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Re-enable the CMN instruction.

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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>

llvm-svn: 158302
This commit is contained in:
Bill Wendling 2012-06-11 08:07:26 +00:00
parent f350a319b9
commit 2320ff76d7
6 changed files with 166 additions and 69 deletions
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4
lib/Target/ARM/ARMFastISel.cpp
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@ -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;
}

1
lib/Target/ARM/ARMISelLowering.cpp
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@ -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";

1
lib/Target/ARM/ARMISelLowering.h
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@ -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.

137
lib/Target/ARM/ARMInstrInfo.td
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@ -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)>;

70
lib/Target/ARM/ARMInstrThumb2.td
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@ -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:$ShiftedRm)]> {
let Inst{31-27} = 0b11101;
let Inst{26-25} = 0b01;
let Inst{24-21} = 0b1000;
let Inst{20} = 1; // The S bit.
let Inst{11-8} = 0b1111; // Rd
}
}
//def : T2Pat<(ARMcmp GPR:$src, t2_so_imm_neg:$imm),
// (t2CMNri GPR:$src, t2_so_imm_neg:$imm)>;
// Assembler aliases w/o the ".w" suffix.
// No alias here for 'rr' version as not all instantiations of this multiclass
// want one (CMP in particular, does not).
def : t2InstAlias<!strconcat("cmn", "${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<(ARMcmpZ GPRnopc:$src, t2_so_imm_neg:$imm),
(t2CMNzri GPRnopc:$src, t2_so_imm_neg:$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),
(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)>;

22
test/CodeGen/ARM/cmn.ll Normal file
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@ -0,0 +1,22 @@
; RUN: llc < %s -mtriple thumbv7-apple-ios | FileCheck %s
; <rdar://problem/7569620>
define i32 @compare_i_gt(i32 %a) {
entry:
; CHECK: compare_i_gt
; CHECK-NOT: mvn
; CHECK: cmn
%cmp = icmp sgt i32 %a, -78
%. = zext i1 %cmp to i32
ret i32 %.
}
define i32 @compare_r_eq(i32 %a, i32 %b) {
entry:
; CHECK: compare_r_eq
; CHECK: cmn
%sub = sub nsw i32 0, %b
%cmp = icmp eq i32 %a, %sub
%. = zext i1 %cmp to i32
ret i32 %.
}