llvm-6502/test/CodeGen/X86/select_const.ll at b8b3f6081f8dc409e7281e1597d8d94e50e4b028 - llvm-6502 - Applefritter: Git

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NAKAMURA Takumi e26874556b Reapply r165661, Patch by Shuxin Yang <shuxin.llvm@gmail.com>.

Original message:

The attached is the fix to radar://11663049. The optimization can be outlined by following rules:

   (select (x != c), e, c) -> select (x != c), e, x),
   (select (x == c), c, e) -> select (x == c), x, e)
where the <c> is an integer constant.

 The reason for this change is that : on x86, conditional-move-from-constant needs two instructions;
however, conditional-move-from-register need only one instruction.

  While the LowerSELECT() sounds to be the most convenient place for this optimization, it turns out to be a bad place. The reason is that by replacing the constant <c> with a symbolic value, it obscure some instruction-combining opportunities which would otherwise be very easy to spot. For that reason, I have to postpone the change to last instruction-combining phase.

  The change passes the test of "make check-all -C <build-root/test" and "make -C project/test-suite/SingleSource".

Original message since r165661:

My previous change has a bug: I negated the condition code of a CMOV, and go ahead creating a new CMOV using the *ORIGINAL* condition code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166017 91177308-0d34-0410-b5e6-96231b3b80d8

2012-10-16 06:28:34 +00:00

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 ; RUN: llc < %s -mtriple=x86_64-apple-darwin10 -mcpu=corei7 | FileCheck %s
 define i64 @test1(i64 %x) nounwind {
 entry:
   %cmp = icmp eq i64 %x, 2
   %add = add i64 %x, 1
   %retval.0 = select i1 %cmp, i64 2, i64 %add
   ret i64 %retval.0
 ; CHECK: test1:
 ; CHECK: leaq 1(%rdi), %rax
 ; CHECK: cmpq $2, %rdi
 ; CHECK: cmoveq %rdi, %rax
 ; CHECK: ret
 }