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[InstCombine] Convert or concat to fshl if opposite or concat exists #68502

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Nov 20, 2023
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[InstCombine] Convert or concat to fshl if opposite or concat exists #68502

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5b3b1bb
[InstCombine] Refactor matchFunnelShift to allow more pattern (NFC)
HaohaiWen Oct 7, 2023
68ab662
[InstCombine] Convert or concat to fshl if opposite or concat exists
HaohaiWen Oct 7, 2023
aca9aa3
Merge remote-tracking branch 'origin/main' into concat
HaohaiWen Oct 19, 2023
b7810a1
Support padding zero between high and low.
HaohaiWen Oct 20, 2023
116e529
Simplify code. Add more tests
HaohaiWen Oct 23, 2023
c882da8
Fix nuw flag
HaohaiWen Oct 24, 2023
fb1af49
Merge remote-tracking branch 'origin/main' into concat
HaohaiWen Nov 15, 2023
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45 changes: 43 additions & 2 deletions llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2735,7 +2735,8 @@ Instruction *InstCombinerImpl::matchBSwapOrBitReverse(Instruction &I,
}

/// Match UB-safe variants of the funnel shift intrinsic.
static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC) {
static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
const DominatorTree &DT) {
// TODO: Can we reduce the code duplication between this and the related
// rotate matching code under visitSelect and visitTrunc?
unsigned Width = Or.getType()->getScalarSizeInBits();
Expand Down Expand Up @@ -2840,6 +2841,46 @@ static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC) {
return nullptr;

FShiftArgs = {ShVal0, ShVal1, ShAmt};
} else if (isa<ZExtInst>(Or0) || isa<ZExtInst>(Or1)) {
// If there are two 'or' instructions concat variables in opposite order,
// the latter one can be safely convert to fshl.
//
// LowHigh = or (shl (zext Low), Width - ZextHighShlAmt), (zext High)
// HighLow = or (shl (zext High), ZextHighShlAmt), (zext Low)
// ->
// HighLow = fshl LowHigh, LowHigh, ZextHighShlAmt
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if (!isa<ZExtInst>(Or1))
std::swap(Or0, Or1);

Value *High, *ZextHigh, *Low;
const APInt *ZextHighShlAmt;
if (!match(Or0,
m_OneUse(m_Shl(m_Value(ZextHigh), m_APInt(ZextHighShlAmt)))))
return nullptr;

if (!match(Or1, m_ZExt(m_Value(Low))) ||
!match(ZextHigh, m_ZExt(m_Value(High))))
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Do you actually need the shifted value to be zext? I.e if you have (shl (zext i24 to i32), 8) that is bitwise equivilent to (shl i32, 8)

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If we only match (shl i32, 8), we can't guarantee it's reverse concat since we don't know if the most significant 8bit in i32 is zero.

%zext.x = zext i8 %x to i32 
%slx = shl nuw i32 %zext.x, 24 
%zext.y = zext i24 %y to i32 
%xy = or i32 %zext.y, %slx        #[x[7:0], y[23:0]]
%sly = shl nuw i32 %zext.y, 8 
%yx = or i32 %zext.x, %sly        #[y[23:0], x[7:0]]

If not match zext:

%zext.x = zext i8 %x to i32 
%slx = shl nuw i32 %zext.x, 24 
%xy = or i32 %y, %slx              #[unknown, y[23,0]]             y[31:24] may not be zero.
%sly = shl nuw i32 %y, 8           #[y[23:0], 0,0,0,0,0,0,0,0]
%yx = or i32 %zext.x, %sly         #[y[23:0], x[7:0]]

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Ahh, I see, although could handle masking and. Really its just a knownbits check though.

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I think we don't need to check zext. An example without zext: https://alive2.llvm.org/ce/z/MytePb

return nullptr;

unsigned HighSize = High->getType()->getScalarSizeInBits();
unsigned LowSize = Low->getType()->getScalarSizeInBits();
if (*ZextHighShlAmt != LowSize || HighSize + LowSize != Width)
return nullptr;

for (User *U : ZextHigh->users()) {
Value *X, *Y;
if (!match(U, m_Or(m_Value(X), m_Value(Y))))
continue;

if (!isa<ZExtInst>(Y))
std::swap(X, Y);

if (match(X, m_Shl(m_Specific(Or1), m_SpecificInt(HighSize))) &&
match(Y, m_Specific(ZextHigh)) && DT.dominates(U, &Or)) {
FShiftArgs = {U, U, ConstantInt::get(Or0->getType(), *ZextHighShlAmt)};
break;
}
}
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}

if (FShiftArgs.empty())
Expand Down Expand Up @@ -3341,7 +3382,7 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
/*MatchBitReversals*/ true))
return BitOp;

if (Instruction *Funnel = matchFunnelShift(I, *this))
if (Instruction *Funnel = matchFunnelShift(I, *this, DT))
return Funnel;

if (Instruction *Concat = matchOrConcat(I, Builder))
Expand Down
42 changes: 42 additions & 0 deletions llvm/test/Transforms/InstCombine/funnel.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -354,6 +354,48 @@ define <2 x i64> @fshl_select_vector(<2 x i64> %x, <2 x i64> %y, <2 x i64> %sham
ret <2 x i64> %r
}

; Convert 'or concat' to fshl if opposite 'or concat' exists.

define i32 @fshl_concat(i8 %x, i24 %y, ptr %addr) {
; CHECK-LABEL: @fshl_concat(
; CHECK-NEXT: [[ZEXT_X:%.*]] = zext i8 [[X:%.*]] to i32
; CHECK-NEXT: [[SLX:%.*]] = shl nuw i32 [[ZEXT_X]], 24
; CHECK-NEXT: [[ZEXT_Y:%.*]] = zext i24 [[Y:%.*]] to i32
; CHECK-NEXT: [[XY:%.*]] = or i32 [[SLX]], [[ZEXT_Y]]
; CHECK-NEXT: store i32 [[XY]], ptr [[ADDR:%.*]], align 4
; CHECK-NEXT: [[YX:%.*]] = call i32 @llvm.fshl.i32(i32 [[XY]], i32 [[XY]], i32 8)
; CHECK-NEXT: ret i32 [[YX]]
;
%zext.x = zext i8 %x to i32
%slx = shl nuw i32 %zext.x, 24
%zext.y = zext i24 %y to i32
%xy = or i32 %zext.y, %slx
store i32 %xy, ptr %addr, align 4
%sly = shl nuw i32 %zext.y, 8
%yx = or i32 %zext.x, %sly
ret i32 %yx
}

define <2 x i32> @fshl_concat_vector(<2 x i8> %x, <2 x i24> %y, ptr %addr) {
; CHECK-LABEL: @fshl_concat_vector(
; CHECK-NEXT: [[ZEXT_X:%.*]] = zext <2 x i8> [[X:%.*]] to <2 x i32>
; CHECK-NEXT: [[SLX:%.*]] = shl nuw <2 x i32> [[ZEXT_X]], <i32 24, i32 24>
; CHECK-NEXT: [[ZEXT_Y:%.*]] = zext <2 x i24> [[Y:%.*]] to <2 x i32>
; CHECK-NEXT: [[XY:%.*]] = or <2 x i32> [[SLX]], [[ZEXT_Y]]
; CHECK-NEXT: store <2 x i32> [[XY]], ptr [[ADDR:%.*]], align 4
; CHECK-NEXT: [[YX:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[XY]], <2 x i32> [[XY]], <2 x i32> <i32 8, i32 8>)
; CHECK-NEXT: ret <2 x i32> [[YX]]
;
%zext.x = zext <2 x i8> %x to <2 x i32>
%slx = shl nuw <2 x i32> %zext.x, <i32 24, i32 24>
%zext.y = zext <2 x i24> %y to <2 x i32>
%xy = or <2 x i32> %slx, %zext.y
store <2 x i32> %xy, ptr %addr, align 4
%sly = shl nuw <2 x i32> %zext.y, <i32 8, i32 8>
%yx = or <2 x i32> %sly, %zext.x
ret <2 x i32> %yx
}
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; Negative test - an oversized shift in the narrow type would produce the wrong value.

define i8 @unmasked_shlop_unmasked_shift_amount(i32 %x, i32 %y, i32 %shamt) {
Expand Down