Index: lib/Target/Mips/MipsFastISel.cpp
===================================================================
--- lib/Target/Mips/MipsFastISel.cpp
+++ lib/Target/Mips/MipsFastISel.cpp
@@ -216,7 +216,7 @@
                         !Subtarget->inMicroMipsMode() && Subtarget->hasMips32();
     TargetSupported =
         ISASupported && TM.isPositionIndependent() && getABI().IsO32();
-    UnsupportedFPMode = Subtarget->isFP64bit();
+    UnsupportedFPMode = Subtarget->isFP64bit() || Subtarget->useSoftFloat();
   }
 
   unsigned fastMaterializeAlloca(const AllocaInst *AI) override;
@@ -1365,6 +1365,10 @@
       break;
 
     case MVT::f32:
+      if (UnsupportedFPMode) {
+        DEBUG(dbgs() << ".. .. gave up (UnsupportedFPMode)\n");
+        return false;
+      }
       if (NextFGR32 == FGR32ArgRegs.end()) {
         DEBUG(dbgs() << ".. .. gave up (ran out of FGR32 arguments)\n");
         return false;
@@ -1381,7 +1385,7 @@
 
     case MVT::f64:
       if (UnsupportedFPMode) {
-        DEBUG(dbgs() << ".. .. gave up (UnsupportedFPMode\n");
+        DEBUG(dbgs() << ".. .. gave up (UnsupportedFPMode)\n");
         return false;
       }
       if (NextAFGR64 == AFGR64ArgRegs.end()) {
Index: test/CodeGen/Mips/Fast-ISel/fast-isel-softfloat-lower-args.ll
===================================================================
--- /dev/null
+++ test/CodeGen/Mips/Fast-ISel/fast-isel-softfloat-lower-args.ll
@@ -0,0 +1,11 @@
+; RUN: not llc -march=mipsel -mcpu=mips32r2 -mattr=+soft-float \
+; RUN:         -O0 -fast-isel-abort=3 -relocation-model=pic < %s
+
+; Test that FastISel aborts instead of trying to lower arguments for soft-float.
+
+define void @__signbit(double %__x) {
+entry:
+  %__x.addr = alloca double, align 8
+  store double %__x, double* %__x.addr, align 8
+  ret void
+}