Index: llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
===================================================================
--- llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
+++ llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
@@ -2289,6 +2289,7 @@
     const LLT s16 = LLT::scalar(16);
     const LLT s32 = LLT::scalar(32);
     const LLT s64 = LLT::scalar(64);
+    const LLT s128 = LLT::scalar(128);
     const LLT p0 = LLT::pointer(0, 64);
 
     const Register DefReg = I.getOperand(0).getReg();
@@ -2298,10 +2299,10 @@
 
     // FIXME: Redundant check, but even less readable when factored out.
     if (isFP) {
-      if (Ty != s32 && Ty != s64) {
+      if (Ty != s32 && Ty != s64 && Ty != s128) {
         LLVM_DEBUG(dbgs() << "Unable to materialize FP " << Ty
                           << " constant, expected: " << s32 << " or " << s64
-                          << '\n');
+                          << " or " << s128 << '\n');
         return false;
       }
 
@@ -2314,7 +2315,10 @@
 
       // The case when we have 0.0 is covered by tablegen. Reject it here so we
       // can be sure tablegen works correctly and isn't rescued by this code.
-      if (I.getOperand(1).getFPImm()->getValueAPF().isExactlyValue(0.0))
+      // 0.0 is not covered by tablegen for FP128. So we will handle this 
+      // scenario in the code here.
+      if (DefSize != 128 && 
+          I.getOperand(1).getFPImm()->getValueAPF().isExactlyValue(0.0))
         return false;
     } else {
       // s32 and s64 are covered by tablegen.
@@ -2341,15 +2345,17 @@
       // Either emit a FMOV, or emit a copy to emit a normal mov.
       const TargetRegisterClass &GPRRC =
           DefSize == 32 ? AArch64::GPR32RegClass : AArch64::GPR64RegClass;
-      const TargetRegisterClass &FPRRC =
-          DefSize == 32 ? AArch64::FPR32RegClass : AArch64::FPR64RegClass;
+      const TargetRegisterClass &FPRRC = 
+          DefSize == 32 ? AArch64::FPR32RegClass 
+                        : (DefSize == 64 ? AArch64::FPR64RegClass 
+                                         : AArch64::FPR128RegClass);
 
       // Can we use a FMOV instruction to represent the immediate?
       if (emitFMovForFConstant(I, MRI))
         return true;
 
       // For 64b values, emit a constant pool load instead.
-      if (DefSize == 64) {
+      if (DefSize == 64 || DefSize == 128) {
         auto *FPImm = I.getOperand(1).getFPImm();
         MachineIRBuilder MIB(I);
         auto *LoadMI = emitLoadFromConstantPool(FPImm, MIB);
Index: llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
===================================================================
--- llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
+++ llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
@@ -332,9 +332,9 @@
         const auto &Ty = Query.Types[0];
         if (HasFP16 && Ty == s16)
           return true;
-        return Ty == s32 || Ty == s64;
+        return Ty == s32 || Ty == s64 || Ty == s128;
       })
-      .clampScalar(0, MinFPScalar, s64);
+      .clampScalar(0, MinFPScalar, s128);
 
   getActionDefinitionsBuilder({G_ICMP, G_FCMP})
       .legalFor({{s32, s32},
Index: llvm/test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll
===================================================================
--- llvm/test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll
+++ llvm/test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll
@@ -64,13 +64,6 @@
 @_ZTIi = external global i8*
 declare i32 @__gxx_personality_v0(...)
 
-; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: unable to legalize instruction: %0:_(s128) = G_FCONSTANT fp128 0xL00000000000000004000000000000000
-; FALLBACK-WITH-REPORT-ERR: warning: Instruction selection used fallback path for test_quad_dump
-; FALLBACK-WITH-REPORT-OUT-LABEL: test_quad_dump:
-define fp128 @test_quad_dump() {
-  ret fp128 0xL00000000000000004000000000000000
-}
-
 ; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: unable to legalize instruction: %2:_(<2 x p0>) = G_INSERT_VECTOR_ELT %0:_, %{{[0-9]+}}:_(p0), %{{[0-9]+}}:_(s32) (in function: vector_of_pointers_insertelement)
 ; FALLBACK-WITH-REPORT-ERR: warning: Instruction selection used fallback path for vector_of_pointers_insertelement
 ; FALLBACK-WITH-REPORT-OUT-LABEL: vector_of_pointers_insertelement:
Index: llvm/test/CodeGen/AArch64/GlobalISel/legalize-fp128-fconstant.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AArch64/GlobalISel/legalize-fp128-fconstant.mir
@@ -0,0 +1,22 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -O0 -mtriple=aarch64 -run-pass=instruction-select -verify-machineinstrs %s -o - | FileCheck %s
+
+...
+---
+name:            fp128-fconstant
+alignment:       16
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    ; CHECK-LABEL: name: fp128-fconstant
+    ; CHECK: [[ADRP:%[0-9]+]]:gpr64common = ADRP target-flags(aarch64-page) %const.0
+    ; CHECK: [[LDRQui:%[0-9]+]]:fpr128 = LDRQui [[ADRP]], target-flags(aarch64-pageoff, aarch64-nc) %const.0
+    ; CHECK: $q0 = COPY [[LDRQui]]
+    ; CHECK: RET_ReallyLR implicit $q0
+    %0:fpr(s128) = G_FCONSTANT fp128 0xL00000000000000000000000000000000
+    $q0 = COPY %0:fpr(s128)
+    RET_ReallyLR implicit $q0
+...
+