diff options
| -rw-r--r-- | lib/Target/ARM/README-Thumb.txt | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/lib/Target/ARM/README-Thumb.txt b/lib/Target/ARM/README-Thumb.txt index af02417d12..3818d83146 100644 --- a/lib/Target/ARM/README-Thumb.txt +++ b/lib/Target/ARM/README-Thumb.txt @@ -145,3 +145,12 @@ ldr r2, [r2, #7 * 4] This is especially bad when dynamic alloca is used. The all fixed size stack objects are referenced off the frame pointer with negative offsets. See oggenc for an example. + +//===---------------------------------------------------------------------===// + +We are reserving R3 as a scratch register under thumb mode. So if it is live in +to the function, we save / restore R3 to / from R12. Until register scavenging +is done, we should save R3 to a high callee saved reg at emitPrologue time +(when hasFP is true or stack size is large) and restore R3 from that register +instead. This allows us to at least get rid of the save to r12 everytime it is +used. |