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Favors generating "not" over "xor -1". For example.

Browse Source 
unsigned test(unsigned a) {
  return ~a;
}
llvm used to generate:
movl    $4294967295, %eax
xorl    4(%esp), %eax

Now it generates:
movl      4(%esp), %eax
notl      %eax

It's 3 bytes shorter.

llvm-svn: 62661
This commit is contained in:
Evan Cheng 2009-01-21 02:09:05 +00:00
parent ba0f5e174f
commit 0ed6a9d7e0
2 changed files with 4 additions and 1 deletions
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3
lib/Target/X86/X86InstrInfo.td
View File

@ -1235,12 +1235,15 @@ let isTwoAddress = 0 in {
}
} // Defs = [EFLAGS]
// Match xor -1 to not. Favors these over a move imm + xor to save code size.
let AddedComplexity = 15 in {
def NOT8r : I<0xF6, MRM2r, (outs GR8 :$dst), (ins GR8 :$src), "not{b}\t$dst",
[(set GR8:$dst, (not GR8:$src))]>;
def NOT16r : I<0xF7, MRM2r, (outs GR16:$dst), (ins GR16:$src), "not{w}\t$dst",
[(set GR16:$dst, (not GR16:$src))]>, OpSize;
def NOT32r : I<0xF7, MRM2r, (outs GR32:$dst), (ins GR32:$src), "not{l}\t$dst",
[(set GR32:$dst, (not GR32:$src))]>;
}
let isTwoAddress = 0 in {
def NOT8m : I<0xF6, MRM2m, (outs), (ins i8mem :$dst), "not{b}\t$dst",
[(store (not (loadi8 addr:$dst)), addr:$dst)]>;

2
test/CodeGen/X86/xor_not.ll
View File

@ -1,4 +1,4 @@
; RUN: llvm-as < %s | llc -march=x86 | grep {not\[lwb\]} | count 3
; RUN: llvm-as < %s | llc -march=x86 | grep {not\[lwb\]} | count 4
; RUN: llvm-as < %s | llc -march=x86-64 | grep {not\[lwb\]} | count 4
define i32 @test(i32 %a, i32 %b) nounwind {
entry: