Add fused multiply-add instructions

This patch adds eight new primops that fuse a multiplication and an
addition or subtraction:

  - `{fmadd,fmsub,fnmadd,fnmsub}{Float,Double}#`

fmadd x y z is x * y + z, computed with a single rounding step.

This patch implements code generation for these primops in the following
backends:

  - X86, AArch64 and PowerPC NCG,
  - LLVM
  - C

WASM uses the C implementation. The primops are unsupported in the
JavaScript backend.

The following constant folding rules are also provided:

  - compute a * b + c when a, b, c are all literals,
  - x * y + 0 ==> x * y,
  - ±1 * y + z ==> z ± y and x * ±1 + z ==> z ± x.

NB: the constant folding rules incorrectly handle signed zero.
This is a known limitation with GHC's floating-point constant folding
rules (#21227), which we hope to resolve in the future.

1 files changed, 5 insertions, 0 deletions

diff --git a/testsuite/driver/cpu_features.py b/testsuite/driver/cpu_features.py
index 43500130db..f6c441d88f 100644
--- a/testsuite/driver/cpu_features.py
+++ b/testsuite/driver/cpu_features.py
@@ -10,6 +10,7 @@ SUPPORTED_CPU_FEATURES = {
     # x86:
     'sse', 'sse2', 'sse3', 'ssse3', 'sse4_1', 'sse4_2',
     'avx1', 'avx2',
+    'fma',
     'popcnt', 'bmi1', 'bmi2'
 }
 
@@ -46,6 +47,10 @@ def get_cpu_features():
         check_feature('avx2_0', 'avx2')
         return features
 
+    elif config.arch in [ 'powerpc', 'powerpc64' ]:
+        # Hardcode support for 'fma' on PowerPC
+        return [ 'fma' ]
+
     else:
         # TODO: Add {Open,Free}BSD support
         print('get_cpu_features: Lacking support for your platform')