Index: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp
@@ -3406,6 +3406,33 @@
   return nullptr;
 }
 
+/// An alternative way to test if a bit is set or not uses sgt/slt instead of
+/// eq/ne.
+static Value *simplifySelectWithFakeICmpEq(Value *CmpLHS, Value *TrueVal,
+                                           Value *FalseVal,
+                                           bool TrueWhenUnset) {
+  unsigned BitWidth = TrueVal->getType()->getScalarSizeInBits();
+  APInt MinSignedValue;
+  Value *X;
+  if (match(CmpLHS, m_Trunc(m_Value(X))) && (X == TrueVal || X == FalseVal)) {
+    // icmp slt (trunc X), 0  <--> icmp ne (and X, C), 0
+    // icmp sgt (trunc X), -1 <--> icmp eq (and X, C), 0
+    unsigned DestSize = CmpLHS->getType()->getScalarSizeInBits();
+    MinSignedValue = APInt::getSignedMinValue(DestSize).zext(BitWidth);
+  } else {
+    // icmp slt X, 0  <--> icmp ne (and X, C), 0
+    // icmp sgt X, -1 <--> icmp eq (and X, C), 0
+    X = CmpLHS;
+    MinSignedValue = APInt::getSignedMinValue(BitWidth);
+  }
+
+  if (Value *V = simplifySelectBitTest(TrueVal, FalseVal, X, &MinSignedValue,
+                                       TrueWhenUnset))
+    return V;
+
+  return nullptr;
+}
+
 /// Try to simplify a select instruction when its condition operand is an
 /// integer comparison.
 static Value *simplifySelectWithICmpCond(Value *CondVal, Value *TrueVal,
@@ -3418,9 +3445,6 @@
 
   // FIXME: This code is nearly duplicated in InstCombine. Using/refactoring
   // decomposeBitTestICmp() might help.
-  unsigned BitWidth =
-      Q.DL.getTypeSizeInBits(TrueVal->getType()->getScalarType());
-  APInt MinSignedValue = APInt::getSignBit(BitWidth);
   if (ICmpInst::isEquality(Pred) && match(CmpRHS, m_Zero())) {
     Value *X;
     const APInt *Y;
@@ -3429,12 +3453,14 @@
                                            Pred == ICmpInst::ICMP_EQ))
         return V;
   } else if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, m_Zero())) {
-    if (Value *V = simplifySelectBitTest(TrueVal, FalseVal, CmpLHS,
-                                         &MinSignedValue, false))
+    // Comparing signed-less-than 0 checks if the sign bit is set.
+    if (Value *V = simplifySelectWithFakeICmpEq(CmpLHS, TrueVal, FalseVal,
+                                                false))
       return V;
   } else if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_AllOnes())) {
-    if (Value *V = simplifySelectBitTest(TrueVal, FalseVal, CmpLHS,
-                                         &MinSignedValue, true))
+    // Comparing signed-greater-than -1 checks if the sign bit is not set.
+    if (Value *V = simplifySelectWithFakeICmpEq(CmpLHS, TrueVal, FalseVal,
+                                                true))
       return V;
   }
 
Index: llvm/trunk/test/Transforms/InstSimplify/select.ll
===================================================================
--- llvm/trunk/test/Transforms/InstSimplify/select.ll
+++ llvm/trunk/test/Transforms/InstSimplify/select.ll
@@ -228,11 +228,8 @@
 
 define i32 @select_icmp_trunc_8_ne_0_or_128(i32 %x) {
 ; CHECK-LABEL: @select_icmp_trunc_8_ne_0_or_128(
-; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i32 %x to i8
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[TRUNC]], -1
 ; CHECK-NEXT:    [[OR:%.*]] = or i32 %x, 128
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 [[OR]], i32 %x
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 [[OR]]
 ;
   %trunc = trunc i32 %x to i8
   %cmp = icmp sgt i8 %trunc, -1
@@ -243,11 +240,8 @@
 
 define i32 @select_icmp_trunc_8_ne_0_or_128_alt(i32 %x) {
 ; CHECK-LABEL: @select_icmp_trunc_8_ne_0_or_128_alt(
-; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i32 %x to i8
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[TRUNC]], 0
 ; CHECK-NEXT:    [[OR:%.*]] = or i32 %x, 128
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 %x, i32 [[OR]]
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 [[OR]]
 ;
   %trunc = trunc i32 %x to i8
   %cmp = icmp slt i8 %trunc, 0
@@ -258,11 +252,7 @@
 
 define i32 @select_icmp_trunc_8_eq_0_or_128(i32 %x) {
 ; CHECK-LABEL: @select_icmp_trunc_8_eq_0_or_128(
-; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i32 %x to i8
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[TRUNC]], 0
-; CHECK-NEXT:    [[OR:%.*]] = or i32 %x, 128
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 [[OR]], i32 %x
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 %x
 ;
   %trunc = trunc i32 %x to i8
   %cmp = icmp slt i8 %trunc, 0
@@ -273,11 +263,7 @@
 
 define i32 @select_icmp_trunc_8_eq_0_or_128_alt(i32 %x) {
 ; CHECK-LABEL: @select_icmp_trunc_8_eq_0_or_128_alt(
-; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i32 %x to i8
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[TRUNC]], -1
-; CHECK-NEXT:    [[OR:%.*]] = or i32 %x, 128
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 %x, i32 [[OR]]
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 %x
 ;
   %trunc = trunc i32 %x to i8
   %cmp = icmp sgt i8 %trunc, -1
@@ -288,11 +274,8 @@
 
 define i32 @select_icmp_trunc_8_eq_0_and_not_8(i32 %x) {
 ; CHECK-LABEL: @select_icmp_trunc_8_eq_0_and_not_8(
-; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i32 %x to i4
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i4 [[TRUNC]], -1
 ; CHECK-NEXT:    [[AND:%.*]] = and i32 %x, -9
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 %x, i32 [[AND]]
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 [[AND]]
 ;
   %trunc = trunc i32 %x to i4
   %cmp = icmp sgt i4 %trunc, -1
@@ -303,11 +286,8 @@
 
 define i32 @select_icmp_trunc_8_eq_0_and_not_8_alt(i32 %x) {
 ; CHECK-LABEL: @select_icmp_trunc_8_eq_0_and_not_8_alt(
-; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i32 %x to i4
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i4 [[TRUNC]], 0
 ; CHECK-NEXT:    [[AND:%.*]] = and i32 %x, -9
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 [[AND]], i32 %x
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 [[AND]]
 ;
   %trunc = trunc i32 %x to i4
   %cmp = icmp slt i4 %trunc, 0
@@ -318,11 +298,7 @@
 
 define i32 @select_icmp_trunc_8_ne_0_and_not_8(i32 %x) {
 ; CHECK-LABEL: @select_icmp_trunc_8_ne_0_and_not_8(
-; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i32 %x to i4
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i4 [[TRUNC]], 0
-; CHECK-NEXT:    [[AND:%.*]] = and i32 %x, -9
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 %x, i32 [[AND]]
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 %x
 ;
   %trunc = trunc i32 %x to i4
   %cmp = icmp slt i4 %trunc, 0
@@ -333,11 +309,7 @@
 
 define i32 @select_icmp_trunc_8_ne_0_and_not_8_alt(i32 %x) {
 ; CHECK-LABEL: @select_icmp_trunc_8_ne_0_and_not_8_alt(
-; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i32 %x to i4
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i4 [[TRUNC]], -1
-; CHECK-NEXT:    [[AND:%.*]] = and i32 %x, -9
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 [[AND]], i32 %x
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 %x
 ;
   %trunc = trunc i32 %x to i4
   %cmp = icmp sgt i4 %trunc, -1
@@ -361,11 +333,7 @@
 
 define <2 x i32> @select_icmp_trunc_8_ne_0_and_not_8_alt_vec(<2 x i32> %x) {
 ; CHECK-LABEL: @select_icmp_trunc_8_ne_0_and_not_8_alt_vec(
-; CHECK-NEXT:    [[TRUNC:%.*]] = trunc <2 x i32> %x to <2 x i4>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <2 x i4> [[TRUNC]], <i4 -1, i4 -1>
-; CHECK-NEXT:    [[AND:%.*]] = and <2 x i32> %x, <i32 -9, i32 -9>
-; CHECK-NEXT:    [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i32> [[AND]], <2 x i32> %x
-; CHECK-NEXT:    ret <2 x i32> [[SEL]]
+; CHECK-NEXT:    ret <2 x i32> %x
 ;
   %trunc = trunc <2 x i32> %x to <2 x i4>
   %cmp = icmp sgt <2 x i4> %trunc, <i4 -1, i4 -1>