[CHERI-RISC-V] In capability mode compressed move is capability move

llvm/lib/Target/RISCV/RISCVInstrInfoC.td

@@ -563,7 +563,7 @@ def C_JR : RVInst16CR<0b1000, 0b10, (outs), (ins GPRNoX0:$rs1),
 }
 
 let hasSideEffects = 0, mayLoad = 0, mayStore = 0, isMoveReg = 1,
-    isAsCheapAsAMove = 1 in
+    isAsCheapAsAMove = 1, Predicates = [HasStdExtCOrZca, NotCapMode] in
 def C_MV : RVInst16CR<0b1000, 0b10, (outs GPRNoX0:$rs1), (ins GPRNoX0:$rs2),
                       "c.mv", "$rs1, $rs2">,
            Sched<[WriteIALU, ReadIALU]>;

llvm/lib/Target/RISCV/RISCVInstrInfoXCheri.td

@@ -1131,6 +1131,12 @@ def C_CSDCSP : CCheriStackStore<0b111, "c.sdsp", GPR, uimm9_lsb000> {
 }
 
 } // Predicates = [HasCheri, HasCheriRVC, HasStdExtC, IsCapMode]
+let hasSideEffects = 0, mayLoad = 0, mayStore = 0, isMoveReg = 1,
+    isAsCheapAsAMove = 1,
+    Predicates = [HasCheri, HasCheriRVC, HasStdExtCOrZca, IsCapMode] in
+def C_CMove : RVInst16CR<0b1000, 0b10, (outs GPCRNoC0:$rs1), (ins GPCRNoC0:$rs2),
+                         "c.cmove", "$rs1, $rs2">,
+           Sched<[WriteIALU, ReadIALU]>;
 } // DecoderNamespace = "CapModeOnly_"
 
 let Predicates = [HasCheri, HasCheriRVC, HasStdExtC, IsCapMode] in {
@@ -1173,6 +1179,11 @@ def : InstAlias<"c.cfsdcsp $rs2, ${imm}(${rs1})", (C_CFSDCSP FPR64:$rs2, CSP:$rs
 def : InstAlias<"c.cj $offset", (C_J simm12_lsb0:$offset), 0>;
 }
 
+let Predicates = [HasCheri, HasCheriRVC, HasStdExtCOrZca, IsCapMode] in {
+def : CompressPat<(CMove GPCRNoC0:$cs1, GPCRNoC0:$cs2),
+                  (C_CMove GPCRNoC0:$cs1, GPCRNoC0:$cs2)>;
+}
+
 //===----------------------------------------------------------------------===//
 // Pseudo-instructions and codegen patterns
 //===----------------------------------------------------------------------===//

llvm/test/MC/RISCV/cheri/compressed-move.s

@@ -0,0 +1,24 @@
+## Check that we don't compress addi 0 to c.mv (which is c.cmove for the RISC-V standard capmode)
+# RUN: llvm-mc %s -triple=riscv64 -mattr=+c,+xcheri,-cap-mode -riscv-no-aliases \
+# RUN:    -show-encoding --defsym=PURECAP=0 | FileCheck %s --check-prefix=INT-MODE
+# RUN: llvm-mc %s -triple=riscv64 -mattr=+c,+xcheri,+cap-mode -riscv-no-aliases \
+# RUN:    -show-encoding --defsym=PURECAP=1 | FileCheck %s --check-prefix=CAP-MODE
+
+# TODO-ISAV9-CAPMODE: c.mv a1, a0    # encoding: [0xaa,0x85]
+# TODO-ISAV9-INTMODE: c.mv a1, a0    # encoding: [0xaa,0x85]
+# CAP-MODE:  addi a1, a0, 0 # encoding: [0x93,0x05,0x05,0x00]
+# INT-MODE:  c.mv a1, a0    # encoding: [0xaa,0x85]
+## Should not be compressed to c.cmove for capability mode (only in integer mode).
+addi a1, a0, 0
+
+# CMove should be compressed for capmode.
+# TODO-ISAV9-CAPMODE: cmove ca1, ca0   # encoding: [0xdb,0x05,0xa5,0xfe]
+# TODO-ISAV9-INTMODE: cmove ca1, ca0   # encoding: [0xdb,0x05,0xa5,0xfe]
+# INT-MODE:  cmove ca1, ca0   # encoding: [0xdb,0x05,0xa5,0xfe]
+# CAP-MODE:  c.cmove ca1, ca0 # encoding: [0xaa,0x85]
+cmove ca1, ca0
+
+.if PURECAP
+# CAP-MODE:  c.cmove ca2, ca0 # encoding: [0x2a,0x86]
+c.cmove ca2, ca0
+.endif