Current implementation of division estimation isn't correct for some
cases like 1.0/0.0 (result is nan, not expected inf).
And this change exposes a potential infinite loop: we use
isConstOrConstSplatFP in combineRepeatedFPDivisors to look up if the
divisor is some constant. But it doesn't work after legalized on some
platforms. This patch restricts the method to act before LegalDAG.
Reviewed By: spatel
Differential Revision: https://reviews.llvm.org/D80542
Summary:
RCP has the accuracy limit. If FDIV fpmath require high accuracy rcp may not
meet the requirement. However, in DAG lowering, fpmath information gets lost,
and thus we may generate either inaccurate rcp related computation or slow code
for fdiv.
In patch implements fdiv optimizations in the AMDGPUCodeGenPrepare, which could
exactly know !fpmath.
FastUnsafeRcpLegal: We determine whether it is legal to use rcp based on
unsafe-fp-math, fast math flags, denormals and fpmath
accuracy request.
RCP Optimizations:
1/x -> rcp(x) when fast unsafe rcp is legal or fpmath >= 2.5ULP with
denormals flushed.
a/b -> a*rcp(b) when fast unsafe rcp is legal.
Use fdiv.fast:
a/b -> fdiv.fast(a, b) when RCP optimization is not performed and
fpmath >= 2.5ULP with denormals flushed.
1/x -> fdiv.fast(1,x) when RCP optimization is not performed and
fpmath >= 2.5ULP with denormals.
Reviewers:
arsenm
Differential Revision:
https://reviews.llvm.org/D71293
Current implementation of estimating divisions loses precision since it
estimates reciprocal first and does multiplication. This patch is to re-order
arithmetic operations in the last iteration in DAGCombiner to improve the
accuracy.
Reviewed By: Sanjay Patel, Jinsong Ji
Differential Revision: https://reviews.llvm.org/D66050
llvm-svn: 371713
Regardless of relaxation options such as -cl-fast-relaxed-math
we are producing rather long code for fdiv via amdgcn_fdiv_fast
intrinsic. This intrinsic is used to replace fdiv with 2.5ulp
metadata and does not handle denormals, thus believed to be fast.
An fdiv instruction can also have fast math flag either by itself
or together with fpmath metadata. Clang used with a relaxation flag
always produces both metadata and fast flag:
%div = fdiv fast float %v, %0, !fpmath !12!12 = !{float 2.500000e+00}
Current implementation ignores fast flag and favors metadata. An
instruction with just fast flag would be lowered to a fastest rcp +
mul, but that never happen on practice because of described mutual
clang and BE behavior.
This change allows an "fdiv fast" to be always lowered as rcp + mul.
Differential Revision: https://reviews.llvm.org/D34844
llvm-svn: 307308
Currently the default C calling convention functions are treated
the same as compute kernels. Make this explicit so the default
calling convention can be changed to a non-kernel.
Converted with perl -pi -e 's/define void/define amdgpu_kernel void/'
on the relevant test directories (and undoing in one place that actually
wanted a non-kernel).
llvm-svn: 298444
This switches to the workaround that HSA defaults to
for the mesa path.
This should be applied to the 4.0 branch.
Patch by Vedran Miletić <vedran@miletic.net>
llvm-svn: 292982
If 2.5 ulp is acceptable, denormals are not required, and
isn't a reciprocal which will already be handled, replace
with a faster fdiv.
Simplify the lowering tests by using per function
subtarget features.
llvm-svn: 276051
Qiu Chaofan