Re-enable the CMN instruction.

We turned off the CMN instruction because it had semantics which we weren't
getting correct. If we are comparing with an immediate, then it's okay to use
the CMN instruction.
<rdar://problem/7569620>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158302 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 144 insertions, 69 deletions

diff --git a/lib/Target/ARM/ARMFastISel.cpp b/lib/Target/ARM/ARMFastISel.cpp
index b353992b3b..e5d5157dd5 100644
--- a/lib/Target/ARM/ARMFastISel.cpp
+++ b/lib/Target/ARM/ARMFastISel.cpp
@@ -1420,12 +1420,12 @@ bool ARMFastISel::ARMEmitCmp(const Value *Src1Value, const Value *Src2Value,
         if (!UseImm)
           CmpOpc = ARM::t2CMPrr;
         else
-          CmpOpc = isNegativeImm ? ARM::t2CMNzri : ARM::t2CMPri;
+          CmpOpc = isNegativeImm ? ARM::t2CMNri : ARM::t2CMPri;
       } else {
         if (!UseImm)
           CmpOpc = ARM::CMPrr;
         else
-          CmpOpc = isNegativeImm ? ARM::CMNzri : ARM::CMPri;
+          CmpOpc = isNegativeImm ? ARM::CMNri : ARM::CMPri;
       }
       break;
   }
diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 8c71021c6c..c48fa763b4 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -895,6 +895,7 @@ const char *ARMTargetLowering::getTargetNodeName(unsigned Opcode) const {
   case ARMISD::RET_FLAG:      return "ARMISD::RET_FLAG";
   case ARMISD::PIC_ADD:       return "ARMISD::PIC_ADD";
   case ARMISD::CMP:           return "ARMISD::CMP";
+  case ARMISD::CMN:           return "ARMISD::CMN";
   case ARMISD::CMPZ:          return "ARMISD::CMPZ";
   case ARMISD::CMPFP:         return "ARMISD::CMPFP";
   case ARMISD::CMPFPw0:       return "ARMISD::CMPFPw0";
diff --git a/lib/Target/ARM/ARMISelLowering.h b/lib/Target/ARM/ARMISelLowering.h
index a113878978..7ad48b9b53 100644
--- a/lib/Target/ARM/ARMISelLowering.h
+++ b/lib/Target/ARM/ARMISelLowering.h
@@ -56,6 +56,7 @@ namespace llvm {
       PIC_ADD,      // Add with a PC operand and a PIC label.
 
       CMP,          // ARM compare instructions.
+      CMN,          // ARM CMN instructions.
       CMPZ,         // ARM compare that sets only Z flag.
       CMPFP,        // ARM VFP compare instruction, sets FPSCR.
       CMPFPw0,      // ARM VFP compare against zero instruction, sets FPSCR.
diff --git a/lib/Target/ARM/ARMInstrInfo.td b/lib/Target/ARM/ARMInstrInfo.td
index 8ffb5752c8..50ae826a38 100644
--- a/lib/Target/ARM/ARMInstrInfo.td
+++ b/lib/Target/ARM/ARMInstrInfo.td
@@ -128,6 +128,9 @@ def ARMBcci64        : SDNode<"ARMISD::BCC_i64", SDT_ARMBCC_i64,
 def ARMcmp           : SDNode<"ARMISD::CMP", SDT_ARMCmp,
                               [SDNPOutGlue]>;
 
+def ARMcmn           : SDNode<"ARMISD::CMN", SDT_ARMCmp,
+                              [SDNPOutGlue]>;
+
 def ARMcmpZ          : SDNode<"ARMISD::CMPZ", SDT_ARMCmp,
                               [SDNPOutGlue, SDNPCommutative]>;
 
@@ -3842,49 +3845,85 @@ def : ARMPat<(ARMcmpZ GPR:$src, so_reg_imm:$rhs),
 def : ARMPat<(ARMcmpZ GPR:$src, so_reg_reg:$rhs),
              (CMPrsr   GPR:$src, so_reg_reg:$rhs)>;
 
-// FIXME: We have to be careful when using the CMN instruction and comparison
-// with 0. One would expect these two pieces of code should give identical
-// results:
-//
-//   rsbs r1, r1, 0
-//   cmp  r0, r1
-//   mov  r0, #0
-//   it   ls
-//   mov  r0, #1
-//
-// and:
-//
-//   cmn  r0, r1
-//   mov  r0, #0
-//   it   ls
-//   mov  r0, #1
-//
-// However, the CMN gives the *opposite* result when r1 is 0. This is because
-// the carry flag is set in the CMP case but not in the CMN case. In short, the
-// CMP instruction doesn't perform a truncate of the (logical) NOT of 0 plus the
-// value of r0 and the carry bit (because the "carry bit" parameter to
-// AddWithCarry is defined as 1 in this case, the carry flag will always be set
-// when r0 >= 0). The CMN instruction doesn't perform a NOT of 0 so there is
-// never a "carry" when this AddWithCarry is performed (because the "carry bit"
-// parameter to AddWithCarry is defined as 0).
-//
-// When x is 0 and unsigned:
-//
-//    x = 0
-//   ~x = 0xFFFF FFFF
-//   ~x + 1 = 0x1 0000 0000
-//   (-x = 0) != (0x1 0000 0000 = ~x + 1)
-//
-// Therefore, we should disable CMN when comparing against zero, until we can
-// limit when the CMN instruction is used (when we know that the RHS is not 0 or
-// when it's a comparison which doesn't look at the 'carry' flag).
-//
-// (See the ARM docs for the "AddWithCarry" pseudo-code.)
-//
-// This is related to <rdar://problem/7569620>.
-//
-//defm CMN  : AI1_cmp_irs<0b1011, "cmn",
-//                        BinOpFrag<(ARMcmp node:$LHS,(ineg node:$RHS))>>;
+// CMN register-integer
+let isCompare = 1, Defs = [CPSR] in {
+def CMNri : AI1<0b1011, (outs), (ins GPR:$Rn, so_imm:$imm), DPFrm, IIC_iCMPi,
+                "cmn", "\t$Rn, $imm",
+                [(ARMcmn GPR:$Rn, so_imm:$imm)]> {
+  bits<4> Rn;
+  bits<12> imm;
+  let Inst{25} = 1;
+  let Inst{20} = 1;
+  let Inst{19-16} = Rn;
+  let Inst{15-12} = 0b0000;
+  let Inst{11-0} = imm;
+
+  let Unpredictable{15-12} = 0b1111;
+}
+
+// CMN register-register/shift
+def CMNzrr : AI1<0b1011, (outs), (ins GPR:$Rn, GPR:$Rm), DPFrm, IIC_iCMPr,
+                 "cmn", "\t$Rn, $Rm",
+                 [(BinOpFrag<(ARMcmpZ node:$LHS,(ineg node:$RHS))>
+                   GPR:$Rn, GPR:$Rm)]> {
+  bits<4> Rn;
+  bits<4> Rm;
+  let isCommutable = 1;
+  let Inst{25} = 0;
+  let Inst{20} = 1;
+  let Inst{19-16} = Rn;
+  let Inst{15-12} = 0b0000;
+  let Inst{11-4} = 0b00000000;
+  let Inst{3-0} = Rm;
+
+  let Unpredictable{15-12} = 0b1111;
+}
+
+def CMNzrsi : AI1<0b1011, (outs),
+                  (ins GPR:$Rn, so_reg_imm:$shift), DPSoRegImmFrm, IIC_iCMPsr,
+                  "cmn", "\t$Rn, $shift",
+                  [(BinOpFrag<(ARMcmpZ node:$LHS,(ineg node:$RHS))>
+                    GPR:$Rn, so_reg_imm:$shift)]> {
+  bits<4> Rn;
+  bits<12> shift;
+  let Inst{25} = 0;
+  let Inst{20} = 1;
+  let Inst{19-16} = Rn;
+  let Inst{15-12} = 0b0000;
+  let Inst{11-5} = shift{11-5};
+  let Inst{4} = 0;
+  let Inst{3-0} = shift{3-0};
+
+  let Unpredictable{15-12} = 0b1111;
+}
+
+def CMNzrsr : AI1<0b1011, (outs),
+                  (ins GPRnopc:$Rn, so_reg_reg:$shift), DPSoRegRegFrm, IIC_iCMPsr,
+                  "cmn", "\t$Rn, $shift",
+                  [(BinOpFrag<(ARMcmpZ node:$LHS,(ineg node:$RHS))>
+                    GPRnopc:$Rn, so_reg_reg:$shift)]> {
+  bits<4> Rn;
+  bits<12> shift;
+  let Inst{25} = 0;
+  let Inst{20} = 1;
+  let Inst{19-16} = Rn;
+  let Inst{15-12} = 0b0000;
+  let Inst{11-8} = shift{11-8};
+  let Inst{7} = 0;
+  let Inst{6-5} = shift{6-5};
+  let Inst{4} = 1;
+  let Inst{3-0} = shift{3-0};
+
+  let Unpredictable{15-12} = 0b1111;
+}
+
+}
+
+def : ARMPat<(ARMcmp  GPR:$src, so_imm_neg:$imm),
+             (CMNri   GPR:$src, so_imm_neg:$imm)>;
+
+def : ARMPat<(ARMcmpZ GPR:$src, so_imm_neg:$imm),
+             (CMNri   GPR:$src, so_imm_neg:$imm)>;
 
 // Note that TST/TEQ don't set all the same flags that CMP does!
 defm TST  : AI1_cmp_irs<0b1000, "tst",
@@ -3894,16 +3933,6 @@ defm TEQ  : AI1_cmp_irs<0b1001, "teq",
                         IIC_iTSTi, IIC_iTSTr, IIC_iTSTsr,
                       BinOpFrag<(ARMcmpZ (xor_su node:$LHS, node:$RHS), 0)>, 1>;
 
-defm CMNz  : AI1_cmp_irs<0b1011, "cmn",
-                         IIC_iCMPi, IIC_iCMPr, IIC_iCMPsr,
-                         BinOpFrag<(ARMcmpZ node:$LHS,(ineg node:$RHS))>>;
-
-//def : ARMPat<(ARMcmp GPR:$src, so_imm_neg:$imm),
-//             (CMNri  GPR:$src, so_imm_neg:$imm)>;
-
-def : ARMPat<(ARMcmpZ GPR:$src, so_imm_neg:$imm),
-             (CMNzri  GPR:$src, so_imm_neg:$imm)>;
-
 // Pseudo i64 compares for some floating point compares.
 let usesCustomInserter = 1, isBranch = 1, isTerminator = 1,
     Defs = [CPSR] in {
@@ -5052,7 +5081,7 @@ def : ARMInstAlias<"add${s}${p} $Rd, $imm",
                  (SUBri GPR:$Rd, GPR:$Rd, so_imm_neg:$imm, pred:$p, cc_out:$s)>;
 // Same for CMP <--> CMN via so_imm_neg
 def : ARMInstAlias<"cmp${p} $Rd, $imm",
-                   (CMNzri rGPR:$Rd, so_imm_neg:$imm, pred:$p)>;
+                   (CMNri rGPR:$Rd, so_imm_neg:$imm, pred:$p)>;
 def : ARMInstAlias<"cmn${p} $Rd, $imm",
                    (CMPri rGPR:$Rd, so_imm_neg:$imm, pred:$p)>;
 
diff --git a/lib/Target/ARM/ARMInstrThumb2.td b/lib/Target/ARM/ARMInstrThumb2.td
index c309f84b58..e3a1c8c8f4 100644
--- a/lib/Target/ARM/ARMInstrThumb2.td
+++ b/lib/Target/ARM/ARMInstrThumb2.td
@@ -2849,20 +2849,64 @@ def : T2Pat<(ARMcmpZ  GPRnopc:$lhs, rGPR:$rhs),
 def : T2Pat<(ARMcmpZ  GPRnopc:$lhs, t2_so_reg:$rhs),
             (t2CMPrs  GPRnopc:$lhs, t2_so_reg:$rhs)>;
 
-//FIXME: Disable CMN, as CCodes are backwards from compare expectations
-//       Compare-to-zero still works out, just not the relationals
-//defm t2CMN  : T2I_cmp_irs<0b1000, "cmn",
-//                          BinOpFrag<(ARMcmp node:$LHS,(ineg node:$RHS))>>;
-defm t2CMNz : T2I_cmp_irs<0b1000, "cmn",
-                          IIC_iCMPi, IIC_iCMPr, IIC_iCMPsi,
-                          BinOpFrag<(ARMcmpZ node:$LHS,(ineg node:$RHS))>,
-                          "t2CMNz">;
+let isCompare = 1, Defs = [CPSR] in {
+   // shifted imm
+   def t2CMNri : T2OneRegCmpImm<
+                (outs), (ins GPRnopc:$Rn, t2_so_imm:$imm), IIC_iCMPi,
+                "cmn", ".w\t$Rn, $imm",
+                [(ARMcmn GPRnopc:$Rn, (ineg t2_so_imm:$imm))]> {
+     let Inst{31-27} = 0b11110;
+     let Inst{25} = 0;
+     let Inst{24-21} = 0b1000;
+     let Inst{20} = 1; // The S bit.
+     let Inst{15} = 0;
+     let Inst{11-8} = 0b1111; // Rd
+   }
+   // register
+   def t2CMNzrr : T2TwoRegCmp<
+                (outs), (ins GPRnopc:$Rn, rGPR:$Rm), IIC_iCMPr,
+                "cmn", ".w\t$Rn, $Rm",
+                [(BinOpFrag<(ARMcmpZ node:$LHS,(ineg node:$RHS))>
+                  GPRnopc:$Rn, rGPR:$Rm)]> {
+     let Inst{31-27} = 0b11101;
+     let Inst{26-25} = 0b01;
+     let Inst{24-21} = 0b1000;
+     let Inst{20} = 1; // The S bit.
+     let Inst{14-12} = 0b000; // imm3
+     let Inst{11-8} = 0b1111; // Rd
+     let Inst{7-6} = 0b00; // imm2
+     let Inst{5-4} = 0b00; // type
+   }
+   // shifted register
+   def t2CMNzrs : T2OneRegCmpShiftedReg<
+                (outs), (ins GPRnopc:$Rn, t2_so_reg:$ShiftedRm), IIC_iCMPsi,
+                "cmn", ".w\t$Rn, $ShiftedRm",
+                [(BinOpFrag<(ARMcmpZ node:$LHS,(ineg node:$RHS))>
+                  GPRnopc:$Rn, t2_so_reg:$ShiftedRm)]> {
+     let Inst{31-27} = 0b11101;
+     let Inst{26-25} = 0b01;
+     let Inst{24-21} = 0b1000;
+     let Inst{20} = 1; // The S bit.
+     let Inst{11-8} = 0b1111; // Rd
+   }
+}
+
+// Assembler aliases w/o the ".w" suffix.
+// No alias here for 'rr' version as not all instantiations of this multiclass
+// want one (CMP in particular, does not).
+def : t2InstAlias<!strconcat("cmn", "${p}", " $Rn, $imm"),
+   (!cast<Instruction>(!strconcat("t2CMN", "ri")) GPRnopc:$Rn,
+                                                  t2_so_imm:$imm, pred:$p)>;
+def : t2InstAlias<!strconcat("cmn", "${p}", " $Rn, $shift"),
+   (!cast<Instruction>(!strconcat("t2CMNz", "rs")) GPRnopc:$Rn,
+                                                  t2_so_reg:$shift,
+                                                  pred:$p)>;
 
-//def : T2Pat<(ARMcmp  GPR:$src, t2_so_imm_neg:$imm),
-//            (t2CMNri GPR:$src, t2_so_imm_neg:$imm)>;
+def : T2Pat<(ARMcmp  GPR:$src, t2_so_imm_neg:$imm),
+            (t2CMNri GPR:$src, t2_so_imm_neg:$imm)>;
 
-def : T2Pat<(ARMcmpZ  GPRnopc:$src, t2_so_imm_neg:$imm),
-            (t2CMNzri GPRnopc:$src, t2_so_imm_neg:$imm)>;
+def : T2Pat<(ARMcmpZ GPRnopc:$src, t2_so_imm_neg:$imm),
+            (t2CMNri GPRnopc:$src, t2_so_imm_neg:$imm)>;
 
 defm t2TST  : T2I_cmp_irs<0b0000, "tst",
                           IIC_iTSTi, IIC_iTSTr, IIC_iTSTsi,
@@ -4224,7 +4268,7 @@ def : t2InstAlias<"add${s}${p} $Rd, $imm",
                            pred:$p, cc_out:$s)>;
 // Same for CMP <--> CMN via t2_so_imm_neg
 def : t2InstAlias<"cmp${p} $Rd, $imm",
-                  (t2CMNzri rGPR:$Rd, t2_so_imm_neg:$imm, pred:$p)>;
+                  (t2CMNri rGPR:$Rd, t2_so_imm_neg:$imm, pred:$p)>;
 def : t2InstAlias<"cmn${p} $Rd, $imm",
                   (t2CMPri rGPR:$Rd, t2_so_imm_neg:$imm, pred:$p)>;