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, 3 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index df75745..85ee231 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -564,16 +564,14 @@ Constant *FoldReinterpretLoadFromConst(Constant *C, Type *LoadTy,
     Type *MapTy = Type::getIntNTy(C->getContext(),
                                   DL.getTypeSizeInBits(LoadTy).getFixedValue());
     if (Constant *Res = FoldReinterpretLoadFromConst(C, MapTy, Offset, DL)) {
-      if (Res->isNullValue() && !LoadTy->isX86_MMXTy() &&
-          !LoadTy->isX86_AMXTy())
+      if (Res->isNullValue() && !LoadTy->isX86_AMXTy())
         // Materializing a zero can be done trivially without a bitcast
         return Constant::getNullValue(LoadTy);
       Type *CastTy = LoadTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(LoadTy) : LoadTy;
       Res = FoldBitCast(Res, CastTy, DL);
       if (LoadTy->isPtrOrPtrVectorTy()) {
         // For vector of pointer, we needed to first convert to a vector of integer, then do vector inttoptr
-        if (Res->isNullValue() && !LoadTy->isX86_MMXTy() &&
-            !LoadTy->isX86_AMXTy())
+        if (Res->isNullValue() && !LoadTy->isX86_AMXTy())
           return Constant::getNullValue(LoadTy);
         if (DL.isNonIntegralPointerType(LoadTy->getScalarType()))
           // Be careful not to replace a load of an addrspace value with an inttoptr here
@@ -764,7 +762,7 @@ Constant *llvm::ConstantFoldLoadFromUniformValue(Constant *C, Type *Ty,
   // uniform.
   if (!DL.typeSizeEqualsStoreSize(C->getType()))
     return nullptr;
-  if (C->isNullValue() && !Ty->isX86_MMXTy() && !Ty->isX86_AMXTy())
+  if (C->isNullValue() && !Ty->isX86_AMXTy())
     return Constant::getNullValue(Ty);
   if (C->isAllOnesValue() &&
       (Ty->isIntOrIntVectorTy() || Ty->isFPOrFPVectorTy()))