[llvm] [RISCV]Add support for resolving encoding conflicts among vendor specific CSRs (PR #96174)

[Craig Topper via llvm-commits]

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@@ -0,0 +1,118 @@
+// RUN: llvm-tblgen -gen-searchable-tables -I %p/../../include %s | FileCheck %s
+
+include "llvm/TableGen/SearchableTable.td"
+
+class SysReg<string name, bits<12> op> {
+  string Name = name;
+  bits<12> Encoding = op;
+  code FeaturesRequired = [{ {} }];
+}
+
+def List1 : GenericTable {
+  let FilterClass = "SysReg";
+  let Fields = [
+     "Name", "Encoding", "FeaturesRequired",
+  ];
+
+  let PrimaryKey = [ "Encoding" ];
+  let PrimaryKeyName = "lookupSysRegByEncoding";
+  let PrimaryKeyReturnRange = true;
+}
+
+
+let FeaturesRequired = [{ {Feature1} }] in {
+def : SysReg<"csr1", 0x7C9>;
+}
+
+let FeaturesRequired = [{ {Feature2} }] in {
+def : SysReg<"csr2", 0x7C9>;
+}
+
+// CHECK: #ifdef GET_List1_DECL
+// CHECK-NEXT: std::pair<const SysReg *, const SysReg *>lookupSysRegByEncoding(uint16_t Encoding);
+// CHECK-NEXT: #endif
+
+// CHECK: #ifdef GET_List1_IMPL
+// CHECK-NEXT: constexpr SysReg List1[] = {
+// CHECK-NEXT:   { "csr1", 0x7C9,  {Feature1}  }, // 0
+// CHECK-NEXT:   { "csr2", 0x7C9,  {Feature2}  }, // 1
+// CHECK-NEXT:  };
+
+// CHECK: std::pair<const SysReg *, const SysReg *>lookupSysRegByEncoding(uint16_t Encoding) {
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topperc wrote:

Would it be better to return `llvm::iterator_range` instead of `std::pair`? I think that would make it naturally compatible with range based loops in the caller.

https://github.com/llvm/llvm-project/pull/96174