Add x86 tune to enable v2df vector reduction by paddpd.
The tune is disabled by default.
gcc/ChangeLog:
PR target/97147
* config/i386/i386.h (TARGET_V2DF_REDUCTION_PREFER_HADDPD):
New macro.
* config/i386/sse.md (*sse3_haddv2df3_low): Add
TARGET_V2DF_REDUCTION_PREFER_HADDPD.
(*sse3_hsubv2df3_low): Ditto.
* config/i386/x86-tune.def
(X86_TUNE_V2DF_REDUCTION_PREFER_HADDPD): New tune.
gcc/testsuite/ChangeLog:
PR target/97147
* gcc.target/i386/pr54400.c: Adjust testcase.
* gcc.target/i386/pr94147.c: New test.