Index: llvm/trunk/lib/CodeGen/MachineInstr.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/MachineInstr.cpp
+++ llvm/trunk/lib/CodeGen/MachineInstr.cpp
@@ -447,6 +447,14 @@
       SmallString<16> Str;
       getFPImm()->getValueAPF().toString(Str);
       OS << "quad " << Str;
+    } else if (getFPImm()->getType()->isX86_FP80Ty()) {
+      APFloat APF = getFPImm()->getValueAPF();
+      OS << "x86_fp80 0xK";
+      APInt API = APF.bitcastToAPInt();
+      OS << format_hex_no_prefix(API.getHiBits(16).getZExtValue(), 4,
+                                 /*Upper=*/true);
+      OS << format_hex_no_prefix(API.getLoBits(64).getZExtValue(), 16,
+                                 /*Upper=*/true);
     } else {
       OS << getFPImm()->getValueAPF().convertToDouble();
     }
Index: llvm/trunk/test/CodeGen/X86/GlobalISel/x86_64-fallback.ll
===================================================================
--- llvm/trunk/test/CodeGen/X86/GlobalISel/x86_64-fallback.ll
+++ llvm/trunk/test/CodeGen/X86/GlobalISel/x86_64-fallback.ll
@@ -0,0 +1,18 @@
+; RUN: llc -O0 -mtriple=x86_64-linux-gnu -global-isel -global-isel-abort=2 -pass-remarks-missed='gisel*' -verify-machineinstrs %s -o %t.out 2> %t.err
+; RUN: FileCheck %s --check-prefix=FALLBACK-WITH-REPORT-OUT < %t.out
+; RUN: FileCheck %s --check-prefix=FALLBACK-WITH-REPORT-ERR < %t.err
+; This file checks that the fallback path to selection dag works.
+; The test is fragile in the sense that it must be updated to expose
+; something that fails with global-isel.
+; When we cannot produce a test case anymore, that means we can remove
+; the fallback path.
+
+; Check that we fallback on invoke translation failures.
+; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: unable to legalize instruction: %vreg1<def>(s80) = G_FCONSTANT x86_fp80 0xK4002A000000000000000
+; FALLBACK-WITH-REPORT-ERR: warning: Instruction selection used fallback path for test_x86_fp80_dump
+; FALLBACK-WITH-REPORT-OUT-LABEL: test_x86_fp80_dump:
+define void @test_x86_fp80_dump(x86_fp80* %ptr){
+  store x86_fp80 0xK4002A000000000000000, x86_fp80* %ptr, align 16
+  ret void
+}
+