Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -1065,7 +1065,8 @@
   }
   case Instruction::BitCast: {
     Type *SrcTy = I->getOperand(0)->getType();
-    if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) &&
+    if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy() ||
+         SrcTy->isFloatingPointTy()) &&
         // TODO: For now, not handling conversions like:
         // (bitcast i64 %x to <2 x i32>)
         !I->getType()->isVectorTy()) {
@@ -1372,6 +1373,12 @@
         KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
         break;
       }
+      case Intrinsic::fabs: {
+        Type *Ty = II->getType();
+        APInt SignBit = APInt::getSignBit(Ty->getScalarSizeInBits());
+        KnownZero |= APInt::getSplat(Ty->getPrimitiveSizeInBits(), SignBit);
+        break;
+      }
       case Intrinsic::x86_sse42_crc32_64_64:
         KnownZero |= APInt::getHighBitsSet(64, 32);
         break;
@@ -1431,8 +1438,9 @@
   unsigned BitWidth = KnownZero.getBitWidth();
 
   assert((V->getType()->isIntOrIntVectorTy() ||
+          V->getType()->isFPOrFPVectorTy() ||
           V->getType()->getScalarType()->isPointerTy()) &&
-         "Not integer or pointer type!");
+         "Not integer, floating point, or pointer type!");
   assert((DL.getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) &&
          (!V->getType()->isIntOrIntVectorTy() ||
           V->getType()->getScalarSizeInBits() == BitWidth) &&
Index: test/Transforms/InstCombine/fabs.ll
===================================================================
--- test/Transforms/InstCombine/fabs.ll
+++ test/Transforms/InstCombine/fabs.ll
@@ -41,6 +41,7 @@
 declare float @llvm.fabs.f32(float)
 declare double @llvm.fabs.f64(double)
 declare fp128 @llvm.fabs.f128(fp128)
+declare <4 x float> @llvm.fabs.v4f32(<4 x float>)
 
 define float @square_fabs_intrinsic_f32(float %x) {
   %mul = fmul float %x, %x
@@ -98,3 +99,27 @@
 ; CHECK-NEXT: ret float %sq
 }
 
+; A scalar fabs op makes the sign bit zero, so masking off all of the other bits means we can return zero.
+
+define i32 @fabs_value_tracking_f32(float %x) {
+  %call = call float @llvm.fabs.f32(float %x)
+  %bc = bitcast float %call to i32
+  %and = and i32 %bc, 2147483648
+  ret i32 %and
+
+; CHECK-LABEL: fabs_value_tracking_f32(
+; CHECK:       ret i32 0
+}
+
+; TODO: A vector fabs op makes the sign bits zero, so masking off all of the other bits means we can return zero.
+
+define <4 x i32> @fabs_value_tracking_v4f32(<4 x float> %x) {
+  %call = call <4 x float> @llvm.fabs.v4f32(<4 x float> %x)
+  %bc = bitcast <4 x float> %call to <4 x i32>
+  %and = and <4 x i32> %bc, <i32 2147483648, i32 2147483648, i32 2147483648, i32 2147483648>
+  ret <4 x i32> %and
+
+; CHECK-LABEL: fabs_value_tracking_v4f32(
+; CHECK:       ret <4 x i32> %and
+}
+