https://bugs.llvm.org/show_bug.cgi?id=40550
Bug ID: 40550
Summary: missed optimization: dead stores in after memcpy
expansion
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Common Code Generator Code
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Consider the following code:
```
struct S {
char a[16];
};
void Swap(S& a, S& b) {
S tmp = a;
a = b;
b = tmp;
}
```
The generated code goes through the stack and generates 3
load/store pairs:
```
movups (%rdi), %xmm0
movaps %xmm0, -24(%rsp)
movups (%rsi), %xmm0
movups %xmm0, (%rdi)
movaps -24(%rsp), %xmm0
movups %xmm0, (%rsi)
```
With -combiner-global-alias-analysis, the combiner can avoid going through the
stack, but still generates a dead store:
```
movups (%rdi), %xmm0
movaps %xmm0, -24(%rsp)
movups (%rsi), %xmm1
movups %xmm1, (%rdi)
movups %xmm0, (%rsi)
```
The following code would be much better:
```
movups (%rdi), %xmm0
movups (%rsi), %xmm1
movups %xmm1, (%rdi)
movups %xmm0, (%rsi)
```
--
You are receiving this mail because:
You are on the CC list for the bug._______________________________________________
llvm-bugs mailing list
[email protected]
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
