[AArch64][AsmParser] Add rcpc support in .arch_extension

AArch64 does not support enabling rcpc via .arch_extension in assembly.
GCC, on the other hand, does.

This patch adds 'rcpc' as a valid value to .arch_extension handling.

Differential Revision: https://reviews.llvm.org/D83685

lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

@@ -2844,6 +2844,7 @@ static const struct Extension {
     {"tlb-rmi", {AArch64::FeatureTLB_RMI}},
     {"pan-rwv", {AArch64::FeaturePAN_RWV}},
     {"ccpp", {AArch64::FeatureCCPP}},
+    {"rcpc", {AArch64::FeatureRCPC}},
     {"sve", {AArch64::FeatureSVE}},
     {"sve2", {AArch64::FeatureSVE2}},
     {"sve2-aes", {AArch64::FeatureSVE2AES}},

test/MC/AArch64/directive-arch_extension-negative.s

@@ -78,3 +78,8 @@ at s1e1wp, x2
 dc cvap, x7
 // CHECK: error: DC CVAP requires ccpp
 // CHECK-NEXT: dc cvap, x7
+
+.arch_extension norcpc
+ldapr x0, [x1]
+// CHECK: error: instruction requires: rcpc
+// CHECK-NEXT: ldapr x0, [x1]

test/MC/AArch64/directive-arch_extension.s

@@ -59,3 +59,7 @@ at s1e1wp, x2
 .arch_extension ccpp
 dc cvap, x7
 // CHECK: dc cvap, x7
+
+.arch_extension rcpc
+ldapr x0, [x1]
+// CHECK: ldapr x0, [x1]