try improving check_top_bit error message (#53166)

Fixes #30247

@staticfloat this was your issue, so what do you think of this? I think
the main problem was already solved (showing the wrong type), but I am
wondering if this wording is still clearer, since it tries to align it
with functions users might actually have encountered (trunc, convert,
signbit)

Author: vtjnash

base/boot.jl

@@ -744,12 +744,14 @@ function is_top_bit_set(x::Union{Int8,UInt8})
     eq_int(lshr_int(x, 7), trunc_int(typeof(x), 1))
 end
 
-#TODO delete this function (but see #48097):
+# n.b. This function exists for CUDA to overload to configure error behavior (see #48097)
 throw_inexacterror(args...) = throw(InexactError(args...))
 
-function check_top_bit(::Type{To}, x) where {To}
+function check_sign_bit(::Type{To}, x) where {To}
     @inline
-    is_top_bit_set(x) && throw_inexacterror(:check_top_bit, To, x)
+    # the top bit is the sign bit of x but "sign bit" sounds better in stacktraces
+    # n.b. if x is signed, then sizeof(x) === sizeof(To), otherwise sizeof(x) >= sizeof(To)
+    is_top_bit_set(x) && throw_inexacterror(sizeof(x) === sizeof(To) ? :convert : :trunc, To, x)
     x
 end
 
@@ -774,22 +776,22 @@ toInt8(x::Int16)      = checked_trunc_sint(Int8, x)
 toInt8(x::Int32)      = checked_trunc_sint(Int8, x)
 toInt8(x::Int64)      = checked_trunc_sint(Int8, x)
 toInt8(x::Int128)     = checked_trunc_sint(Int8, x)
-toInt8(x::UInt8)      = bitcast(Int8, check_top_bit(Int8, x))
-toInt8(x::UInt16)     = checked_trunc_sint(Int8, check_top_bit(Int8, x))
-toInt8(x::UInt32)     = checked_trunc_sint(Int8, check_top_bit(Int8, x))
-toInt8(x::UInt64)     = checked_trunc_sint(Int8, check_top_bit(Int8, x))
-toInt8(x::UInt128)    = checked_trunc_sint(Int8, check_top_bit(Int8, x))
+toInt8(x::UInt8)      = bitcast(Int8, check_sign_bit(Int8, x))
+toInt8(x::UInt16)     = checked_trunc_sint(Int8, check_sign_bit(Int8, x))
+toInt8(x::UInt32)     = checked_trunc_sint(Int8, check_sign_bit(Int8, x))
+toInt8(x::UInt64)     = checked_trunc_sint(Int8, check_sign_bit(Int8, x))
+toInt8(x::UInt128)    = checked_trunc_sint(Int8, check_sign_bit(Int8, x))
 toInt8(x::Bool)       = and_int(bitcast(Int8, x), Int8(1))
 toInt16(x::Int8)      = sext_int(Int16, x)
 toInt16(x::Int16)     = x
 toInt16(x::Int32)     = checked_trunc_sint(Int16, x)
 toInt16(x::Int64)     = checked_trunc_sint(Int16, x)
 toInt16(x::Int128)    = checked_trunc_sint(Int16, x)
 toInt16(x::UInt8)     = zext_int(Int16, x)
-toInt16(x::UInt16)    = bitcast(Int16, check_top_bit(Int16, x))
-toInt16(x::UInt32)    = checked_trunc_sint(Int16, check_top_bit(Int16, x))
-toInt16(x::UInt64)    = checked_trunc_sint(Int16, check_top_bit(Int16, x))
-toInt16(x::UInt128)   = checked_trunc_sint(Int16, check_top_bit(Int16, x))
+toInt16(x::UInt16)    = bitcast(Int16, check_sign_bit(Int16, x))
+toInt16(x::UInt32)    = checked_trunc_sint(Int16, check_sign_bit(Int16, x))
+toInt16(x::UInt64)    = checked_trunc_sint(Int16, check_sign_bit(Int16, x))
+toInt16(x::UInt128)   = checked_trunc_sint(Int16, check_sign_bit(Int16, x))
 toInt16(x::Bool)      = and_int(zext_int(Int16, x), Int16(1))
 toInt32(x::Int8)      = sext_int(Int32, x)
 toInt32(x::Int16)     = sext_int(Int32, x)
@@ -798,9 +800,9 @@ toInt32(x::Int64)     = checked_trunc_sint(Int32, x)
 toInt32(x::Int128)    = checked_trunc_sint(Int32, x)
 toInt32(x::UInt8)     = zext_int(Int32, x)
 toInt32(x::UInt16)    = zext_int(Int32, x)
-toInt32(x::UInt32)    = bitcast(Int32, check_top_bit(Int32, x))
-toInt32(x::UInt64)    = checked_trunc_sint(Int32, check_top_bit(Int32, x))
-toInt32(x::UInt128)   = checked_trunc_sint(Int32, check_top_bit(Int32, x))
+toInt32(x::UInt32)    = bitcast(Int32, check_sign_bit(Int32, x))
+toInt32(x::UInt64)    = checked_trunc_sint(Int32, check_sign_bit(Int32, x))
+toInt32(x::UInt128)   = checked_trunc_sint(Int32, check_sign_bit(Int32, x))
 toInt32(x::Bool)      = and_int(zext_int(Int32, x), Int32(1))
 toInt64(x::Int8)      = sext_int(Int64, x)
 toInt64(x::Int16)     = sext_int(Int64, x)
@@ -810,8 +812,8 @@ toInt64(x::Int128)    = checked_trunc_sint(Int64, x)
 toInt64(x::UInt8)     = zext_int(Int64, x)
 toInt64(x::UInt16)    = zext_int(Int64, x)
 toInt64(x::UInt32)    = zext_int(Int64, x)
-toInt64(x::UInt64)    = bitcast(Int64, check_top_bit(Int64, x))
-toInt64(x::UInt128)   = checked_trunc_sint(Int64, check_top_bit(Int64, x))
+toInt64(x::UInt64)    = bitcast(Int64, check_sign_bit(Int64, x))
+toInt64(x::UInt128)   = checked_trunc_sint(Int64, check_sign_bit(Int64, x))
 toInt64(x::Bool)      = and_int(zext_int(Int64, x), Int64(1))
 toInt128(x::Int8)     = sext_int(Int128, x)
 toInt128(x::Int16)    = sext_int(Int128, x)
@@ -822,9 +824,9 @@ toInt128(x::UInt8)    = zext_int(Int128, x)
 toInt128(x::UInt16)   = zext_int(Int128, x)
 toInt128(x::UInt32)   = zext_int(Int128, x)
 toInt128(x::UInt64)   = zext_int(Int128, x)
-toInt128(x::UInt128)  = bitcast(Int128, check_top_bit(Int128, x))
+toInt128(x::UInt128)  = bitcast(Int128, check_sign_bit(Int128, x))
 toInt128(x::Bool)     = and_int(zext_int(Int128, x), Int128(1))
-toUInt8(x::Int8)      = bitcast(UInt8, check_top_bit(UInt8, x))
+toUInt8(x::Int8)      = bitcast(UInt8, check_sign_bit(UInt8, x))
 toUInt8(x::Int16)     = checked_trunc_uint(UInt8, x)
 toUInt8(x::Int32)     = checked_trunc_uint(UInt8, x)
 toUInt8(x::Int64)     = checked_trunc_uint(UInt8, x)
@@ -835,8 +837,8 @@ toUInt8(x::UInt32)    = checked_trunc_uint(UInt8, x)
 toUInt8(x::UInt64)    = checked_trunc_uint(UInt8, x)
 toUInt8(x::UInt128)   = checked_trunc_uint(UInt8, x)
 toUInt8(x::Bool)      = and_int(bitcast(UInt8, x), UInt8(1))
-toUInt16(x::Int8)     = sext_int(UInt16, check_top_bit(UInt16, x))
-toUInt16(x::Int16)    = bitcast(UInt16, check_top_bit(UInt16, x))
+toUInt16(x::Int8)     = sext_int(UInt16, check_sign_bit(UInt16, x))
+toUInt16(x::Int16)    = bitcast(UInt16, check_sign_bit(UInt16, x))
 toUInt16(x::Int32)    = checked_trunc_uint(UInt16, x)
 toUInt16(x::Int64)    = checked_trunc_uint(UInt16, x)
 toUInt16(x::Int128)   = checked_trunc_uint(UInt16, x)
@@ -846,9 +848,9 @@ toUInt16(x::UInt32)   = checked_trunc_uint(UInt16, x)
 toUInt16(x::UInt64)   = checked_trunc_uint(UInt16, x)
 toUInt16(x::UInt128)  = checked_trunc_uint(UInt16, x)
 toUInt16(x::Bool)     = and_int(zext_int(UInt16, x), UInt16(1))
-toUInt32(x::Int8)     = sext_int(UInt32, check_top_bit(UInt32, x))
-toUInt32(x::Int16)    = sext_int(UInt32, check_top_bit(UInt32, x))
-toUInt32(x::Int32)    = bitcast(UInt32, check_top_bit(UInt32, x))
+toUInt32(x::Int8)     = sext_int(UInt32, check_sign_bit(UInt32, x))
+toUInt32(x::Int16)    = sext_int(UInt32, check_sign_bit(UInt32, x))
+toUInt32(x::Int32)    = bitcast(UInt32, check_sign_bit(UInt32, x))
 toUInt32(x::Int64)    = checked_trunc_uint(UInt32, x)
 toUInt32(x::Int128)   = checked_trunc_uint(UInt32, x)
 toUInt32(x::UInt8)    = zext_int(UInt32, x)
@@ -857,22 +859,22 @@ toUInt32(x::UInt32)   = x
 toUInt32(x::UInt64)   = checked_trunc_uint(UInt32, x)
 toUInt32(x::UInt128)  = checked_trunc_uint(UInt32, x)
 toUInt32(x::Bool)     = and_int(zext_int(UInt32, x), UInt32(1))
-toUInt64(x::Int8)     = sext_int(UInt64, check_top_bit(UInt64, x))
-toUInt64(x::Int16)    = sext_int(UInt64, check_top_bit(UInt64, x))
-toUInt64(x::Int32)    = sext_int(UInt64, check_top_bit(UInt64, x))
-toUInt64(x::Int64)    = bitcast(UInt64, check_top_bit(UInt64, x))
+toUInt64(x::Int8)     = sext_int(UInt64, check_sign_bit(UInt64, x))
+toUInt64(x::Int16)    = sext_int(UInt64, check_sign_bit(UInt64, x))
+toUInt64(x::Int32)    = sext_int(UInt64, check_sign_bit(UInt64, x))
+toUInt64(x::Int64)    = bitcast(UInt64, check_sign_bit(UInt64, x))
 toUInt64(x::Int128)   = checked_trunc_uint(UInt64, x)
 toUInt64(x::UInt8)    = zext_int(UInt64, x)
 toUInt64(x::UInt16)   = zext_int(UInt64, x)
 toUInt64(x::UInt32)   = zext_int(UInt64, x)
 toUInt64(x::UInt64)   = x
 toUInt64(x::UInt128)  = checked_trunc_uint(UInt64, x)
 toUInt64(x::Bool)     = and_int(zext_int(UInt64, x), UInt64(1))
-toUInt128(x::Int8)    = sext_int(UInt128, check_top_bit(UInt128, x))
-toUInt128(x::Int16)   = sext_int(UInt128, check_top_bit(UInt128, x))
-toUInt128(x::Int32)   = sext_int(UInt128, check_top_bit(UInt128, x))
-toUInt128(x::Int64)   = sext_int(UInt128, check_top_bit(UInt128, x))
-toUInt128(x::Int128)  = bitcast(UInt128, check_top_bit(UInt128, x))
+toUInt128(x::Int8)    = sext_int(UInt128, check_sign_bit(UInt128, x))
+toUInt128(x::Int16)   = sext_int(UInt128, check_sign_bit(UInt128, x))
+toUInt128(x::Int32)   = sext_int(UInt128, check_sign_bit(UInt128, x))
+toUInt128(x::Int64)   = sext_int(UInt128, check_sign_bit(UInt128, x))
+toUInt128(x::Int128)  = bitcast(UInt128, check_sign_bit(UInt128, x))
 toUInt128(x::UInt8)   = zext_int(UInt128, x)
 toUInt128(x::UInt16)  = zext_int(UInt128, x)
 toUInt128(x::UInt32)  = zext_int(UInt128, x)

src/common_symbols2.inc

@@ -8,7 +8,7 @@ jl_symbol("structdiff"),
 jl_symbol("UnitRange"),
 jl_symbol("unitrange_last"),
 jl_symbol("sizeof"),
-jl_symbol("check_top_bit"),
+jl_symbol("check_sign_bit"),
 jl_symbol("is_top_bit_set"),
 jl_symbol("data"),
 jl_symbol("kwerr"),