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ARM: peephole optimization to remove cmp instruction

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This patch will optimize the following cases:
  sub r1, r3 | sub r1, imm
  cmp r3, r1 or cmp r1, r3 | cmp r1, imm
  bge L1

TO
  subs r1, r3
  bge  L1 or ble L1

If the branch instruction can use flag from "sub", then we can replace
"sub" with "subs" and eliminate the "cmp" instruction.

rdar: 10734411


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@156599 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manman Ren
2012-05-11 01:30:47 +00:00
parent d4347e1af9
commit 247c5ab07c
3 changed files with 162 additions and 27 deletions
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9
lib/CodeGen/PeepholeOptimizer.cpp
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@ -31,6 +31,15 @@
// same flag that the "cmp" instruction sets and that "bz" uses, then we can
// eliminate the "cmp" instruction.
//
// Another instance, in this code:
//
// sub r1, r3 | sub r1, imm
// cmp r3, r1 or cmp r1, r3 | cmp r1, imm
// bge L1
//
// If the branch instruction can use flag from "sub", then we can replace
// "sub" with "subs" and eliminate the "cmp" instruction.
//
// - Optimize Bitcast pairs:
//
// v1 = bitcast v0