[RISCV] Fix ISCVISAInfo::computeDefaultABI() result for xcheriot (#212129)

XCheriot was not considered in this function, so RV32E+XCheriot
defaulted
to ilp32e instead of cheriot when no -target-abi was given.

Since this function does not have unit test coverage, this adds new
tests
for the ABI inference functions: RISCVISAInfo::computeDefaultABI() and
RISCVABI::computeTargetABI.

This change was created with the help of AI tools

llvm/lib/TargetParser/RISCVISAInfo.cpp

@@ -1083,6 +1083,8 @@ RISCVISAInfo::postProcessAndChecking(std::unique_ptr<RISCVISAInfo> &&ISAInfo) {
 
 StringRef RISCVISAInfo::computeDefaultABI() const {
   if (XLen == 32) {
+    if (Exts.count("xcheriot"))
+      return "cheriot";
     if (Exts.count("e"))
       return "ilp32e";
     if (Exts.count("d"))

llvm/unittests/Target/RISCV/CMakeLists.txt

@@ -19,6 +19,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_target_unittest(RISCVTests
   MCInstrAnalysisTest.cpp
+  RISCVBaseInfoTest.cpp
   RISCVInstrInfoTest.cpp
   RISCVSelectionDAGTest.cpp
   )

llvm/unittests/Target/RISCV/RISCVBaseInfoTest.cpp

@@ -0,0 +1,50 @@
+//===- RISCVBaseInfoTest.cpp ----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "MCTargetDesc/RISCVBaseInfo.h"
+#include "llvm/MC/MCSubtargetInfo.h"
+#include "llvm/MC/TargetRegistry.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/TargetParser/Triple.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+std::unique_ptr<MCSubtargetInfo> createSTI(StringRef TripleName,
+                                           StringRef FeatureStr) {
+  LLVMInitializeRISCVTargetInfo();
+  LLVMInitializeRISCVTarget();
+  LLVMInitializeRISCVTargetMC();
+  std::string Error;
+  Triple TT(TripleName);
+  const Target *TheTarget = TargetRegistry::lookupTarget(TT, Error);
+  return std::unique_ptr<MCSubtargetInfo>(
+      TheTarget->createMCSubtargetInfo(TT, /*CPU=*/"", FeatureStr));
+}
+
+RISCVABI::ABI computeTargetABI(StringRef TripleName, StringRef FeatureStr,
+                               StringRef ABIName = "") {
+  auto STI = createSTI(TripleName, FeatureStr);
+  return RISCVABI::computeTargetABI(*STI, ABIName);
+}
+
+TEST(ComputeTargetABI, SelectsExpectedABI) {
+  EXPECT_EQ(computeTargetABI("riscv32", ""), RISCVABI::ABI_ILP32);
+  EXPECT_EQ(computeTargetABI("riscv32", "+f"), RISCVABI::ABI_ILP32F);
+  EXPECT_EQ(computeTargetABI("riscv32", "+f,+d"), RISCVABI::ABI_ILP32D);
+  EXPECT_EQ(computeTargetABI("riscv64", ""), RISCVABI::ABI_LP64);
+  EXPECT_EQ(computeTargetABI("riscv64", "+f"), RISCVABI::ABI_LP64F);
+  EXPECT_EQ(computeTargetABI("riscv64", "+f,+d"), RISCVABI::ABI_LP64D);
+
+  // CHERIoT always selects the cheriot ABI by default.
+  EXPECT_EQ(computeTargetABI("riscv32", "+xcheriot"), RISCVABI::ABI_CHERIOT);
+}
+
+} // namespace

llvm/unittests/TargetParser/RISCVISAInfoTest.cpp

@@ -1243,6 +1243,27 @@ TEST(ParseArchString, RVYFeatureImplicationC) {
   EXPECT_FALSE((*MaybeISAInfo)->hasExtension("zcd"));
 }
 
+static StringRef GetABIFromFeatures(unsigned XLen,
+                                    std::vector<std::string> Features) {
+  auto ISAInfo = RISCVISAInfo::parseFeatures(XLen, Features);
+  EXPECT_THAT_EXPECTED(ISAInfo, Succeeded());
+  return (*ISAInfo)->computeDefaultABI();
+}
+
+TEST(ComputeDefaultABI, SelectsExpectedABI) {
+  EXPECT_EQ(GetABIFromFeatures(32, {}), "ilp32");
+  EXPECT_EQ(GetABIFromFeatures(32, {"+f"}), "ilp32f");
+  EXPECT_EQ(GetABIFromFeatures(32, {"+f", "+d"}), "ilp32d");
+  EXPECT_EQ(GetABIFromFeatures(32, {"+e"}), "ilp32e");
+  EXPECT_EQ(GetABIFromFeatures(64, {}), "lp64");
+  EXPECT_EQ(GetABIFromFeatures(64, {"+f"}), "lp64f");
+  EXPECT_EQ(GetABIFromFeatures(64, {"+f", "+d"}), "lp64d");
+  EXPECT_EQ(GetABIFromFeatures(64, {"+e"}), "lp64e");
+
+  // CHERIoT always selects the cheriot ABI by default.
+  EXPECT_EQ(GetABIFromFeatures(32, {"+xcheriot"}), "cheriot");
+}
+
 TEST(ParseArchString, ZcaZcbZcmpZcmtImpliesZce) {
   // Test Zca+Zcb+Zcmp+Zcmt implies Zce behavior.