X86: replace SUB with CMP if possible

This patch will optimize the following
        movq    %rdi, %rax
        subq    %rsi, %rax
        cmovsq  %rsi, %rdi
        movq    %rdi, %rax
to
        cmpq    %rsi, %rdi
        cmovsq  %rsi, %rdi
        movq    %rdi, %rax

Perform this optimization if the actual result of SUB is not used.

rdar: 11540023


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157755 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/CodeGen/PeepholeOptimizer.cpp b/lib/CodeGen/PeepholeOptimizer.cpp
index 81cf9011d1..d7d112f1d9 100644
--- a/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/lib/CodeGen/PeepholeOptimizer.cpp
@@ -472,6 +472,7 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
         if (SeenMoveImm)
           Changed |= foldImmediate(MI, MBB, ImmDefRegs, ImmDefMIs);
       }
+      Changed |= TII->OptimizeSubInstr(MI, MRI);
 
       First = false;
       PMII = MII;