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s390x: allow clang to emit fused multiply-adds (replicates gcc's default behavior) 

gcc's default setting for floating-point expression contraction is
"fast", which allows the compiler to emit fused multiply adds instead of
separate multiplies and adds (amongst others). Fused multiply-adds,
which assembly kernels typically apply, also bring a significant
performance advantage to the C implementation for matrix-matrix
multiplication on s390x. To enable that performance advantage for builds
with clang, add -ffp-contract=fast to the compiler options.

Signed-off-by: Marius Hillenbrand <mhillen@linux.ibm.com>
This commit is contained in:
Marius Hillenbrand 2020-09-01 15:09:32 +02:00
parent 87e5bbd887
commit 095f4e6964
1 changed files with 6 additions and 0 deletions
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6
Makefile.zarch
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@ -8,3 +8,9 @@ ifeq ($(CORE), Z14)
CCOMMON_OPT += -march=z14 -mzvector -O3
FCOMMON_OPT += -march=z14 -mzvector
endif
# Enable floating-point expression contraction for clang, since it is the
# default for gcc
ifeq ($(C_COMPILER), CLANG)
CCOMMON_OPT += -ffp-contract=fast
endif