[llvm] d36b94a - [MIRParser] Reject a one-element fixed-length vector type (#213290)

[via llvm-commits]

Author: Taimuraz Kaitmazov
Date: 2026-09-13T17:05:39Z
New Revision: d36b94ae1dc4a61d3ccff73330adbe571ef1ccd6

URL: https://github.com/llvm/llvm-project/commit/d36b94ae1dc4a61d3ccff73330adbe571ef1ccd6
DIFF: https://github.com/llvm/llvm-project/commit/d36b94ae1dc4a61d3ccff73330adbe571ef1ccd6.diff

LOG: [MIRParser] Reject a one-element fixed-length vector type (#213290)

MIParser accepts `<1 x sN>` and then asserts while building the LLT, so
llc aborts during parsing instead of reporting a parse error:

```
Assertion `!EC.isScalar() && "invalid number of vector elements"' failed.
```

LLT has no one-element fixed-length vector. `getLLTForType`,
`getLLTForMVT` and
`LLT::changeElementCount` all map a one-element `ElementCount` to the
element
type through `LLT::scalarOrVector`, nothing calls `LLT::fixed_vector(1,
...)`,
and no in-tree .mir test uses the syntax. `verifyVectorElementCount`
already rejects 0 and anything above 2^16, so 1 was the remaining hole; it now
gets the same diagnostic instead of aborting the parser.

Scalable vectors are unaffected: `<vscale x 1 x sN>` is a valid type and
stays legal through the `HasVScale` check.

AI assistance: drafted with AI help; reviewed and validated by me.

Added: 
    llvm/test/CodeGen/MIR/AArch64/parse-low-level-type-invalid11.mir

Modified: 
    llvm/lib/CodeGen/MIRParser/MIParser.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/MIRParser/MIParser.cpp b/llvm/lib/CodeGen/MIRParser/MIParser.cpp
index 4b951785e9c41..7b45d028efdd7 100644
--- a/llvm/lib/CodeGen/MIRParser/MIParser.cpp
+++ b/llvm/lib/CodeGen/MIRParser/MIParser.cpp
@@ -1965,8 +1965,9 @@ static bool verifyScalarSize(uint64_t Size) {
   return Size != 0 && isUInt<16>(Size);
 }
 
-static bool verifyVectorElementCount(uint64_t NumElts) {
-  return NumElts != 0 && isUInt<16>(NumElts);
+static bool verifyVectorElementCount(uint64_t NumElts, bool HasVScale) {
+  // A fixed-length vector needs at least two elements.
+  return NumElts != 0 && (HasVScale || NumElts != 1) && isUInt<16>(NumElts);
 }
 
 static bool verifyAddrSpace(uint64_t AddrSpace) {
@@ -2053,7 +2054,7 @@ bool MIParser::parseLowLevelType(StringRef::iterator Loc, LLT &Ty) {
   if (Token.isNot(MIToken::IntegerLiteral))
     return GetError();
   uint64_t NumElements = Token.integerValue().getZExtValue();
-  if (!verifyVectorElementCount(NumElements))
+  if (!verifyVectorElementCount(NumElements, HasVScale))
     return error("invalid number of vector elements");
 
   lex();

diff  --git a/llvm/test/CodeGen/MIR/AArch64/parse-low-level-type-invalid11.mir b/llvm/test/CodeGen/MIR/AArch64/parse-low-level-type-invalid11.mir
new file mode 100644
index 0000000000000..1a1e71ad28729
--- /dev/null
+++ b/llvm/test/CodeGen/MIR/AArch64/parse-low-level-type-invalid11.mir
@@ -0,0 +1,10 @@
+# RUN: not llc -mtriple=aarch64-- -run-pass=none -filetype=null %s 2>&1 | FileCheck %s
+# When a fixed-length low-level type vector has 1 element
+---
+name: test_vector_1_element
+body: |
+  bb.0:
+    liveins: $x0
+    ; CHECK: [[@LINE+1]]:11: invalid number of vector elements
+    %0:_(<1 x s64>) = G_IMPLICIT_DEF
+...