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* [gcc r14-1791] Avoid duplicate vector initializations during RTL expansion.
@ 2023-06-13 16:22 Roger Sayle
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From: Roger Sayle @ 2023-06-13 16:22 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:40eafcd83d6ee644ec48985fd5a9696921ea10e7
commit r14-1791-g40eafcd83d6ee644ec48985fd5a9696921ea10e7
Author: Roger Sayle <roger@nextmovesoftware.com>
Date: Tue Jun 13 17:20:31 2023 +0100
Avoid duplicate vector initializations during RTL expansion.
This middle-end patch avoids some redundant RTL for vector initialization
during RTL expansion. For the simple test case:
typedef __int128 v1ti __attribute__ ((__vector_size__ (16)));
__int128 key;
v1ti foo() {
return (v1ti){key};
}
the middle-end currently expands:
(set (reg:V1TI 85) (const_vector:V1TI [ (const_int 0) ]))
(set (reg:V1TI 85) (mem/c:V1TI (symbol_ref:DI ("key"))))
where we create a dead instruction that initializes the vector to zero,
immediately followed by a set of the entire vector. This patch skips
this zeroing instruction when the vector has only a single element.
It also updates the code to indicate when we've cleared the vector,
so that we don't need to initialize zero elements.
2023-06-13 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
* expr.cc (store_constructor) <case VECTOR_TYPE>: Don't bother
clearing vectors with only a single element. Set CLEARED if the
vector was initialized to zero.
Diff:
---
gcc/expr.cc | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/gcc/expr.cc b/gcc/expr.cc
index 868fa6e4cca..62cd8facf75 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -7531,8 +7531,11 @@ store_constructor (tree exp, rtx target, int cleared, poly_int64 size,
}
/* Inform later passes that the old value is dead. */
- if (!cleared && !vector && REG_P (target))
- emit_move_insn (target, CONST0_RTX (mode));
+ if (!cleared && !vector && REG_P (target) && maybe_gt (n_elts, 1u))
+ {
+ emit_move_insn (target, CONST0_RTX (mode));
+ cleared = 1;
+ }
if (MEM_P (target))
alias = MEM_ALIAS_SET (target);
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