**
Revision
362921
by qshanz:
**[DAGCombine] Match a pattern where a wide type scalar value is stored by several narrow stores

This opportunity is found from spec 2017 557.xz_r. And it is used by the sha encrypt/decrypt. See sha-2/sha512.c

static void store64(u64 x, unsigned char* y)

{

for(int i = 0; i != 8; ++i)

y[i] = (x >> ((7-i) * 8)) & 255;

}

static u64 load64(const unsigned char* y)

{

u64 res = 0;

for(int i = 0; i != 8; ++i)

res |= (u64)(y[i]) << ((7-i) * 8);

return res;

}

The load64 has been implemented by https://reviews.llvm.org/D26149

This patch is trying to implement the store pattern.

Match a pattern where a wide type scalar value is stored by several narrow

stores. Fold it into a single store or a BSWAP and a store if the targets

supports it.

Assuming little endian target:

i8 *p = ...

i32 val = ...

p[0] = (val >> 0) & 0xFF;

p[1] = (val >> 8) & 0xFF;

p[2] = (val >> 16) & 0xFF;

p[3] = (val >> 24) & 0xFF;

>

*((i32)p) = val;

i8 *p = ...

i32 val = ...

p[0] = (val >> 24) & 0xFF;

p[1] = (val >> 16) & 0xFF;

p[2] = (val >> 8) & 0xFF;

p[3] = (val >> 0) & 0xFF;

>

*((i32)p) = BSWAP(val);

Differential Revision: https://reviews.llvm.org/D62897