[lld] [llvm] [RISCV] Support RISCV Atomics ABI attributes (PR #84597)

[Fangrui Song via llvm-commits]

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@@ -1084,10 +1084,62 @@ static void mergeArch(RISCVISAInfo::OrderedExtensionMap &mergedExts,
   }
 }
 
+static void mergeAtomic(DenseMap<unsigned, unsigned>::iterator it,
+                        const InputSectionBase *oldSection,
+                        const InputSectionBase *newSection, unsigned int oldTag,
+                        unsigned int newTag) {
+  using RISCVAttrs::RISCVAtomicAbiTag::AtomicABI;
+  // Same tags stay the same, and UNKNOWN is compatible with anything
+  if (oldTag == newTag || newTag == AtomicABI::UNKNOWN)
+    return;
+
+  switch (oldTag) {
+  case AtomicABI::UNKNOWN:
+    it->getSecond() = newTag;
+    return;
+  case AtomicABI::A6C:
+    switch (newTag) {
+    case AtomicABI::A6S:
+      it->getSecond() = AtomicABI::A6C;
+      return;
+    case AtomicABI::A7:
+      error(toString(oldSection) + " has atomic_abi=" + Twine(oldTag) +
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MaskRay wrote:

This should use `errorOrWarn`.

Sorry that I did not follow up the discussion in time, but I'd appreciate that I had the opportunity to give this comment after the patch was approved by @asb ...

https://github.com/llvm/llvm-project/pull/84597