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Unfinished work and ideas related to register scavenger.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35047 91177308-0d34-0410-b5e6-96231b3b80d8
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Evan Cheng 2007-03-09 19:34:51 +00:00
parent 87707b90b1
commit 2265b49193
1 changed files with 14 additions and 0 deletions
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lib/Target/ARM/README.txt
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@ -427,6 +427,7 @@ http://www.inf.u-szeged.hu/gcc-arm/
http://citeseer.ist.psu.edu/debus04linktime.html
//===---------------------------------------------------------------------===//
gcc generates smaller code for this function at -O2 or -Os:
void foo(signed char* p) {
@ -449,3 +450,16 @@ More seriously, there is a byte->word extend before
each comparison, where there should be only one, and the condition codes
are not remembered when the same two values are compared twice.
//===---------------------------------------------------------------------===//
More register scavenging work:
1. Use the register scavenger to track frame index materialized into registers
(those that do not fit in addressing modes) to allow reuse in the same BB.
2. Finish scavenging for Thumb.
3. We know some spills and restores are unnecessary. The issue is once live
intervals are merged, they are not never split. So every def is spilled
and every use requires a restore if the register allocator decides the
resulting live interval is not assigned a physical register. It may be
possible (with the help of the scavenger) to turn some spill / restore
pairs into register copies.