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[SelectionDAG][X86] Fold sub(x, mul(divrem(x,y)[0], y)) to divrem(x, y)[1] #136565

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merged 3 commits into from
Apr 22, 2025
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[SelectionDAG][X86] Fold sub(x, mul(divrem(x,y)[0], y)) to divrem(x, y)[1] #136565

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el-ev Apr 22, 2025
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[SelectionDAG][X86] Fold `sub(x, mul(divrem(x,y)[0], y))` to `divrem(…
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58 changes: 58 additions & 0 deletions llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3867,6 +3867,61 @@ static SDValue foldSubCtlzNot(SDNode *N, SelectionDAG &DAG) {
return Matcher.getNode(ISD::CTLZ_ZERO_UNDEF, DL, VT, Not);
}

// Fold sub(x, mul(divrem(x,y)[0], y)) to divrem(x, y)[1]
static SDValue foldRemainderIdiom(SDNode *N, SelectionDAG &DAG, SDLoc &DL) {
assert(N->getOpcode() == ISD::SUB && "Node must be a SUB");
SDValue Sub0 = N->getOperand(0);
SDValue Sub1 = N->getOperand(1);

auto CheckAndFoldMulCase = [&](SDValue DivRem, SDValue MaybeY) -> SDValue {
if ((DivRem.getOpcode() == ISD::SDIVREM ||
DivRem.getOpcode() == ISD::UDIVREM) &&
DivRem.getResNo() == 0 && DivRem.getOperand(0) == Sub0 &&
DivRem.getOperand(1) == MaybeY) {
return SDValue(DivRem.getNode(), 1);
}
return SDValue();
};

if (Sub1.getOpcode() == ISD::MUL) {
// (sub x, (mul divrem(x,y)[0], y))
SDValue Mul0 = Sub1.getOperand(0);
SDValue Mul1 = Sub1.getOperand(1);

SDValue Res = CheckAndFoldMulCase(Mul0, Mul1);
if (Res)
return Res;

Res = CheckAndFoldMulCase(Mul1, Mul0);
if (Res)
return Res;

} else if (Sub1.getOpcode() == ISD::SHL) {
// Handle (sub x, (shl divrem(x,y)[0], C)) where y = 1 << C
SDValue Shl0 = Sub1.getOperand(0);
SDValue Shl1 = Sub1.getOperand(1);
// Check if Shl0 is divrem(x, Y)[0]
if ((Shl0.getOpcode() == ISD::SDIVREM ||
Shl0.getOpcode() == ISD::UDIVREM) &&
Shl0.getResNo() == 0 && Shl0.getOperand(0) == Sub0) {

SDValue Divisor = Shl0.getOperand(1);

ConstantSDNode *DivC = isConstOrConstSplat(Divisor);
ConstantSDNode *ShC = isConstOrConstSplat(Shl1);
if (!DivC || !ShC) {
return SDValue();
}

if (DivC->getAPIntValue().isPowerOf2() &&
DivC->getAPIntValue().logBase2() == ShC->getAPIntValue()) {
return SDValue(Shl0.getNode(), 1);
}
}
}
return SDValue();
}

// Since it may not be valid to emit a fold to zero for vector initializers
// check if we can before folding.
static SDValue tryFoldToZero(const SDLoc &DL, const TargetLowering &TLI, EVT VT,
Expand Down Expand Up @@ -4094,6 +4149,9 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
if (SDValue V = foldSubToUSubSat(VT, N, DL))
return V;

if (SDValue V = foldRemainderIdiom(N, DAG, DL))
return V;

// (A - B) - 1 -> add (xor B, -1), A
if (sd_match(N, m_Sub(m_OneUse(m_Sub(m_Value(A), m_Value(B))), m_One())))
return DAG.getNode(ISD::ADD, DL, VT, A, DAG.getNOT(DL, B, VT));
Expand Down
143 changes: 62 additions & 81 deletions llvm/test/CodeGen/X86/div-rem-pair-recomposition-signed.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -11,25 +11,20 @@
define i8 @scalar_i8(i8 %x, i8 %y, ptr %divdst) nounwind {
; X86-LABEL: scalar_i8:
; X86: # %bb.0:
; X86-NEXT: movsbl {{[0-9]+}}(%esp), %eax
; X86-NEXT: idivb {{[0-9]+}}(%esp)
; X86-NEXT: movl {{[0-9]+}}(%esp), %edx
; X86-NEXT: movb {{[0-9]+}}(%esp), %ch
; X86-NEXT: movb {{[0-9]+}}(%esp), %cl
; X86-NEXT: movsbl %cl, %eax
; X86-NEXT: idivb %ch
; X86-NEXT: movsbl %ah, %ecx
; X86-NEXT: movb %al, (%edx)
; X86-NEXT: mulb %ch
; X86-NEXT: subb %al, %cl
; X86-NEXT: movl %ecx, %eax
; X86-NEXT: retl
;
; X64-LABEL: scalar_i8:
; X64: # %bb.0:
; X64-NEXT: movsbl %dil, %ecx
; X64-NEXT: movl %ecx, %eax
; X64-NEXT: movsbl %dil, %eax
; X64-NEXT: idivb %sil
; X64-NEXT: movsbl %ah, %ecx
; X64-NEXT: movb %al, (%rdx)
; X64-NEXT: mulb %sil
; X64-NEXT: subb %al, %cl
; X64-NEXT: movl %ecx, %eax
; X64-NEXT: retq
%div = sdiv i8 %x, %y
Expand All @@ -42,34 +37,23 @@ define i8 @scalar_i8(i8 %x, i8 %y, ptr %divdst) nounwind {
define i16 @scalar_i16(i16 %x, i16 %y, ptr %divdst) nounwind {
; X86-LABEL: scalar_i16:
; X86: # %bb.0:
; X86-NEXT: pushl %edi
; X86-NEXT: pushl %esi
; X86-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X86-NEXT: movl {{[0-9]+}}(%esp), %esi
; X86-NEXT: movl {{[0-9]+}}(%esp), %edi
; X86-NEXT: movl %ecx, %eax
; X86-NEXT: movzwl {{[0-9]+}}(%esp), %eax
; X86-NEXT: cwtd
; X86-NEXT: idivw %si
; X86-NEXT: # kill: def $ax killed $ax def $eax
; X86-NEXT: movw %ax, (%edi)
; X86-NEXT: imull %eax, %esi
; X86-NEXT: subl %esi, %ecx
; X86-NEXT: movl %ecx, %eax
; X86-NEXT: popl %esi
; X86-NEXT: popl %edi
; X86-NEXT: idivw {{[0-9]+}}(%esp)
; X86-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X86-NEXT: movw %ax, (%ecx)
; X86-NEXT: movl %edx, %eax
; X86-NEXT: retl
;
; X64-LABEL: scalar_i16:
; X64: # %bb.0:
; X64-NEXT: movq %rdx, %rcx
; X64-NEXT: movl %edi, %eax
; X64-NEXT: # kill: def $ax killed $ax killed $eax
; X64-NEXT: cwtd
; X64-NEXT: idivw %si
; X64-NEXT: # kill: def $ax killed $ax def $eax
; X64-NEXT: movw %ax, (%rcx)
; X64-NEXT: imull %eax, %esi
; X64-NEXT: subl %esi, %edi
; X64-NEXT: movl %edi, %eax
; X64-NEXT: movl %edx, %eax
; X64-NEXT: retq
%div = sdiv i16 %x, %y
store i16 %div, ptr %divdst, align 4
Expand All @@ -81,20 +65,12 @@ define i16 @scalar_i16(i16 %x, i16 %y, ptr %divdst) nounwind {
define i32 @scalar_i32(i32 %x, i32 %y, ptr %divdst) nounwind {
; X86-LABEL: scalar_i32:
; X86: # %bb.0:
; X86-NEXT: pushl %edi
; X86-NEXT: pushl %esi
; X86-NEXT: movl {{[0-9]+}}(%esp), %esi
; X86-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X86-NEXT: movl {{[0-9]+}}(%esp), %edi
; X86-NEXT: movl %ecx, %eax
; X86-NEXT: movl {{[0-9]+}}(%esp), %eax
; X86-NEXT: cltd
; X86-NEXT: idivl %edi
; X86-NEXT: movl %eax, (%esi)
; X86-NEXT: imull %edi, %eax
; X86-NEXT: subl %eax, %ecx
; X86-NEXT: movl %ecx, %eax
; X86-NEXT: popl %esi
; X86-NEXT: popl %edi
; X86-NEXT: idivl {{[0-9]+}}(%esp)
; X86-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X86-NEXT: movl %eax, (%ecx)
; X86-NEXT: movl %edx, %eax
; X86-NEXT: retl
;
; X64-LABEL: scalar_i32:
Expand All @@ -104,9 +80,7 @@ define i32 @scalar_i32(i32 %x, i32 %y, ptr %divdst) nounwind {
; X64-NEXT: cltd
; X64-NEXT: idivl %esi
; X64-NEXT: movl %eax, (%rcx)
; X64-NEXT: imull %esi, %eax
; X64-NEXT: subl %eax, %edi
; X64-NEXT: movl %edi, %eax
; X64-NEXT: movl %edx, %eax
; X64-NEXT: retq
%div = sdiv i32 %x, %y
store i32 %div, ptr %divdst, align 4
Expand Down Expand Up @@ -158,9 +132,7 @@ define i64 @scalar_i64(i64 %x, i64 %y, ptr %divdst) nounwind {
; X64-NEXT: cqto
; X64-NEXT: idivq %rsi
; X64-NEXT: movq %rax, (%rcx)
; X64-NEXT: imulq %rsi, %rax
; X64-NEXT: subq %rax, %rdi
; X64-NEXT: movq %rdi, %rax
; X64-NEXT: movq %rdx, %rax
; X64-NEXT: retq
%div = sdiv i64 %x, %y
store i64 %div, ptr %divdst, align 4
Expand Down Expand Up @@ -1194,39 +1166,53 @@ define <2 x i64> @vector_i128_i64(<2 x i64> %x, <2 x i64> %y, ptr %divdst) nounw
ret <2 x i64> %t2
}

define i32 @scalar_i32_const_pow2_divisor(i32 %0, ptr %1) minsize nounwind {
; X86-LABEL: scalar_i32_const_pow2_divisor:
; X86: # %bb.0:
; X86-NEXT: movl {{[0-9]+}}(%esp), %eax
; X86-NEXT: movl $256, %ecx # imm = 0x100
; X86-NEXT: cltd
; X86-NEXT: idivl %ecx
; X86-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X86-NEXT: movl %edx, (%ecx)
; X86-NEXT: retl
;
; X64-LABEL: scalar_i32_const_pow2_divisor:
; X64: # %bb.0:
; X64-NEXT: movl %edi, %eax
; X64-NEXT: movl $256, %ecx # imm = 0x100
; X64-NEXT: cltd
; X64-NEXT: idivl %ecx
; X64-NEXT: movl %edx, (%rsi)
; X64-NEXT: retq
%3 = srem i32 %0, 256
store i32 %3, ptr %1, align 4
%4 = sdiv i32 %0, 256
ret i32 %4
}

; Special tests.

define i32 @scalar_i32_commutative(i32 %x, ptr %ysrc, ptr %divdst) nounwind {
; X86-LABEL: scalar_i32_commutative:
; X86: # %bb.0:
; X86-NEXT: pushl %edi
; X86-NEXT: pushl %esi
; X86-NEXT: movl {{[0-9]+}}(%esp), %esi
; X86-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X86-NEXT: movl {{[0-9]+}}(%esp), %eax
; X86-NEXT: movl (%eax), %edi
; X86-NEXT: movl %ecx, %eax
; X86-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X86-NEXT: cltd
; X86-NEXT: idivl %edi
; X86-NEXT: movl %eax, (%esi)
; X86-NEXT: imull %eax, %edi
; X86-NEXT: subl %edi, %ecx
; X86-NEXT: movl %ecx, %eax
; X86-NEXT: popl %esi
; X86-NEXT: popl %edi
; X86-NEXT: idivl (%ecx)
; X86-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X86-NEXT: movl %eax, (%ecx)
; X86-NEXT: movl %edx, %eax
; X86-NEXT: retl
;
; X64-LABEL: scalar_i32_commutative:
; X64: # %bb.0:
; X64-NEXT: movq %rdx, %rcx
; X64-NEXT: movl (%rsi), %esi
; X64-NEXT: movl %edi, %eax
; X64-NEXT: cltd
; X64-NEXT: idivl %esi
; X64-NEXT: idivl (%rsi)
; X64-NEXT: movl %eax, (%rcx)
; X64-NEXT: imull %eax, %esi
; X64-NEXT: subl %esi, %edi
; X64-NEXT: movl %edi, %eax
; X64-NEXT: movl %edx, %eax
; X64-NEXT: retq
%y = load i32, ptr %ysrc, align 4
%div = sdiv i32 %x, %y
Expand All @@ -1240,24 +1226,20 @@ define i32 @scalar_i32_commutative(i32 %x, ptr %ysrc, ptr %divdst) nounwind {
define i32 @extrause(i32 %x, i32 %y, ptr %divdst, ptr %t1dst) nounwind {
; X86-LABEL: extrause:
; X86: # %bb.0:
; X86-NEXT: pushl %ebx
; X86-NEXT: pushl %edi
; X86-NEXT: pushl %esi
; X86-NEXT: movl {{[0-9]+}}(%esp), %esi
; X86-NEXT: movl {{[0-9]+}}(%esp), %edi
; X86-NEXT: movl {{[0-9]+}}(%esp), %eax
; X86-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X86-NEXT: movl {{[0-9]+}}(%esp), %ebx
; X86-NEXT: movl %ecx, %eax
; X86-NEXT: cltd
; X86-NEXT: idivl %ebx
; X86-NEXT: idivl %ecx
; X86-NEXT: movl {{[0-9]+}}(%esp), %esi
; X86-NEXT: movl {{[0-9]+}}(%esp), %edi
; X86-NEXT: movl %eax, (%edi)
; X86-NEXT: imull %ebx, %eax
; X86-NEXT: imull %ecx, %eax
; X86-NEXT: movl %eax, (%esi)
; X86-NEXT: subl %eax, %ecx
; X86-NEXT: movl %ecx, %eax
; X86-NEXT: movl %edx, %eax
; X86-NEXT: popl %esi
; X86-NEXT: popl %edi
; X86-NEXT: popl %ebx
; X86-NEXT: retl
;
; X64-LABEL: extrause:
Expand All @@ -1269,8 +1251,7 @@ define i32 @extrause(i32 %x, i32 %y, ptr %divdst, ptr %t1dst) nounwind {
; X64-NEXT: movl %eax, (%r8)
; X64-NEXT: imull %esi, %eax
; X64-NEXT: movl %eax, (%rcx)
; X64-NEXT: subl %eax, %edi
; X64-NEXT: movl %edi, %eax
; X64-NEXT: movl %edx, %eax
; X64-NEXT: retq
%div = sdiv i32 %x, %y
store i32 %div, ptr %divdst, align 4
Expand All @@ -1296,14 +1277,14 @@ define i32 @multiple_bb(i32 %x, i32 %y, ptr %divdst, i1 zeroext %store_srem, ptr
; X86-NEXT: idivl %esi
; X86-NEXT: movl %eax, (%edi)
; X86-NEXT: testb %bl, %bl
; X86-NEXT: je .LBB11_2
; X86-NEXT: je .LBB12_2
; X86-NEXT: # %bb.1: # %do_srem
; X86-NEXT: movl {{[0-9]+}}(%esp), %edx
; X86-NEXT: movl %eax, %edi
; X86-NEXT: imull %esi, %edi
; X86-NEXT: subl %edi, %ecx
; X86-NEXT: movl %ecx, (%edx)
; X86-NEXT: .LBB11_2: # %end
; X86-NEXT: .LBB12_2: # %end
; X86-NEXT: popl %esi
; X86-NEXT: popl %edi
; X86-NEXT: popl %ebx
Expand All @@ -1317,13 +1298,13 @@ define i32 @multiple_bb(i32 %x, i32 %y, ptr %divdst, i1 zeroext %store_srem, ptr
; X64-NEXT: idivl %esi
; X64-NEXT: movl %eax, (%r9)
; X64-NEXT: testl %ecx, %ecx
; X64-NEXT: je .LBB11_2
; X64-NEXT: je .LBB12_2
; X64-NEXT: # %bb.1: # %do_srem
; X64-NEXT: movl %eax, %ecx
; X64-NEXT: imull %esi, %ecx
; X64-NEXT: subl %ecx, %edi
; X64-NEXT: movl %edi, (%r8)
; X64-NEXT: .LBB11_2: # %end
; X64-NEXT: .LBB12_2: # %end
; X64-NEXT: retq
%div = sdiv i32 %x, %y
store i32 %div, ptr %divdst, align 4
Expand Down
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