Remove the `x86_mmx` IR type. (#98505)

It is now translated to `<1 x i64>`, which allows the removal of a bunch
of special casing.

This _incompatibly_ changes the ABI of any LLVM IR function with
`x86_mmx` arguments or returns: instead of passing in mmx registers,
they will now be passed via integer registers. However, the real-world
incompatibility caused by this is expected to be minimal, because Clang
never uses the x86_mmx type -- it lowers `__m64` to either `<1 x i64>`
or `double`, depending on ABI.

This change does _not_ eliminate the SelectionDAG `MVT::x86mmx` type.
That type simply no longer corresponds to an IR type, and is used only
by MMX intrinsics and inline-asm operands.

Because SelectionDAGBuilder only knows how to generate the
operands/results of intrinsics based on the IR type, it thus now
generates the intrinsics with the type MVT::v1i64, instead of
MVT::x86mmx. We need to fix this before the DAG LegalizeTypes, and thus
have the X86 backend fix them up in DAGCombine. (This may be a
short-lived hack, if all the MMX intrinsics can be removed in upcoming
changes.)

Works towards issue #98272.

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/AsmParser/LLLexer.cpp b/llvm/lib/AsmParser/LLLexer.cpp
index 7d7fe19..c82e749 100644
--- a/llvm/lib/AsmParser/LLLexer.cpp
+++ b/llvm/lib/AsmParser/LLLexer.cpp
@@ -838,7 +838,8 @@ lltok::Kind LLLexer::LexIdentifier() {
   TYPEKEYWORD("ppc_fp128", Type::getPPC_FP128Ty(Context));
   TYPEKEYWORD("label",     Type::getLabelTy(Context));
   TYPEKEYWORD("metadata",  Type::getMetadataTy(Context));
-  TYPEKEYWORD("x86_mmx",   Type::getX86_MMXTy(Context));
+  TYPEKEYWORD("x86_mmx", llvm::FixedVectorType::get(
+                             llvm::IntegerType::get(Context, 64), 1));
   TYPEKEYWORD("x86_amx",   Type::getX86_AMXTy(Context));
   TYPEKEYWORD("token",     Type::getTokenTy(Context));
   TYPEKEYWORD("ptr",       PointerType::getUnqual(Context));