[RISCV] Limit VLEN in getOptimalMemOpType to prevent creating invalid MVTs.

[topperc]

We only guarantee that types that are 1024 bytes or smaller exist in the MVT enum.

Fixes #139075.

[llvmbot]

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

Author: Craig Topper (topperc)

Changes

We only guarantee that types that are 1024 bytes or smaller exist in the MVT enum.

Fixes #139075.

---

Full diff: https://github.com/llvm/llvm-project/pull/139116.diff

1 Files Affected:

• (modified) llvm/lib/Target/RISCV/RISCVISelLowering.cpp (+3-1)

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index f2bc1765bc4c6..1bc601a0c399d 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -23487,7 +23487,9 @@ EVT RISCVTargetLowering::getOptimalMemOpType(const MemOp &Op,
   // combining will typically form larger LMUL operations from the LMUL1
   // operations emitted here, and that's okay because combining isn't
   // introducing new memory operations; it's just merging existing ones.
-  const unsigned MinVLenInBytes = Subtarget.getRealMinVLen()/8;
+  // NOTE: We limit to 1024 bytes to avoid creating an invalid MVT.
+  const unsigned MinVLenInBytes = std::min(Subtarget.getRealMinVLen()/8, 1024U);
+
   if (Op.size() < MinVLenInBytes)
     // TODO: Figure out short memops.  For the moment, do the default thing
     // which ends up using scalar sequences.

[github-actions]

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

[preames]

LGTM.

Please add a test if you can reduce one.

[topperc]

LGTM.

Please add a test if you can reduce one.

I made one, but I forgot git add. Brain fog from moving I guess.