Index: llvm/trunk/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp
@@ -1358,6 +1358,12 @@
     if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
       switch (II->getIntrinsicID()) {
       default: break;
+      case Intrinsic::bswap:
+        computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL,
+                         Depth + 1, Q);
+        KnownZero |= KnownZero2.byteSwap();
+        KnownOne |= KnownOne2.byteSwap();
+        break;
       case Intrinsic::ctlz:
       case Intrinsic::cttz: {
         unsigned LowBits = Log2_32(BitWidth)+1;
Index: llvm/trunk/test/Transforms/InstCombine/bswap-known-bits.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/bswap-known-bits.ll
+++ llvm/trunk/test/Transforms/InstCombine/bswap-known-bits.ll
@@ -0,0 +1,47 @@
+; RUN: opt < %s -S -instcombine | FileCheck %s
+; Note: This is testing functionality in computeKnownBits.  I'd have rather
+; used instsimplify, but the bit test folding is apparently only in instcombine.
+
+declare i16 @llvm.bswap.i16(i16)
+declare i32 @llvm.bswap.i32(i32)
+
+define i1 @test1(i16 %arg) {
+; CHECK-LABEL: @test1
+; CHECK: ret i1 true
+  %a = or i16 %arg, 511
+  %b = call i16 @llvm.bswap.i16(i16 %a)
+  %and = and i16 %b, 256
+  %res = icmp eq i16 %and, 256
+  ret i1 %res
+}
+
+define i1 @test2(i16 %arg) {
+; CHECK-LABEL: @test2
+; CHECK: ret i1 true
+  %a = or i16 %arg, 1
+  %b = call i16 @llvm.bswap.i16(i16 %a)
+  %and = and i16 %b, 256
+  %res = icmp eq i16 %and, 256
+  ret i1 %res
+}
+
+
+define i1 @test3(i16 %arg) {
+; CHECK-LABEL: @test3
+; CHECK: ret i1 true
+  %a = or i16 %arg, 256
+  %b = call i16 @llvm.bswap.i16(i16 %a)
+  %and = and i16 %b, 1
+  %res = icmp eq i16 %and, 1
+  ret i1 %res
+}
+
+define i1 @test4(i32 %arg) {
+; CHECK-LABEL: @test4
+; CHECK: ret i1 true
+  %a = or i32 %arg, 2147483647  ; i32_MAX
+  %b = call i32 @llvm.bswap.i32(i32 %a)
+  %and = and i32 %b, 127
+  %res = icmp eq i32 %and, 127
+  ret i1 %res
+}
Index: llvm/trunk/test/Transforms/InstSimplify/bswap.ll
===================================================================
--- llvm/trunk/test/Transforms/InstSimplify/bswap.ll
+++ llvm/trunk/test/Transforms/InstSimplify/bswap.ll
@@ -0,0 +1,41 @@
+; RUN: opt < %s -S -instsimplify | FileCheck %s
+
+declare i16 @llvm.bswap.i16(i16)
+
+define i1 @test1(i16 %arg) {
+; CHECK-LABEL: @test1
+; CHECK: ret i1 false
+  %a = or i16 %arg, 1
+  %b = call i16 @llvm.bswap.i16(i16 %a)
+  %res = icmp eq i16 %b, 0
+  ret i1 %res
+}
+
+define i1 @test2(i16 %arg) {
+; CHECK-LABEL: @test2
+; CHECK: ret i1 false
+  %a = or i16 %arg, 1024
+  %b = call i16 @llvm.bswap.i16(i16 %a)
+  %res = icmp eq i16 %b, 0
+  ret i1 %res
+}
+
+define i1 @test3(i16 %arg) {
+; CHECK-LABEL: @test3
+; CHECK: ret i1 false
+  %a = and i16 %arg, 1
+  %b = call i16 @llvm.bswap.i16(i16 %a)
+  %and = and i16 %b, 1
+  %res = icmp eq i16 %and, 1
+  ret i1 %res
+}
+
+define i1 @test4(i16 %arg) {
+; CHECK-LABEL: @test4
+; CHECK: ret i1 false
+  %a = and i16 %arg, 511
+  %b = call i16 @llvm.bswap.i16(i16 %a)
+  %and = and i16 %b, 256
+  %res = icmp eq i16 %and, 1
+  ret i1 %res
+}