[RISCV] Emitting proper atomic ABI tag when Zalasr is enabled

[mehnadnerd]

When Zalasr is enabled, it will emit the A7 atomic ABI tag. Zalasr is the load-acquire and store-release extension, and the reason A7 (and A6S) exists is to support it.
The A7 atomic ABI is compatible with A6S (which is what is currently emitted as the tag), but A7 is not compatible with A6C, while A6C and A6S are compatible.

https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-atomic.adoc#risc-v-atomics-mappings

https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc#tag_riscv_atomic_abi-14-uleb128version

[llvmbot]

@llvm/pr-subscribers-backend-risc-v

Author: Brendan Sweeney (mehnadnerd)

Changes

When Zalasr is enabled, it will emit the A7 atomic ABI tag.

---

Full diff: https://github.com/llvm/llvm-project/pull/121017.diff

1 Files Affected:

• (modified) llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp (+5-3)

diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp
index 99f57f47835abd..6035dffaa8ac8e 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp
@@ -86,9 +86,11 @@ void RISCVTargetStreamer::emitTargetAttributes(const MCSubtargetInfo &STI,
 
   if (RiscvAbiAttr && STI.hasFeature(RISCV::FeatureStdExtA)) {
     unsigned AtomicABITag = static_cast<unsigned>(
-        STI.hasFeature(RISCV::FeatureNoTrailingSeqCstFence)
-            ? RISCVAttrs::RISCVAtomicAbiTag::A6C
-            : RISCVAttrs::RISCVAtomicAbiTag::A6S);
+        STI.hasFeature(RISCV::FeatureStdExtZalasr)
+            ? RISCVAttrs::RISCVAtomicAbiTag::A7
+            : STI.hasFeature(RISCV::FeatureNoTrailingSeqCstFence)
+              ? RISCVAttrs::RISCVAtomicAbiTag::A6C
+              : RISCVAttrs::RISCVAtomicAbiTag::A6S);
     emitAttribute(RISCVAttrs::ATOMIC_ABI, AtomicABITag);
   }
 }

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[mehnadnerd]

Still upgrading tests

[mehnadnerd]

Everything should be ready now. I don't have write access so please land it once you are done reviewing it.

[preames]

LGTM

[preames]

FYI, I have spoken with @mehnadnerd offline. He does not have commit access, and has asked me to land this on his behalf after approval. I'm going to give it until Monday in case any other reviewers have comments, and then land.

[topperc]

LGTM