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

1 files changed, 83 insertions, 54 deletions

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)>;