diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -9657,6 +9657,9 @@
   if (Constraint.size() == 1) {
     switch (Constraint[0]) {
     case 'r':
+      // TODO: Support fixed vectors up to XLen for P extension?
+      if (VT.isVector())
+        break;
       return std::make_pair(0U, &RISCV::GPRRegClass);
     case 'f':
       if (Subtarget.hasStdExtZfh() && VT == MVT::f16)
@@ -9669,17 +9672,15 @@
     default:
       break;
     }
-  } else {
-    if (Constraint == "vr") {
-      for (const auto *RC : {&RISCV::VRRegClass, &RISCV::VRM2RegClass,
-                             &RISCV::VRM4RegClass, &RISCV::VRM8RegClass}) {
-        if (TRI->isTypeLegalForClass(*RC, VT.SimpleTy))
-          return std::make_pair(0U, RC);
-      }
-    } else if (Constraint == "vm") {
-      if (TRI->isTypeLegalForClass(RISCV::VMV0RegClass, VT.SimpleTy))
-        return std::make_pair(0U, &RISCV::VMV0RegClass);
+  } else if (Constraint == "vr") {
+    for (const auto *RC : {&RISCV::VRRegClass, &RISCV::VRM2RegClass,
+                           &RISCV::VRM4RegClass, &RISCV::VRM8RegClass}) {
+      if (TRI->isTypeLegalForClass(*RC, VT.SimpleTy))
+        return std::make_pair(0U, RC);
     }
+  } else if (Constraint == "vm") {
+    if (TRI->isTypeLegalForClass(RISCV::VMV0RegClass, VT.SimpleTy))
+      return std::make_pair(0U, &RISCV::VMV0RegClass);
   }
 
   // Clang will correctly decode the usage of register name aliases into their
diff --git a/llvm/test/CodeGen/RISCV/inline-asm-invalid.ll b/llvm/test/CodeGen/RISCV/inline-asm-invalid.ll
--- a/llvm/test/CodeGen/RISCV/inline-asm-invalid.ll
+++ b/llvm/test/CodeGen/RISCV/inline-asm-invalid.ll
@@ -30,3 +30,15 @@
   tail call void asm "fadd.d fa0, fa0, $0", "f"(double 0.0)
   ret void
 }
+
+define void @constraint_r_fixed_vec() nounwind {
+; CHECK: error: couldn't allocate input reg for constraint 'r'
+  tail call void asm "add a0, a0, $0", "r"(<4 x i32> zeroinitializer)
+  ret void
+}
+
+define void @constraint_r_scalable_vec() nounwind {
+; CHECK: error: couldn't allocate input reg for constraint 'r'
+  tail call void asm "add a0, a0, $0", "r"(<vscale x 4 x i32> zeroinitializer)
+  ret void
+}