Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -3378,6 +3378,28 @@
       default:
         break;
       }
+    } else if (C->isNegative()) {
+      assert(!C->isNaN() && "Unexpected -NaN!");
+      // TODO: We can catch more cases by using a range check rather than
+      //       relying on CannotBeOrderedLessThanZero.
+      switch (Pred) {
+      case FCmpInst::FCMP_UGE:
+      case FCmpInst::FCMP_UGT:
+      case FCmpInst::FCMP_UNE:
+        // (X >= 0) implies (X > C) when (C < 0)
+        if (CannotBeOrderedLessThanZero(LHS, Q.TLI))
+          return getTrue(RetTy);
+        break;
+      case FCmpInst::FCMP_OEQ:
+      case FCmpInst::FCMP_OLE:
+      case FCmpInst::FCMP_OLT:
+        // (X >= 0) implies !(X < C) when (C < 0)
+        if (CannotBeOrderedLessThanZero(LHS, Q.TLI))
+          return getFalse(RetTy);
+        break;
+      default:
+        break;
+      }
     }
   }
 
Index: test/Transforms/InstCombine/cast-int-fcmp-eq-0.ll
===================================================================
--- test/Transforms/InstCombine/cast-int-fcmp-eq-0.ll
+++ test/Transforms/InstCombine/cast-int-fcmp-eq-0.ll
@@ -339,10 +339,9 @@
   ret i1 %cmp
 }
 
+; unsigned integer cannot possibly round to a negative
 ; CHECK-LABEL: @i32_cast_cmp_oeq_int_i32imin_uitofp(
-; CHECK: uitofp
-; CHECK: fcmp oeq
-; CHECK-NEXT: ret
+; CHECK-NEXT: ret i1 false
 define i1 @i32_cast_cmp_oeq_int_i32imin_uitofp(i32 %i) {
   %f = uitofp i32 %i to float
   %cmp = fcmp oeq float %f, 0xC1E0000000000000
@@ -379,10 +378,9 @@
   ret i1 %cmp
 }
 
+; unsigned integer cannot possibly round to a negative
 ; CHECK-LABEL: @i32_cast_cmp_oeq_int_negi32umax_uitofp(
-; CHECK: uitofp
-; CHECK: fcmp oeq
-; CHECK-NEXT: ret
+; CHECK-NEXT: ret i1 false
 define i1 @i32_cast_cmp_oeq_int_negi32umax_uitofp(i32 %i) {
   %f = uitofp i32 %i to float
   %cmp = fcmp oeq float %f, 0xC1F0000000000000
Index: test/Transforms/InstSimplify/floating-point-compare.ll
===================================================================
--- test/Transforms/InstSimplify/floating-point-compare.ll
+++ test/Transforms/InstSimplify/floating-point-compare.ll
@@ -276,9 +276,7 @@
 
 define i1 @known_positive_olt_with_negative_constant(double %a) {
 ; CHECK-LABEL: @known_positive_olt_with_negative_constant(
-; CHECK-NEXT:    [[CALL:%.*]] = call double @llvm.fabs.f64(double %a)
-; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt double [[CALL]], -1.000000e+00
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %call = call double @llvm.fabs.f64(double %a)
   %cmp = fcmp olt double %call, -1.0
@@ -287,9 +285,7 @@
 
 define <2 x i1> @known_positive_ole_with_negative_constant_splat_vec(<2 x double> %a) {
 ; CHECK-LABEL: @known_positive_ole_with_negative_constant_splat_vec(
-; CHECK-NEXT:    [[CALL:%.*]] = call <2 x double> @llvm.fabs.v2f64(<2 x double> %a)
-; CHECK-NEXT:    [[CMP:%.*]] = fcmp ole <2 x double> [[CALL]], <double -2.000000e+00, double -2.000000e+00>
-; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+; CHECK-NEXT:    ret <2 x i1> zeroinitializer
 ;
   %call = call <2 x double> @llvm.fabs.v2f64(<2 x double> %a)
   %cmp = fcmp ole <2 x double> %call, <double -2.0, double -2.0>
@@ -298,9 +294,7 @@
 
 define i1 @known_positive_ugt_with_negative_constant(double %a) {
 ; CHECK-LABEL: @known_positive_ugt_with_negative_constant(
-; CHECK-NEXT:    [[CALL:%.*]] = call double @llvm.fabs.f64(double %a)
-; CHECK-NEXT:    [[CMP:%.*]] = fcmp ugt double [[CALL]], -3.000000e+00
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %call = call double @llvm.fabs.f64(double %a)
   %cmp = fcmp ugt double %call, -3.0
@@ -309,15 +303,31 @@
 
 define <2 x i1> @known_positive_uge_with_negative_constant_splat_vec(<2 x double> %a) {
 ; CHECK-LABEL: @known_positive_uge_with_negative_constant_splat_vec(
-; CHECK-NEXT:    [[CALL:%.*]] = call <2 x double> @llvm.fabs.v2f64(<2 x double> %a)
-; CHECK-NEXT:    [[CMP:%.*]] = fcmp uge <2 x double> [[CALL]], <double -4.000000e+00, double -4.000000e+00>
-; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+; CHECK-NEXT:    ret <2 x i1> <i1 true, i1 true>
 ;
   %call = call <2 x double> @llvm.fabs.v2f64(<2 x double> %a)
   %cmp = fcmp uge <2 x double> %call, <double -4.0, double -4.0>
   ret <2 x i1> %cmp
 }
 
+define i1 @known_positive_oeq_with_negative_constant(double %a) {
+; CHECK-LABEL: @known_positive_oeq_with_negative_constant(
+; CHECK-NEXT:    ret i1 false
+;
+  %call = call double @llvm.fabs.f64(double %a)
+  %cmp = fcmp oeq double %call, -5.0
+  ret i1 %cmp
+}
+
+define <2 x i1> @known_positive_une_with_negative_constant_splat_vec(<2 x double> %a) {
+; CHECK-LABEL: @known_positive_une_with_negative_constant_splat_vec(
+; CHECK-NEXT:    ret <2 x i1> <i1 true, i1 true>
+;
+  %call = call <2 x double> @llvm.fabs.v2f64(<2 x double> %a)
+  %cmp = fcmp une <2 x double> %call, <double -6.0, double -6.0>
+  ret <2 x i1> %cmp
+}
+
 define i1 @nonans1(double %in1, double %in2) {
 ; CHECK-LABEL: @nonans1(
 ; CHECK-NEXT:    ret i1 false