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[Mips] In LowerShift*Parts, xor with bits-1 instead of -1. (#71149)
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If we start with an i128 shift, the initial shift amount would usually
have zeros in bit 8 and above. xoring the shift amount with -1 will set
those upper bits to 1. If DAGCombiner is able to prove those bits are
now 1, then the shift that uses the xor will be replaced with undef.
Which we don't want.

Reduce the xor constant to VT.bits-1 where VT is half the size of the
larger shift type. This avoids toggling the upper bits. The hardware
shift instruction only uses the lower bits of the shift amount. I assume
the code used NOT because the hardware doesn't use the upper bits, but
that isn't compatible with the LLVM poison semantics.

Fixes #71142.
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@topperc
topperc authored Nov 3, 2023
1 parent 7ccdad1 commit 8d24d39
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Showing 4 changed files with 46 additions and 44 deletions.
14 changes: 8 additions & 6 deletions llvm/lib/Target/Mips/MipsISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2593,12 +2593,13 @@ SDValue MipsTargetLowering::lowerShiftLeftParts(SDValue Op,
SDValue Shamt = Op.getOperand(2);
// if shamt < (VT.bits):
// lo = (shl lo, shamt)
// hi = (or (shl hi, shamt) (srl (srl lo, 1), ~shamt))
// hi = (or (shl hi, shamt) (srl (srl lo, 1), (xor shamt, (VT.bits-1))))
// else:
// lo = 0
// hi = (shl lo, shamt[4:0])
SDValue Not = DAG.getNode(ISD::XOR, DL, MVT::i32, Shamt,
DAG.getConstant(-1, DL, MVT::i32));
SDValue Not =
DAG.getNode(ISD::XOR, DL, MVT::i32, Shamt,
DAG.getConstant(VT.getSizeInBits() - 1, DL, MVT::i32));
SDValue ShiftRight1Lo = DAG.getNode(ISD::SRL, DL, VT, Lo,
DAG.getConstant(1, DL, VT));
SDValue ShiftRightLo = DAG.getNode(ISD::SRL, DL, VT, ShiftRight1Lo, Not);
Expand All @@ -2623,7 +2624,7 @@ SDValue MipsTargetLowering::lowerShiftRightParts(SDValue Op, SelectionDAG &DAG,
MVT VT = Subtarget.isGP64bit() ? MVT::i64 : MVT::i32;

// if shamt < (VT.bits):
// lo = (or (shl (shl hi, 1), ~shamt) (srl lo, shamt))
// lo = (or (shl (shl hi, 1), (xor shamt, (VT.bits-1))) (srl lo, shamt))
// if isSRA:
// hi = (sra hi, shamt)
// else:
Expand All @@ -2635,8 +2636,9 @@ SDValue MipsTargetLowering::lowerShiftRightParts(SDValue Op, SelectionDAG &DAG,
// else:
// lo = (srl hi, shamt[4:0])
// hi = 0
SDValue Not = DAG.getNode(ISD::XOR, DL, MVT::i32, Shamt,
DAG.getConstant(-1, DL, MVT::i32));
SDValue Not =
DAG.getNode(ISD::XOR, DL, MVT::i32, Shamt,
DAG.getConstant(VT.getSizeInBits() - 1, DL, MVT::i32));
SDValue ShiftLeft1Hi = DAG.getNode(ISD::SHL, DL, VT, Hi,
DAG.getConstant(1, DL, VT));
SDValue ShiftLeftHi = DAG.getNode(ISD::SHL, DL, VT, ShiftLeft1Hi, Not);
Expand Down
24 changes: 12 additions & 12 deletions llvm/test/CodeGen/Mips/llvm-ir/ashr.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -280,7 +280,7 @@ define signext i64 @ashr_i64(i64 signext %a, i64 signext %b) {
; MIPS-NEXT: srav $3, $4, $7
; MIPS-NEXT: # %bb.1: # %entry
; MIPS-NEXT: srlv $1, $5, $7
; MIPS-NEXT: not $2, $7
; MIPS-NEXT: xori $2, $7, 31
; MIPS-NEXT: sll $4, $4, 1
; MIPS-NEXT: sllv $2, $4, $2
; MIPS-NEXT: or $1, $2, $1
Expand All @@ -294,7 +294,7 @@ define signext i64 @ashr_i64(i64 signext %a, i64 signext %b) {
; MIPS32-LABEL: ashr_i64:
; MIPS32: # %bb.0: # %entry
; MIPS32-NEXT: srlv $1, $5, $7
; MIPS32-NEXT: not $2, $7
; MIPS32-NEXT: xori $2, $7, 31
; MIPS32-NEXT: sll $3, $4, 1
; MIPS32-NEXT: sllv $2, $3, $2
; MIPS32-NEXT: or $3, $2, $1
Expand All @@ -308,7 +308,7 @@ define signext i64 @ashr_i64(i64 signext %a, i64 signext %b) {
; 32R2-LABEL: ashr_i64:
; 32R2: # %bb.0: # %entry
; 32R2-NEXT: srlv $1, $5, $7
; 32R2-NEXT: not $2, $7
; 32R2-NEXT: xori $2, $7, 31
; 32R2-NEXT: sll $3, $4, 1
; 32R2-NEXT: sllv $2, $3, $2
; 32R2-NEXT: or $3, $2, $1
Expand All @@ -328,7 +328,7 @@ define signext i64 @ashr_i64(i64 signext %a, i64 signext %b) {
; 32R6-NEXT: selnez $6, $6, $3
; 32R6-NEXT: or $2, $6, $2
; 32R6-NEXT: srlv $5, $5, $7
; 32R6-NEXT: not $6, $7
; 32R6-NEXT: xori $6, $7, 31
; 32R6-NEXT: sll $4, $4, 1
; 32R6-NEXT: sllv $4, $4, $6
; 32R6-NEXT: or $4, $4, $5
Expand Down Expand Up @@ -360,9 +360,9 @@ define signext i64 @ashr_i64(i64 signext %a, i64 signext %b) {
; MMR3-LABEL: ashr_i64:
; MMR3: # %bb.0: # %entry
; MMR3-NEXT: srlv $2, $5, $7
; MMR3-NEXT: not16 $3, $7
; MMR3-NEXT: sll16 $5, $4, 1
; MMR3-NEXT: sllv $3, $5, $3
; MMR3-NEXT: xori $1, $7, 31
; MMR3-NEXT: sll16 $3, $4, 1
; MMR3-NEXT: sllv $3, $3, $1
; MMR3-NEXT: or16 $3, $2
; MMR3-NEXT: srav $2, $4, $7
; MMR3-NEXT: andi16 $5, $7, 32
Expand All @@ -380,7 +380,7 @@ define signext i64 @ashr_i64(i64 signext %a, i64 signext %b) {
; MMR6-NEXT: selnez $6, $6, $3
; MMR6-NEXT: or $2, $6, $2
; MMR6-NEXT: srlv $5, $5, $7
; MMR6-NEXT: not16 $6, $7
; MMR6-NEXT: xori $6, $7, 31
; MMR6-NEXT: sll16 $4, $4, 1
; MMR6-NEXT: sllv $4, $4, $6
; MMR6-NEXT: or $4, $4, $5
Expand Down Expand Up @@ -609,7 +609,7 @@ define signext i128 @ashr_i128(i128 signext %a, i128 signext %b) {
; MIPS3-NEXT: # %bb.1: # %entry
; MIPS3-NEXT: dsrlv $1, $5, $7
; MIPS3-NEXT: dsll $4, $4, 1
; MIPS3-NEXT: not $2, $2
; MIPS3-NEXT: xori $2, $2, 63
; MIPS3-NEXT: dsllv $2, $4, $2
; MIPS3-NEXT: or $1, $2, $1
; MIPS3-NEXT: move $2, $3
Expand All @@ -624,7 +624,7 @@ define signext i128 @ashr_i128(i128 signext %a, i128 signext %b) {
; MIPS64-NEXT: dsrlv $1, $5, $7
; MIPS64-NEXT: dsll $2, $4, 1
; MIPS64-NEXT: sll $5, $7, 0
; MIPS64-NEXT: not $3, $5
; MIPS64-NEXT: xori $3, $5, 63
; MIPS64-NEXT: dsllv $2, $2, $3
; MIPS64-NEXT: or $3, $2, $1
; MIPS64-NEXT: dsrav $2, $4, $7
Expand All @@ -639,7 +639,7 @@ define signext i128 @ashr_i128(i128 signext %a, i128 signext %b) {
; MIPS64R2-NEXT: dsrlv $1, $5, $7
; MIPS64R2-NEXT: dsll $2, $4, 1
; MIPS64R2-NEXT: sll $5, $7, 0
; MIPS64R2-NEXT: not $3, $5
; MIPS64R2-NEXT: xori $3, $5, 63
; MIPS64R2-NEXT: dsllv $2, $2, $3
; MIPS64R2-NEXT: or $3, $2, $1
; MIPS64R2-NEXT: dsrav $2, $4, $7
Expand All @@ -661,7 +661,7 @@ define signext i128 @ashr_i128(i128 signext %a, i128 signext %b) {
; MIPS64R6-NEXT: or $2, $8, $2
; MIPS64R6-NEXT: dsrlv $5, $5, $7
; MIPS64R6-NEXT: dsll $4, $4, 1
; MIPS64R6-NEXT: not $3, $3
; MIPS64R6-NEXT: xori $3, $3, 63
; MIPS64R6-NEXT: dsllv $3, $4, $3
; MIPS64R6-NEXT: or $3, $3, $5
; MIPS64R6-NEXT: seleqz $3, $3, $6
Expand Down
26 changes: 13 additions & 13 deletions llvm/test/CodeGen/Mips/llvm-ir/lshr.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -283,7 +283,7 @@ define signext i64 @lshr_i64(i64 signext %a, i64 signext %b) {
; MIPS2-NEXT: addiu $2, $zero, 0
; MIPS2-NEXT: # %bb.1: # %entry
; MIPS2-NEXT: srlv $1, $5, $7
; MIPS2-NEXT: not $2, $7
; MIPS2-NEXT: xori $2, $7, 31
; MIPS2-NEXT: sll $3, $4, 1
; MIPS2-NEXT: sllv $2, $3, $2
; MIPS2-NEXT: or $3, $2, $1
Expand All @@ -296,7 +296,7 @@ define signext i64 @lshr_i64(i64 signext %a, i64 signext %b) {
; MIPS32-LABEL: lshr_i64:
; MIPS32: # %bb.0: # %entry
; MIPS32-NEXT: srlv $1, $5, $7
; MIPS32-NEXT: not $2, $7
; MIPS32-NEXT: xori $2, $7, 31
; MIPS32-NEXT: sll $3, $4, 1
; MIPS32-NEXT: sllv $2, $3, $2
; MIPS32-NEXT: or $3, $2, $1
Expand All @@ -309,7 +309,7 @@ define signext i64 @lshr_i64(i64 signext %a, i64 signext %b) {
; MIPS32R2-LABEL: lshr_i64:
; MIPS32R2: # %bb.0: # %entry
; MIPS32R2-NEXT: srlv $1, $5, $7
; MIPS32R2-NEXT: not $2, $7
; MIPS32R2-NEXT: xori $2, $7, 31
; MIPS32R2-NEXT: sll $3, $4, 1
; MIPS32R2-NEXT: sllv $2, $3, $2
; MIPS32R2-NEXT: or $3, $2, $1
Expand All @@ -322,7 +322,7 @@ define signext i64 @lshr_i64(i64 signext %a, i64 signext %b) {
; MIPS32R6-LABEL: lshr_i64:
; MIPS32R6: # %bb.0: # %entry
; MIPS32R6-NEXT: srlv $1, $5, $7
; MIPS32R6-NEXT: not $2, $7
; MIPS32R6-NEXT: xori $2, $7, 31
; MIPS32R6-NEXT: sll $3, $4, 1
; MIPS32R6-NEXT: sllv $2, $3, $2
; MIPS32R6-NEXT: or $1, $2, $1
Expand Down Expand Up @@ -362,9 +362,9 @@ define signext i64 @lshr_i64(i64 signext %a, i64 signext %b) {
; MMR3-LABEL: lshr_i64:
; MMR3: # %bb.0: # %entry
; MMR3-NEXT: srlv $2, $5, $7
; MMR3-NEXT: not16 $3, $7
; MMR3-NEXT: sll16 $5, $4, 1
; MMR3-NEXT: sllv $3, $5, $3
; MMR3-NEXT: xori $1, $7, 31
; MMR3-NEXT: sll16 $3, $4, 1
; MMR3-NEXT: sllv $3, $3, $1
; MMR3-NEXT: or16 $3, $2
; MMR3-NEXT: srlv $2, $4, $7
; MMR3-NEXT: andi16 $4, $7, 32
Expand All @@ -376,7 +376,7 @@ define signext i64 @lshr_i64(i64 signext %a, i64 signext %b) {
; MMR6-LABEL: lshr_i64:
; MMR6: # %bb.0: # %entry
; MMR6-NEXT: srlv $1, $5, $7
; MMR6-NEXT: not16 $2, $7
; MMR6-NEXT: xori $2, $7, 31
; MMR6-NEXT: sll16 $3, $4, 1
; MMR6-NEXT: sllv $2, $3, $2
; MMR6-NEXT: or $1, $2, $1
Expand Down Expand Up @@ -606,7 +606,7 @@ define signext i128 @lshr_i128(i128 signext %a, i128 signext %b) {
; MIPS3-NEXT: # %bb.1: # %entry
; MIPS3-NEXT: dsrlv $1, $5, $7
; MIPS3-NEXT: dsll $2, $4, 1
; MIPS3-NEXT: not $3, $3
; MIPS3-NEXT: xori $3, $3, 63
; MIPS3-NEXT: dsllv $2, $2, $3
; MIPS3-NEXT: or $3, $2, $1
; MIPS3-NEXT: jr $ra
Expand All @@ -620,7 +620,7 @@ define signext i128 @lshr_i128(i128 signext %a, i128 signext %b) {
; MIPS4-NEXT: dsrlv $1, $5, $7
; MIPS4-NEXT: dsll $2, $4, 1
; MIPS4-NEXT: sll $5, $7, 0
; MIPS4-NEXT: not $3, $5
; MIPS4-NEXT: xori $3, $5, 63
; MIPS4-NEXT: dsllv $2, $2, $3
; MIPS4-NEXT: or $3, $2, $1
; MIPS4-NEXT: dsrlv $2, $4, $7
Expand All @@ -634,7 +634,7 @@ define signext i128 @lshr_i128(i128 signext %a, i128 signext %b) {
; MIPS64-NEXT: dsrlv $1, $5, $7
; MIPS64-NEXT: dsll $2, $4, 1
; MIPS64-NEXT: sll $5, $7, 0
; MIPS64-NEXT: not $3, $5
; MIPS64-NEXT: xori $3, $5, 63
; MIPS64-NEXT: dsllv $2, $2, $3
; MIPS64-NEXT: or $3, $2, $1
; MIPS64-NEXT: dsrlv $2, $4, $7
Expand All @@ -648,7 +648,7 @@ define signext i128 @lshr_i128(i128 signext %a, i128 signext %b) {
; MIPS64R2-NEXT: dsrlv $1, $5, $7
; MIPS64R2-NEXT: dsll $2, $4, 1
; MIPS64R2-NEXT: sll $5, $7, 0
; MIPS64R2-NEXT: not $3, $5
; MIPS64R2-NEXT: xori $3, $5, 63
; MIPS64R2-NEXT: dsllv $2, $2, $3
; MIPS64R2-NEXT: or $3, $2, $1
; MIPS64R2-NEXT: dsrlv $2, $4, $7
Expand All @@ -662,7 +662,7 @@ define signext i128 @lshr_i128(i128 signext %a, i128 signext %b) {
; MIPS64R6-NEXT: dsrlv $1, $5, $7
; MIPS64R6-NEXT: dsll $2, $4, 1
; MIPS64R6-NEXT: sll $3, $7, 0
; MIPS64R6-NEXT: not $5, $3
; MIPS64R6-NEXT: xori $5, $3, 63
; MIPS64R6-NEXT: dsllv $2, $2, $5
; MIPS64R6-NEXT: or $1, $2, $1
; MIPS64R6-NEXT: andi $2, $3, 64
Expand Down
26 changes: 13 additions & 13 deletions llvm/test/CodeGen/Mips/llvm-ir/shl.ll
View file
Original file line number Diff line number Diff line change
Expand Up @@ -343,7 +343,7 @@ define signext i64 @shl_i64(i64 signext %a, i64 signext %b) {
; MIPS2-NEXT: nop
; MIPS2-NEXT: $BB4_3: # %entry
; MIPS2-NEXT: sllv $1, $4, $7
; MIPS2-NEXT: not $2, $7
; MIPS2-NEXT: xori $2, $7, 31
; MIPS2-NEXT: srl $3, $5, 1
; MIPS2-NEXT: srlv $2, $3, $2
; MIPS2-NEXT: or $2, $1, $2
Expand All @@ -356,7 +356,7 @@ define signext i64 @shl_i64(i64 signext %a, i64 signext %b) {
; MIPS32-LABEL: shl_i64:
; MIPS32: # %bb.0: # %entry
; MIPS32-NEXT: sllv $1, $4, $7
; MIPS32-NEXT: not $2, $7
; MIPS32-NEXT: xori $2, $7, 31
; MIPS32-NEXT: srl $3, $5, 1
; MIPS32-NEXT: srlv $2, $3, $2
; MIPS32-NEXT: or $2, $1, $2
Expand All @@ -369,7 +369,7 @@ define signext i64 @shl_i64(i64 signext %a, i64 signext %b) {
; MIPS32R2-LABEL: shl_i64:
; MIPS32R2: # %bb.0: # %entry
; MIPS32R2-NEXT: sllv $1, $4, $7
; MIPS32R2-NEXT: not $2, $7
; MIPS32R2-NEXT: xori $2, $7, 31
; MIPS32R2-NEXT: srl $3, $5, 1
; MIPS32R2-NEXT: srlv $2, $3, $2
; MIPS32R2-NEXT: or $2, $1, $2
Expand All @@ -382,7 +382,7 @@ define signext i64 @shl_i64(i64 signext %a, i64 signext %b) {
; MIPS32R6-LABEL: shl_i64:
; MIPS32R6: # %bb.0: # %entry
; MIPS32R6-NEXT: sllv $1, $4, $7
; MIPS32R6-NEXT: not $2, $7
; MIPS32R6-NEXT: xori $2, $7, 31
; MIPS32R6-NEXT: srl $3, $5, 1
; MIPS32R6-NEXT: srlv $2, $3, $2
; MIPS32R6-NEXT: or $1, $1, $2
Expand Down Expand Up @@ -422,9 +422,9 @@ define signext i64 @shl_i64(i64 signext %a, i64 signext %b) {
; MMR3-LABEL: shl_i64:
; MMR3: # %bb.0: # %entry
; MMR3-NEXT: sllv $3, $4, $7
; MMR3-NEXT: not16 $2, $7
; MMR3-NEXT: srl16 $4, $5, 1
; MMR3-NEXT: srlv $2, $4, $2
; MMR3-NEXT: xori $1, $7, 31
; MMR3-NEXT: srl16 $2, $5, 1
; MMR3-NEXT: srlv $2, $2, $1
; MMR3-NEXT: or16 $2, $3
; MMR3-NEXT: sllv $3, $5, $7
; MMR3-NEXT: andi16 $4, $7, 32
Expand All @@ -436,7 +436,7 @@ define signext i64 @shl_i64(i64 signext %a, i64 signext %b) {
; MMR6-LABEL: shl_i64:
; MMR6: # %bb.0: # %entry
; MMR6-NEXT: sllv $1, $4, $7
; MMR6-NEXT: not16 $2, $7
; MMR6-NEXT: xori $2, $7, 31
; MMR6-NEXT: srl16 $3, $5, 1
; MMR6-NEXT: srlv $2, $3, $2
; MMR6-NEXT: or $1, $1, $2
Expand Down Expand Up @@ -668,7 +668,7 @@ define signext i128 @shl_i128(i128 signext %a, i128 signext %b) {
; MIPS3-NEXT: .LBB5_3: # %entry
; MIPS3-NEXT: dsllv $1, $4, $7
; MIPS3-NEXT: dsrl $2, $5, 1
; MIPS3-NEXT: not $3, $3
; MIPS3-NEXT: xori $3, $3, 63
; MIPS3-NEXT: dsrlv $2, $2, $3
; MIPS3-NEXT: or $2, $1, $2
; MIPS3-NEXT: bnez $8, .LBB5_2
Expand All @@ -682,7 +682,7 @@ define signext i128 @shl_i128(i128 signext %a, i128 signext %b) {
; MIPS4-NEXT: dsllv $1, $4, $7
; MIPS4-NEXT: dsrl $2, $5, 1
; MIPS4-NEXT: sll $4, $7, 0
; MIPS4-NEXT: not $3, $4
; MIPS4-NEXT: xori $3, $4, 63
; MIPS4-NEXT: dsrlv $2, $2, $3
; MIPS4-NEXT: or $2, $1, $2
; MIPS4-NEXT: dsllv $3, $5, $7
Expand All @@ -696,7 +696,7 @@ define signext i128 @shl_i128(i128 signext %a, i128 signext %b) {
; MIPS64-NEXT: dsllv $1, $4, $7
; MIPS64-NEXT: dsrl $2, $5, 1
; MIPS64-NEXT: sll $4, $7, 0
; MIPS64-NEXT: not $3, $4
; MIPS64-NEXT: xori $3, $4, 63
; MIPS64-NEXT: dsrlv $2, $2, $3
; MIPS64-NEXT: or $2, $1, $2
; MIPS64-NEXT: dsllv $3, $5, $7
Expand All @@ -710,7 +710,7 @@ define signext i128 @shl_i128(i128 signext %a, i128 signext %b) {
; MIPS64R2-NEXT: dsllv $1, $4, $7
; MIPS64R2-NEXT: dsrl $2, $5, 1
; MIPS64R2-NEXT: sll $4, $7, 0
; MIPS64R2-NEXT: not $3, $4
; MIPS64R2-NEXT: xori $3, $4, 63
; MIPS64R2-NEXT: dsrlv $2, $2, $3
; MIPS64R2-NEXT: or $2, $1, $2
; MIPS64R2-NEXT: dsllv $3, $5, $7
Expand All @@ -724,7 +724,7 @@ define signext i128 @shl_i128(i128 signext %a, i128 signext %b) {
; MIPS64R6-NEXT: dsllv $1, $4, $7
; MIPS64R6-NEXT: dsrl $2, $5, 1
; MIPS64R6-NEXT: sll $3, $7, 0
; MIPS64R6-NEXT: not $4, $3
; MIPS64R6-NEXT: xori $4, $3, 63
; MIPS64R6-NEXT: dsrlv $2, $2, $4
; MIPS64R6-NEXT: or $1, $1, $2
; MIPS64R6-NEXT: andi $2, $3, 64
Expand Down

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