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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34000 91177308-0d34-0410-b5e6-96231b3b80d8
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Evan Cheng 2007-02-07 09:22:15 +00:00
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9
lib/Target/ARM/README-Thumb.txt
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@ -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.