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| author | Luc Van Oostenryck <luc.vanoostenryck@gmail.com> | 2018-07-18 16:06:28 +0200 |
|---|---|---|
| committer | Luc Van Oostenryck <luc.vanoostenryck@gmail.com> | 2018-07-25 18:47:09 +0200 |
| commit | 081b35e3a3d2ea50132b68816816966eceb6377f (patch) | |
| tree | 71dfc77fc808f2cf84a5fee15182a36f82ade389 | |
| parent | 52579227fdc1978bb12be250ab063deaeccbde0f (diff) | |
| download | sparse-dev-081b35e3a3d2ea50132b68816816966eceb6377f.tar.gz | |
shift: simplify ASR(ZEXT(X, N), C)
After an OP_ZEXT, it is guaranteed that the sign bit is zero.
So, an arithmetic right-shift following an OP_ZEXT gives the
same result as an logical right-shift which is simpler to handle
and further optimize.
So, when preceded by an OP_ZEXT, replace OP_ASR by OP_LSR.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
| -rw-r--r-- | simplify.c | 10 | ||||
| -rw-r--r-- | validation/optim/zext-asr.c | 13 |
2 files changed, 23 insertions, 0 deletions
@@ -606,6 +606,16 @@ static int simplify_shift(struct instruction *insn, pseudo_t pseudo, long long v else if (value >= size) value = size - 1; goto new_value; + + case OP_ZEXT: + // transform: + // zext.N %t <- (O) %a + // asr.N %r <- %t, C + // into + // zext.N %t <- (O) %a + // lsr.N %r <- %t, C + insn->opcode = OP_LSR; + return REPEAT_CSE; } break; case OP_LSR: diff --git a/validation/optim/zext-asr.c b/validation/optim/zext-asr.c new file mode 100644 index 00000000..5f235ad8 --- /dev/null +++ b/validation/optim/zext-asr.c @@ -0,0 +1,13 @@ +unsigned short foo(unsigned short a) +{ + return a >> 16; +} + +/* + * check-name: zext-asr + * check-command: test-linearize -Wno-decl $file + * + * check-output-ignore + * check-output-contains: ret\\..*\\$0 + * check-output-excludes: asr\\. + */ |