diff options
| author | Dimitry Andric <dim@FreeBSD.org> | 2011-05-02 19:34:44 +0000 |
|---|---|---|
| committer | Dimitry Andric <dim@FreeBSD.org> | 2011-05-02 19:34:44 +0000 |
| commit | 6b943ff3a3f8617113ecbf611cf0f8957e4e19d2 (patch) | |
| tree | fc5f365fb9035b2d0c622bbf06c9bbe8627d7279 /lib/Target/ARM/README.txt | |
| parent | d0e4e96dc17a6c1c6de3340842c80f0e187ba349 (diff) | |
Notes
Diffstat (limited to 'lib/Target/ARM/README.txt')
| -rw-r--r-- | lib/Target/ARM/README.txt | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/lib/Target/ARM/README.txt b/lib/Target/ARM/README.txt index 9fc3fb92cb2c..8ba9a27e95c8 100644 --- a/lib/Target/ARM/README.txt +++ b/lib/Target/ARM/README.txt @@ -657,3 +657,27 @@ Note that both "tst" and "moveq" are redundant. //===---------------------------------------------------------------------===// +When loading immediate constants with movt/movw, if there are multiple +constants needed with the same low 16 bits, and those values are not live at +the same time, it would be possible to use a single movw instruction, followed +by multiple movt instructions to rewrite the high bits to different values. +For example: + + volatile store i32 -1, i32* inttoptr (i32 1342210076 to i32*), align 4, + !tbaa +!0 + volatile store i32 -1, i32* inttoptr (i32 1342341148 to i32*), align 4, + !tbaa +!0 + +is compiled and optimized to: + + movw r0, #32796 + mov.w r1, #-1 + movt r0, #20480 + str r1, [r0] + movw r0, #32796 @ <= this MOVW is not needed, value is there already + movt r0, #20482 + str r1, [r0] + +//===---------------------------------------------------------------------===// |