[llvm-branch-commits] [RISCV][lld] Support merging RISC-V Atomics ABI attributes (PR #97347)

[Fangrui Song via llvm-branch-commits]

================
@@ -1084,10 +1084,76 @@ static void 
mergeArch(RISCVISAUtils::OrderedExtensionMap &mergedExts,
   }
 }
 
+static void mergeAtomic(DenseMap<unsigned, unsigned>::iterator it,
+                        const InputSectionBase *oldSection,
+                        const InputSectionBase *newSection,
+                        RISCVAttrs::RISCVAtomicAbiTag oldTag,
+                        RISCVAttrs::RISCVAtomicAbiTag newTag) {
+  using RISCVAttrs::RISCVAtomicAbiTag;
+  // Same tags stay the same, and UNKNOWN is compatible with anything
+  if (oldTag == newTag || newTag == RISCVAtomicAbiTag::UNKNOWN)
+    return;
+
+  auto reportAbiError = [&]() {
+    errorOrWarn("atomic abi mismatch for " + oldSection->name + "\n>>> " +
+                toString(oldSection) +
+                ": atomic_abi=" + Twine(static_cast<unsigned>(oldTag)) +
+                "\n>>> " + toString(newSection) +
+                ": atomic_abi=" + Twine(static_cast<unsigned>(newTag)));
+  };
+
+  switch (static_cast<RISCVAtomicAbiTag>(oldTag)) {
+  case RISCVAtomicAbiTag::UNKNOWN:
+    it->getSecond() = static_cast<unsigned>(newTag);
+    return;
+  case RISCVAtomicAbiTag::A6C:
+    switch (newTag) {
+    case RISCVAtomicAbiTag::A6S:
+      it->getSecond() = static_cast<unsigned>(RISCVAtomicAbiTag::A6C);
+      return;
+    case RISCVAtomicAbiTag::A7:
+      reportAbiError();
+      return;
+    case RISCVAttrs::RISCVAtomicAbiTag::UNKNOWN:
+    case RISCVAttrs::RISCVAtomicAbiTag::A6C:
+      return;
+    };
+
+  case RISCVAtomicAbiTag::A6S:
+    switch (newTag) {
+    case RISCVAtomicAbiTag::A6C:
+      it->getSecond() = static_cast<unsigned>(RISCVAtomicAbiTag::A6C);
+      return;
+    case RISCVAtomicAbiTag::A7:
+      it->getSecond() = static_cast<unsigned>(RISCVAtomicAbiTag::A7);
+      return;
+    case RISCVAttrs::RISCVAtomicAbiTag::UNKNOWN:
+    case RISCVAttrs::RISCVAtomicAbiTag::A6S:
+      return;
+    };
+
+  case RISCVAtomicAbiTag::A7:
+    switch (newTag) {
+    case RISCVAtomicAbiTag::A6S:
+      it->getSecond() = static_cast<unsigned>(RISCVAtomicAbiTag::A7);
+      return;
+    case RISCVAtomicAbiTag::A6C:
+      reportAbiError();
+      return;
+    case RISCVAttrs::RISCVAtomicAbiTag::UNKNOWN:
+    case RISCVAttrs::RISCVAtomicAbiTag::A7:
+      return;
+    };
+  };
+  llvm_unreachable("unknown AtomicABI");
----------------
MaskRay wrote:

If a potentially-corrupted object file may contain an unknown tag, it's 
inappropriate to use unreachable. 

https://github.com/llvm/llvm-project/pull/97347
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