6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-01-09 10:31:14 +00:00
Code Issues Projects Releases Wiki Activity

Another missed memset in std::vector initialization.

Browse Source 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123116 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2011-01-09 11:29:57 +00:00
parent f78df5ebb8
commit 694d753b09
1 changed files with 19 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
lib/Target/README.txt
View File

@ -2230,3 +2230,22 @@ Then, the really painful one is the second memset, of the same memory, to the
same value.
//===---------------------------------------------------------------------===//
clang -O3 -fno-exceptions currently compiles this code:
struct S {
unsigned short m1, m2;
unsigned char m3, m4;
};
void f(int N) {
std::vector<S> v(N);
extern void sink(void*); sink(&v);
}
into poor code for zero-initializing 'v' when N is >0. The problem is that
S is only 6 bytes, but each element is 8 byte-aligned. We generate a loop and
4 stores on each iteration. If the struct were 8 bytes, this gets turned into
a memset.
//===---------------------------------------------------------------------===//