[AMDGPU] Fix crash for inline-asm inputs of type MVT::Other (#153401)

Author: ro-i

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -16476,6 +16476,11 @@ SITargetLowering::getRegForInlineAsmConstraint(const TargetRegisterInfo *TRI_,
 
   const TargetRegisterClass *RC = nullptr;
   if (Constraint.size() == 1) {
+    // Check if we cannot determine the bit size of the given value type.  This
+    // can happen, for example, in this situation where we have an empty struct
+    // (size 0): `call void asm "", "v"({} poison)`-
+    if (VT == MVT::Other)
+      return TargetLowering::getRegForInlineAsmConstraint(TRI, Constraint, VT);
     const unsigned BitWidth = VT.getSizeInBits();
     switch (Constraint[0]) {
     default:

llvm/test/CodeGen/AMDGPU/inlineasm-illegal-type.ll

@@ -18,6 +18,12 @@ define amdgpu_kernel void @v_input_output_i8() {
   ret void
 }
 
+; GCN: error: couldn't allocate input reg for constraint 'v'
+define amdgpu_kernel void @v_input_empty_struct() {
+  call void asm "", "v"({} poison)
+  ret void
+}
+
 ; SICI: error: couldn't allocate output register for constraint 's'
 ; SICI: error: couldn't allocate input reg for constraint 's'
 ; VI-NOT: error