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| author | Evan Cheng <evan.cheng@apple.com> | 2007-02-07 00:06:56 +0000 |
|---|---|---|
| committer | Evan Cheng <evan.cheng@apple.com> | 2007-02-07 00:06:56 +0000 |
| commit | 8e59ea998f1357768aa43cb00187e6c1c1a1cc7e (patch) | |
| tree | 9faddd5219816cb2829887a41040b7d1a7ad5f5d /lib/Target/ARM/README-Thumb.txt | |
| parent | c67da0cf13e2d671061449e8da4ffe102e5fc848 (diff) | |
| download | llvm-8e59ea998f1357768aa43cb00187e6c1c1a1cc7e.tar.gz llvm-8e59ea998f1357768aa43cb00187e6c1c1a1cc7e.tar.bz2 llvm-8e59ea998f1357768aa43cb00187e6c1c1a1cc7e.tar.xz | |
Spill / restore should avoid modifying the condition register.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33971 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/ARM/README-Thumb.txt')
| -rw-r--r-- | lib/Target/ARM/README-Thumb.txt | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/lib/Target/ARM/README-Thumb.txt b/lib/Target/ARM/README-Thumb.txt index 3bb8695b3a..6c2cb710ab 100644 --- a/lib/Target/ARM/README-Thumb.txt +++ b/lib/Target/ARM/README-Thumb.txt @@ -124,3 +124,20 @@ L12: .align 2 L11: .long 642 + +//===---------------------------------------------------------------------===// + +When spilling in thumb mode and the sp offset is too large to fit in the ldr / +str offset field, we load the offset from a constpool entry and add it to sp: + +ldr r2, LCPI +add r2, sp +ldr r2, [r2] + +These instructions preserve the condition code which is important if the spill +is between a cmp and a bcc instruction. However, we can use the (potentially) +cheaper sequnce if we know it's ok to clobber the condition register. + +add r2, sp, #255 * 4 +add r2, #132 +ldr r2, [r2, #7 * 4] |