Anastasia marked an inline comment as done.
Anastasia added inline comments.
================
Comment at: clang/test/CodeGenOpenCL/relaxed-fpmath.cl:21
+float fused_mad(float a, float b, float c) {
+ // NORMAL: @llvm.fmuladd.f32
+ // FAST: fmul fast float
----------------
Anastasia wrote:
> I don't find this behavior "NORMAL". I don't believe we should contract
> expressions by default in OpenCL...
I just found in table 38 of OpenCL C spec, last entry says:
> x * y + z
> Implemented either as a correctly rounded fma or as a multiply and an add
> both of which are correctly rounded.
In table 8 for `fma` it states:
> Returns the correctly rounded floating-point representation of the sum of c
> with the infinitely precise product of a and b. Rounding of intermediate
> products shall not occur.
When I check LLVM doecumentation for fmuladd it says:
> is equivalent to the expression a * b + c, except that it is unspecified
> whether rounding will be performed between the multiplication and addition
> steps. Fusion is not guaranteed, even if the target platform supports it. If
> a fused multiply-add is required, the corresponding llvm.fma intrinsic
> function should be used instead. This never sets errno, just as ‘llvm.fma.*’.
Does this mean that rounding of an intermediate product may occur and therefore
it is not safe to use it for OpenCL mode by default?
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D80416/new/
https://reviews.llvm.org/D80416
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