diff --git a/llvm/lib/Support/APFloat.cpp b/llvm/lib/Support/APFloat.cpp
--- a/llvm/lib/Support/APFloat.cpp
+++ b/llvm/lib/Support/APFloat.cpp
@@ -2191,7 +2191,7 @@
   if (shift < 0 && isFiniteNonZero()) {
     int exponentChange = significandMSB() + 1 - fromSemantics.precision;
     if (exponent + exponentChange < toSemantics.minExponent)
-      exponentChange = toSemantics.minExponent - exponent;
+      exponentChange = exponent - toSemantics.minExponent;
     if (exponentChange < shift)
       exponentChange = shift;
     if (exponentChange < 0) {
diff --git a/llvm/test/Transforms/InstCombine/fpcast.ll b/llvm/test/Transforms/InstCombine/fpcast.ll
--- a/llvm/test/Transforms/InstCombine/fpcast.ll
+++ b/llvm/test/Transforms/InstCombine/fpcast.ll
@@ -156,3 +156,55 @@
   ret half %t2
 }
 
+define float @fptrunc_double_to_float_rounding_to_zero0() {
+; CHECK-LABEL: @fptrunc_double_to_float_rounding_to_zero0(
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+  %trunc = fptrunc double 0x10000001 to float
+  ret float %trunc
+}
+
+define float @fptrunc_double_to_float_rounding_to_zero1() {
+; CHECK-LABEL: @fptrunc_double_to_float_rounding_to_zero1(
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+  %trunc = fptrunc double 0x11111111 to float
+  ret float %trunc
+}
+
+define float @fptrunc_double_to_float_rounding_to_zero2() {
+; CHECK-LABEL: @fptrunc_double_to_float_rounding_to_zero2(
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+  %trunc = fptrunc double 0x10000000 to float
+  ret float %trunc
+}
+
+define float @fptrunc_double_to_float_rounding_lower() {
+; CHECK-LABEL: @fptrunc_double_to_float_rounding_lower(
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+  %den_f = bitcast i32 1 to float
+  %den_d = fpext float %den_f to double
+  %div = fdiv double %den_d, 2.0
+  %bits = bitcast double %div to i64
+  %add = add i64 %bits, 0
+  %cast = bitcast i64 %add to double
+  %trunc = fptrunc double %cast to float
+  ret float %trunc
+}
+
+define float @fptrunc_double_to_float_rounding_upper() {
+; CHECK-LABEL: @fptrunc_double_to_float_rounding_upper(
+; CHECK-NEXT:    ret float 0x36A0000000000000
+;
+  %den_f = bitcast i32 1 to float
+  %den_d = fpext float %den_f to double
+  %div = fdiv double %den_d, 2.0
+  %bits = bitcast double %div to i64
+  %add = add i64 %bits, 1
+  %cast = bitcast i64 %add to double
+  %trunc = fptrunc double %cast to float
+  ret float %trunc
+}
+