[X86] Add BLSI to isUseDefConvertible.

[craig.topper]

Summary

BLSI sets the C flag is the input is not zero. So if its followed
by a TEST of the input where only the Z flag is consumed, we can
replace it with the opposite check of the C flag.

We should be able to do the same for BLSMSK and BLSR, but the
naive test case for those is being optimized to a subo by
CodeGenPrepare.

[RKSimon]

LGTM

llvm/lib/Target/X86/X86InstrInfo.cpp

3374 ↗

(On Diff #205742)

Add TODO for BLSMSK and BLSR

llvm/trunk/lib/Target/X86/X86InstrInfo.cpp

case X86::TZCNT64rr:
     return X86::COND_B;
   case X86::BSF16rr:
   case X86::BSF32rr:
   case X86::BSF64rr:
   case X86::BSR16rr:
   case X86::BSR32rr:
   case X86::BSR64rr:
     return X86::COND_E;
+  case X86::BLSI32rr:
+  case X86::BLSI64rr:
+    return X86::COND_AE;
+  // TODO: BLSR, BLSMSK, and TBM instructions.
   }
 }
 
 /// Check if there exists an earlier instruction that
 /// operates on the same source operands and sets flags in the same way as
 /// Compare; remove Compare if possible.
 bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, unsigned SrcReg,
                                         unsigned SrcReg2, int CmpMask,

llvm/trunk/test/CodeGen/X86/bmi.ll

 ; X86-NEXT:    retl
 ; X86-NEXT:  .LBB50_1:
 ; X86-NEXT:    blsil %eax, %eax
 ; X86-NEXT:    retl
 ;
 ; X64-LABEL: blsi_cflag_32:
 ; X64:       # %bb.0:
 ; X64-NEXT:    blsil %edi, %eax
-; X64-NEXT:    testl %edi, %edi
-; X64-NEXT:    cmovel %esi, %eax
+; X64-NEXT:    cmovael %esi, %eax
 ; X64-NEXT:    retq
   %tobool = icmp eq i32 %x, 0
   %sub = sub nsw i32 0, %x
   %and = and i32 %sub, %x
   %cond = select i1 %tobool, i32 %y, i32 %and
   ret i32 %cond
 }
 

 ; X86-NEXT:  .LBB51_3:
 ; X86-NEXT:    popl %esi
 ; X86-NEXT:    popl %edi
 ; X86-NEXT:    retl
 ;
 ; X64-LABEL: blsi_cflag_64:
 ; X64:       # %bb.0:
 ; X64-NEXT:    blsiq %rdi, %rax
-; X64-NEXT:    testq %rdi, %rdi
-; X64-NEXT:    cmoveq %rsi, %rax
+; X64-NEXT:    cmovaeq %rsi, %rax
 ; X64-NEXT:    retq
   %tobool = icmp eq i64 %x, 0
   %sub = sub nsw i64 0, %x
   %and = and i64 %sub, %x
   %cond = select i1 %tobool, i64 %y, i64 %and
   ret i64 %cond
 }