GCC modified for the FreeChainXenon project
fbc01748ba
Various bswapsi tests are failing for rv64. More importantly, we're generating
crappy code.
Let's take the first test from bswapsi-1.c as an example.
> typedef unsigned int uint32_t;
>
> #define __const_swab32(x) ((uint32_t)( \
> (((uint32_t)(x) & (uint32_t)0x000000ffUL) << 24) | \
> (((uint32_t)(x) & (uint32_t)0x0000ff00UL) << 8) | \
> (((uint32_t)(x) & (uint32_t)0x00ff0000UL) >> 8) | \
> (((uint32_t)(x) & (uint32_t)0xff000000UL) >> 24)))
>
> /* This byte swap implementation is used by the Linux kernel and the
> GNU C library. */
>
> uint32_t
> swap32_a (uint32_t in)
> {
> return __const_swab32 (in);
> }
>
>
>
We generate this for rv64gc_zba_zbb_zbs:
> srliw a1,a0,24
> slliw a5,a0,24
> slliw a3,a0,8
> li a2,16711680
> li a4,65536
> or a5,a5,a1
> and a3,a3,a2
> addi a4,a4,-256
> srliw a0,a0,8
> or a5,a5,a3
> and a0,a0,a4
> or a0,a5,a0
> retUrgh!
After this patch we generate:
> rev8 a0,a0
> srai a0,a0,32
> ret
Clearly better.
The stated rationale behind not exposing bswapsi2 for TARGET_64BIT is that the
RTL expanders already know how to widen a bswap, which is definitely true. But
it's the case that failure to expose a bswapsi will cause the 32bit bswap
optimizations in gimple store merging to not trigger. Thus we get crappy code.
To fix this we expose bswapsi on TARGET_64BIT. gimple-store-merging then
detects the 32bit bswap idioms and generates suitable __builtin calls. The
expander will "FAIL" expansion for TARGET_64BIT which forces the generic
expander code to synthesize the operation (we could synthesize in here, but
that'd result in duplicate code).
Tested on rv64gc_zba_zbb_zbs, fixes all the bswapsi failures in the testsuite
without any regressions.
gcc/
* config/riscv/bitmanip.md (bswapsi2): Expose for TARGET_64BIT.
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