rd == Rk || Rd == Rj) && Rd != LoongArch::R0)
         return Match_RequiresAMORdDifferRkRj;
     }
diff --git a/llvm/lib/Target/LoongArch/LoongArchInstrFormats.td b/llvm/lib/Target/LoongArch/LoongArchInstrFormats.td
index 6ffc8823baee0..eee297d2e2d91 100644
--- a/llvm/lib/Target/LoongArch/LoongArchInstrFormats.td
+++ b/llvm/lib/Target/LoongArch/LoongArchInstrFormats.td
@@ -32,6 +32,14 @@ class LAInst<dag outs, dag ins, string opcstr, string opnstr,
   let InOperandList = ins;
   let AsmString = opcstr # "\t" # opnstr;
   let Pattern = pattern;
+
+  // Target-specific instruction info and defaults
+
+  bit IsSubjectToAMORdConstraint = 0;
+  let TSFlags{0} = IsSubjectToAMORdConstraint;
+
+  bit IsAMCAS = 0;
+  let TSFlags{1} = IsAMCAS;
 }
 
 // Pseudo instructions
diff --git a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td
index 4c6028b57e04d..cd1500229f4aa 100644
--- a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td
+++ b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td
@@ -711,15 +711,21 @@ class STORE_2RI14<bits<32> op>
 } // hasSideEffects = 0, mayLoad = 0, mayStore = 1
 
 let hasSideEffects = 0, mayLoad = 1, mayStore = 1,
-    Constraints = "@earlyclobber $rd" in class AM_3R<bits<32> op>
+    IsSubjectToAMORdConstraint = 1 in {
+class AM_3R<bits<32> op>
     : Fmt3R<op, (outs GPR:$rd), (ins GPR:$rk, GPRMemAtomic:$rj),
-            "$rd, $rk, $rj">;
+            "$rd, $rk, $rj"> {
+  let Constraints = "@earlyclobber $rd";
+}
 
-let hasSideEffects = 0, mayLoad = 1, mayStore = 1,
-    Constraints =
-        "@earlyclobber $rd_wb, $rd_wb = $rd" in class AMCAS_3R<bits<32> op>
+class AMCAS_3R<bits<32> op>
     : Fmt3R<op, (outs GPR:$rd_wb), (ins GPR:$rd, GPR:$rk, GPRMemAtomic:$rj),
-            "$rd, $rk, $rj">;
+            "$rd, $rk, $rj"> {
+  let Constraints = "@earlyclobber $rd_wb, $rd_wb = $rd";
+  let IsAMCAS = 1;
+}
+} // hasSideEffects = 0, mayLoad = 1, mayStore = 1,
+  // IsSubjectToAMORdConstraint = 1
 
 let hasSideEffects = 0, mayLoad = 1, mayStore = 0 in {
 class LLBase<bits<32> op>
diff --git a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchBaseInfo.h b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchBaseInfo.h
index 1a12fb492a60f..bd63c5edeabca 100644
--- a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchBaseInfo.h
+++ b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchBaseInfo.h
@@ -56,6 +56,36 @@ enum {
   MO_DESC_CALL,
   // TODO: Add more flags.
 };
+
+// Target-specific flags of LAInst.
+// All definitions must match LoongArchInstrFormats.td.
+enum {
+  // Whether the instruction's rd is normally required to differ from rj and
+  // rk, in the way the 3-register atomic memory operations behave
+  // (Section 2.2.7.1 and 2.2.7.2, LoongArch Reference Manual Volume 1 v1.10;
+  // while Section 2.2.7.3 lacked similar description for the AMCAS
+  // instructions, at least the INE exception is still signaled on Loongson
+  // 3A6000 when its rd == rj).
+  //
+  // Used for generating diagnostics for assembler input that violate the
+  // constraint. As described on the manual, the covered instructions require
+  // rd != rj && rd != rk to work as intended.
+  IsSubjectToAMORdConstraintShift = 0,
+  IsSubjectToAMORdConstraintMask = 1 << IsSubjectToAMORdConstraintShift,
+
+  // Whether the instruction belongs to the AMCAS family.
+  IsAMCASShift = IsSubjectToAMORdConstraintShift + 1,
+  IsAMCASMask = 1 << IsAMCASShift,
+};
+
+/// \returns true if this instruction's rd is normally required to differ
+/// from rj and rk, in the way 3-register atomic memory operations behave.
+static inline bool isSubjectToAMORdConstraint(uint64_t TSFlags) {
+  return TSFlags & IsSubjectToAMORdConstraintMask;
+}
+
+/// \returns true if this instruction belongs to the AMCAS family.
+static inline bool isAMCAS(uint64_t TSFlags) { return TSFlags & IsAMCASMask; }
 } // end namespace LoongArchII
 
 namespace LoongArchABI {
diff --git a/llvm/test/MC/LoongArch/Basic/Integer/invalid64.s b/llvm/test/MC/LoongArch/Basic/Integer/invalid64.s
index 1c1c658ad440f..0d81ddd6763b5 100644
--- a/llvm/test/MC/LoongArch/Basic/Integer/invalid64.s
+++ b/llvm/test/MC/LoongArch/Basic/Integer/invalid64.s
@@ -91,3 +91,14 @@ amxor.w $a0, $a1, $a0
 amadd.d $a0, $a1, $a2, $a3
 # CHECK: :[[#@LINE+1]]:24: error: optional integer offset must be 0
 amadd.d $a0, $a1, $a2, 1
+
+## According to experiment results on real LA664 HW, the AMCAS instructions
+## are subject to the same constraint as the other 3-register atomic insns.
+## This is undocumented in v1.10 of the LoongArch Reference Manual.
+
+# CHECK: :[[#@LINE+1]]:10: error: $rd must be different from both $rk and $rj
+amcas.b $a0, $a0, $a0
+# CHECK: :[[#@LINE+1]]:10: error: $rd must be different from both $rk and $rj
+amcas.h $a0, $a0, $a1
+# CHECK: :[[#@LINE+1]]:13: error: $rd must be different from both $rk and $rj
+amcas_db.w $a0, $a1, $a0