https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101649
Bug ID: 101649
Summary: -Wdouble-promotion warning emitted when floating point
literals are not actually promoted to doubles
Product: gcc
Version: 11.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: make_...@t-online.de
Target Milestone: ---
GCC emits a double promotion warning when using the literal 0.5 with a float.
For example
float func(float num) {
return num * 0.5;
}
warning: implicit conversion from 'float' to 'double' to match other operand of
binary expression [-Wdouble-promotion]
3 | return num * 0.5;
However, GCC does not actually use the double representation for this literal
(and others than can be represented equally in float as in double).
The assembler output for both "0.5" and "0.5f" is the same:
func(float):
push rbp
mov rbp, rsp
movss DWORD PTR [rbp-4], xmm0
movss xmm1, DWORD PTR [rbp-4]
movss xmm0, DWORD PTR .LC0[rip]
mulss xmm0, xmm1
pop rbp
ret
.LC0:
.long 1056964608
This warning is misleading and should not be emitted
