Index: lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -4515,6 +4515,17 @@
       return new ICmpInst(Pred, X, ConstantInt::getNullValue(X->getType()));
   }
 
+  // Sign-bit checks can be optimized to true/false after unsigned
+  // floating-point casts:
+  // icmp slt (bitcast (uitofp X)),  0 --> false
+  // icmp sgt (bitcast (uitofp X)), -1 --> true
+  if (match(Op0, m_BitCast(m_UIToFP(m_Value(X))))) {
+    if (Pred == ICmpInst::ICMP_SLT && match(Op1, m_Zero()))
+      return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
+    if (Pred == ICmpInst::ICMP_SGT && match(Op1, m_AllOnes()))
+      return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
+  }
+
   // Test to see if the operands of the icmp are casted versions of other
   // values.  If the ptr->ptr cast can be stripped off both arguments, we do so
   // now.
Index: test/Transforms/InstCombine/cast-unsigned-icmp-cmp-0.ll
===================================================================
--- test/Transforms/InstCombine/cast-unsigned-icmp-cmp-0.ll
+++ test/Transforms/InstCombine/cast-unsigned-icmp-cmp-0.ll
@@ -12,10 +12,7 @@
 
 define i1 @i32_cast_cmp_slt_int_0_uitofp_float(i32 %i) {
 ; CHECK-LABEL: @i32_cast_cmp_slt_int_0_uitofp_float(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i32 [[I:%.*]] to float
-; CHECK-NEXT:    [[B:%.*]] = bitcast float [[F]] to i32
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[B]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %f = uitofp i32 %i to float
   %b = bitcast float %f to i32
@@ -38,10 +35,7 @@
 
 define i1 @i32_cast_cmp_sgt_int_m1_uitofp_float(i32 %i) {
 ; CHECK-LABEL: @i32_cast_cmp_sgt_int_m1_uitofp_float(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i32 [[I:%.*]] to float
-; CHECK-NEXT:    [[B:%.*]] = bitcast float [[F]] to i32
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[B]], -1
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %f = uitofp i32 %i to float
   %b = bitcast float %f to i32
@@ -51,10 +45,7 @@
 
 define <3 x i1> @i32_cast_cmp_sgt_int_m1_uitofp_float_vec(<3 x i32> %i) {
 ; CHECK-LABEL: @i32_cast_cmp_sgt_int_m1_uitofp_float_vec(
-; CHECK-NEXT:    [[F:%.*]] = uitofp <3 x i32> [[I:%.*]] to <3 x float>
-; CHECK-NEXT:    [[B:%.*]] = bitcast <3 x float> [[F]] to <3 x i32>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <3 x i32> [[B]], <i32 -1, i32 undef, i32 -1>
-; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+; CHECK-NEXT:    ret <3 x i1> <i1 true, i1 true, i1 true>
 ;
   %f = uitofp <3 x i32> %i to  <3 x float>
   %b = bitcast <3 x float> %f to <3 x i32>
@@ -64,10 +55,7 @@
 
 define i1 @i32_cast_cmp_slt_int_0_uitofp_double(i32 %i) {
 ; CHECK-LABEL: @i32_cast_cmp_slt_int_0_uitofp_double(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i32 [[I:%.*]] to double
-; CHECK-NEXT:    [[B:%.*]] = bitcast double [[F]] to i64
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i64 [[B]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %f = uitofp i32 %i to double
   %b = bitcast double %f to i64
@@ -90,10 +78,7 @@
 
 define i1 @i32_cast_cmp_sgt_int_m1_uitofp_double(i32 %i) {
 ; CHECK-LABEL: @i32_cast_cmp_sgt_int_m1_uitofp_double(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i32 [[I:%.*]] to double
-; CHECK-NEXT:    [[B:%.*]] = bitcast double [[F]] to i64
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i64 [[B]], -1
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %f = uitofp i32 %i to double
   %b = bitcast double %f to i64
@@ -103,10 +88,7 @@
 
 define <3 x i1> @i32_cast_cmp_sgt_int_m1_uitofp_double_vec(<3 x i32> %i) {
 ; CHECK-LABEL: @i32_cast_cmp_sgt_int_m1_uitofp_double_vec(
-; CHECK-NEXT:    [[F:%.*]] = uitofp <3 x i32> [[I:%.*]] to <3 x double>
-; CHECK-NEXT:    [[B:%.*]] = bitcast <3 x double> [[F]] to <3 x i64>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <3 x i64> [[B]], <i64 -1, i64 undef, i64 -1>
-; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+; CHECK-NEXT:    ret <3 x i1> <i1 true, i1 true, i1 true>
 ;
   %f = uitofp <3 x i32> %i to  <3 x double>
   %b = bitcast <3 x double> %f to <3 x i64>
@@ -116,10 +98,7 @@
 
 define i1 @i32_cast_cmp_slt_int_0_uitofp_half(i32 %i) {
 ; CHECK-LABEL: @i32_cast_cmp_slt_int_0_uitofp_half(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i32 [[I:%.*]] to half
-; CHECK-NEXT:    [[B:%.*]] = bitcast half [[F]] to i16
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i16 [[B]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %f = uitofp i32 %i to half
   %b = bitcast half %f to i16
@@ -142,10 +121,7 @@
 
 define i1 @i32_cast_cmp_sgt_int_m1_uitofp_half(i32 %i) {
 ; CHECK-LABEL: @i32_cast_cmp_sgt_int_m1_uitofp_half(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i32 [[I:%.*]] to half
-; CHECK-NEXT:    [[B:%.*]] = bitcast half [[F]] to i16
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i16 [[B]], -1
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %f = uitofp i32 %i to half
   %b = bitcast half %f to i16
@@ -155,10 +131,7 @@
 
 define <3 x i1> @i32_cast_cmp_sgt_int_m1_uitofp_half_vec(<3 x i32> %i) {
 ; CHECK-LABEL: @i32_cast_cmp_sgt_int_m1_uitofp_half_vec(
-; CHECK-NEXT:    [[F:%.*]] = uitofp <3 x i32> [[I:%.*]] to <3 x half>
-; CHECK-NEXT:    [[B:%.*]] = bitcast <3 x half> [[F]] to <3 x i16>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <3 x i16> [[B]], <i16 -1, i16 undef, i16 -1>
-; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+; CHECK-NEXT:    ret <3 x i1> <i1 true, i1 true, i1 true>
 ;
   %f = uitofp <3 x i32> %i to  <3 x half>
   %b = bitcast <3 x half> %f to <3 x i16>
@@ -168,10 +141,7 @@
 
 define i1 @i64_cast_cmp_slt_int_0_uitofp_float(i64 %i) {
 ; CHECK-LABEL: @i64_cast_cmp_slt_int_0_uitofp_float(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i64 [[I:%.*]] to float
-; CHECK-NEXT:    [[B:%.*]] = bitcast float [[F]] to i32
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[B]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %f = uitofp i64 %i to float
   %b = bitcast float %f to i32
@@ -194,10 +164,7 @@
 
 define i1 @i64_cast_cmp_sgt_int_m1_uitofp_float(i64 %i) {
 ; CHECK-LABEL: @i64_cast_cmp_sgt_int_m1_uitofp_float(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i64 [[I:%.*]] to float
-; CHECK-NEXT:    [[B:%.*]] = bitcast float [[F]] to i32
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[B]], -1
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %f = uitofp i64 %i to float
   %b = bitcast float %f to i32
@@ -207,10 +174,7 @@
 
 define <3 x i1> @i64_cast_cmp_sgt_int_m1_uitofp_float_vec(<3 x i64> %i) {
 ; CHECK-LABEL: @i64_cast_cmp_sgt_int_m1_uitofp_float_vec(
-; CHECK-NEXT:    [[F:%.*]] = uitofp <3 x i64> [[I:%.*]] to <3 x float>
-; CHECK-NEXT:    [[B:%.*]] = bitcast <3 x float> [[F]] to <3 x i32>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <3 x i32> [[B]], <i32 -1, i32 undef, i32 -1>
-; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+; CHECK-NEXT:    ret <3 x i1> <i1 true, i1 true, i1 true>
 ;
   %f = uitofp <3 x i64> %i to  <3 x float>
   %b = bitcast <3 x float> %f to <3 x i32>
@@ -220,10 +184,7 @@
 
 define i1 @i64_cast_cmp_slt_int_0_uitofp_double(i64 %i) {
 ; CHECK-LABEL: @i64_cast_cmp_slt_int_0_uitofp_double(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i64 [[I:%.*]] to double
-; CHECK-NEXT:    [[B:%.*]] = bitcast double [[F]] to i64
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i64 [[B]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %f = uitofp i64 %i to double
   %b = bitcast double %f to i64
@@ -246,10 +207,7 @@
 
 define i1 @i64_cast_cmp_sgt_int_m1_uitofp_double(i64 %i) {
 ; CHECK-LABEL: @i64_cast_cmp_sgt_int_m1_uitofp_double(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i64 [[I:%.*]] to double
-; CHECK-NEXT:    [[B:%.*]] = bitcast double [[F]] to i64
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i64 [[B]], -1
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %f = uitofp i64 %i to double
   %b = bitcast double %f to i64
@@ -259,10 +217,7 @@
 
 define <3 x i1> @i64_cast_cmp_sgt_int_m1_uitofp_double_vec(<3 x i64> %i) {
 ; CHECK-LABEL: @i64_cast_cmp_sgt_int_m1_uitofp_double_vec(
-; CHECK-NEXT:    [[F:%.*]] = uitofp <3 x i64> [[I:%.*]] to <3 x double>
-; CHECK-NEXT:    [[B:%.*]] = bitcast <3 x double> [[F]] to <3 x i64>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <3 x i64> [[B]], <i64 -1, i64 undef, i64 -1>
-; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+; CHECK-NEXT:    ret <3 x i1> <i1 true, i1 true, i1 true>
 ;
   %f = uitofp <3 x i64> %i to  <3 x double>
   %b = bitcast <3 x double> %f to <3 x i64>
@@ -272,10 +227,7 @@
 
 define i1 @i64_cast_cmp_slt_int_0_uitofp_half(i64 %i) {
 ; CHECK-LABEL: @i64_cast_cmp_slt_int_0_uitofp_half(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i64 [[I:%.*]] to half
-; CHECK-NEXT:    [[B:%.*]] = bitcast half [[F]] to i16
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i16 [[B]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %f = uitofp i64 %i to half
   %b = bitcast half %f to i16
@@ -298,10 +250,7 @@
 
 define i1 @i64_cast_cmp_sgt_int_m1_uitofp_half(i64 %i) {
 ; CHECK-LABEL: @i64_cast_cmp_sgt_int_m1_uitofp_half(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i64 [[I:%.*]] to half
-; CHECK-NEXT:    [[B:%.*]] = bitcast half [[F]] to i16
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i16 [[B]], -1
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %f = uitofp i64 %i to half
   %b = bitcast half %f to i16
@@ -311,10 +260,7 @@
 
 define <3 x i1> @i64_cast_cmp_sgt_int_m1_uitofp_half_vec(<3 x i64> %i) {
 ; CHECK-LABEL: @i64_cast_cmp_sgt_int_m1_uitofp_half_vec(
-; CHECK-NEXT:    [[F:%.*]] = uitofp <3 x i64> [[I:%.*]] to <3 x half>
-; CHECK-NEXT:    [[B:%.*]] = bitcast <3 x half> [[F]] to <3 x i16>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <3 x i16> [[B]], <i16 -1, i16 undef, i16 -1>
-; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+; CHECK-NEXT:    ret <3 x i1> <i1 true, i1 true, i1 true>
 ;
   %f = uitofp <3 x i64> %i to  <3 x half>
   %b = bitcast <3 x half> %f to <3 x i16>
@@ -324,10 +270,7 @@
 
 define i1 @i16_cast_cmp_slt_int_0_uitofp_float(i16 %i) {
 ; CHECK-LABEL: @i16_cast_cmp_slt_int_0_uitofp_float(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i16 [[I:%.*]] to float
-; CHECK-NEXT:    [[B:%.*]] = bitcast float [[F]] to i32
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[B]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %f = uitofp i16 %i to float
   %b = bitcast float %f to i32
@@ -350,10 +293,7 @@
 
 define i1 @i16_cast_cmp_sgt_int_m1_uitofp_float(i16 %i) {
 ; CHECK-LABEL: @i16_cast_cmp_sgt_int_m1_uitofp_float(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i16 [[I:%.*]] to float
-; CHECK-NEXT:    [[B:%.*]] = bitcast float [[F]] to i32
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[B]], -1
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %f = uitofp i16 %i to float
   %b = bitcast float %f to i32
@@ -363,10 +303,7 @@
 
 define <3 x i1> @i16_cast_cmp_sgt_int_m1_uitofp_float_vec(<3 x i16> %i) {
 ; CHECK-LABEL: @i16_cast_cmp_sgt_int_m1_uitofp_float_vec(
-; CHECK-NEXT:    [[F:%.*]] = uitofp <3 x i16> [[I:%.*]] to <3 x float>
-; CHECK-NEXT:    [[B:%.*]] = bitcast <3 x float> [[F]] to <3 x i32>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <3 x i32> [[B]], <i32 -1, i32 undef, i32 -1>
-; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+; CHECK-NEXT:    ret <3 x i1> <i1 true, i1 true, i1 true>
 ;
   %f = uitofp <3 x i16> %i to  <3 x float>
   %b = bitcast <3 x float> %f to <3 x i32>
@@ -376,10 +313,7 @@
 
 define i1 @i16_cast_cmp_slt_int_0_uitofp_double(i16 %i) {
 ; CHECK-LABEL: @i16_cast_cmp_slt_int_0_uitofp_double(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i16 [[I:%.*]] to double
-; CHECK-NEXT:    [[B:%.*]] = bitcast double [[F]] to i64
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i64 [[B]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %f = uitofp i16 %i to double
   %b = bitcast double %f to i64
@@ -402,10 +336,7 @@
 
 define i1 @i16_cast_cmp_sgt_int_m1_uitofp_double(i16 %i) {
 ; CHECK-LABEL: @i16_cast_cmp_sgt_int_m1_uitofp_double(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i16 [[I:%.*]] to double
-; CHECK-NEXT:    [[B:%.*]] = bitcast double [[F]] to i64
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i64 [[B]], -1
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %f = uitofp i16 %i to double
   %b = bitcast double %f to i64
@@ -415,10 +346,7 @@
 
 define <3 x i1> @i16_cast_cmp_sgt_int_m1_uitofp_double_vec(<3 x i16> %i) {
 ; CHECK-LABEL: @i16_cast_cmp_sgt_int_m1_uitofp_double_vec(
-; CHECK-NEXT:    [[F:%.*]] = uitofp <3 x i16> [[I:%.*]] to <3 x double>
-; CHECK-NEXT:    [[B:%.*]] = bitcast <3 x double> [[F]] to <3 x i64>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <3 x i64> [[B]], <i64 -1, i64 undef, i64 -1>
-; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+; CHECK-NEXT:    ret <3 x i1> <i1 true, i1 true, i1 true>
 ;
   %f = uitofp <3 x i16> %i to  <3 x double>
   %b = bitcast <3 x double> %f to <3 x i64>
@@ -428,10 +356,7 @@
 
 define i1 @i16_cast_cmp_slt_int_0_uitofp_half(i16 %i) {
 ; CHECK-LABEL: @i16_cast_cmp_slt_int_0_uitofp_half(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i16 [[I:%.*]] to half
-; CHECK-NEXT:    [[B:%.*]] = bitcast half [[F]] to i16
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i16 [[B]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %f = uitofp i16 %i to half
   %b = bitcast half %f to i16
@@ -454,10 +379,7 @@
 
 define i1 @i16_cast_cmp_sgt_int_m1_uitofp_half(i16 %i) {
 ; CHECK-LABEL: @i16_cast_cmp_sgt_int_m1_uitofp_half(
-; CHECK-NEXT:    [[F:%.*]] = uitofp i16 [[I:%.*]] to half
-; CHECK-NEXT:    [[B:%.*]] = bitcast half [[F]] to i16
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i16 [[B]], -1
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %f = uitofp i16 %i to half
   %b = bitcast half %f to i16
@@ -467,10 +389,7 @@
 
 define <3 x i1> @i16_cast_cmp_sgt_int_m1_uitofp_half_vec(<3 x i16> %i) {
 ; CHECK-LABEL: @i16_cast_cmp_sgt_int_m1_uitofp_half_vec(
-; CHECK-NEXT:    [[F:%.*]] = uitofp <3 x i16> [[I:%.*]] to <3 x half>
-; CHECK-NEXT:    [[B:%.*]] = bitcast <3 x half> [[F]] to <3 x i16>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <3 x i16> [[B]], <i16 -1, i16 undef, i16 -1>
-; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+; CHECK-NEXT:    ret <3 x i1> <i1 true, i1 true, i1 true>
 ;
   %f = uitofp <3 x i16> %i to  <3 x half>
   %b = bitcast <3 x half> %f to <3 x i16>