In tree.def -
/* Minimum and maximum values. When used with floating point, if both
operands are zeros, or if either operand is NaN, then it is unspecified
which of the two operands is returned as the result. */
DEFTREECODE (MIN_EXPR, "min_expr", tcc_binary, 2)
DEFTREECODE (MAX_EXPR, "max_expr", tcc_binary, 2)
I see that the compiler cannot simplify an expression like
((a<b)?a:b) into a MIN_EXPR for FP data types without additional flags
(-ffinite-math-only -fno-signed zeros flags).
Q1: Its not clear to me what is the fundamental reason of the
"unspecified behaviour" of MIN_EXPR/MAX_EXPR in case of floating point
operands ?
(For the sake of discussing what I write hereafter, assume that
fminnm/fmaxnm
instructions offer better performance than fcsel/fcmp). So, two further
questions:
Q2. If one wants the compiler to generate fminnm/fmaxnm instructions, while
conforming with IEEE standard, the way to do that will be to use math
builtins fmin()/fmax(). Is this correct understanding?
Q3. Is there a way to make the compiler transform high-level language
floating
point construct like ((a<b)?a:b) to a fminnm/fmaxnm insn for aarch64
targets?
Thanks!
