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Revert "[InstSimplify] Bypass no-op and-mask, using known bits (PR49543)"

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This reverts commit ea1a0d7c9ae3e5232a4163fc67efad4aabd51f2b.

While this is strictly more powerful, it is also strictly slower.
InstSimplify intentionally does not perform many folds that it
is allowed to perform, if doing so requires a KnownBits calculation
that will be repeated in InstCombine.

Maybe it's worthwhile to do this here, but that needs a more
explicitly stated motivation, evaluated in a review.
This commit is contained in:
Nikita Popov 2021-04-21 09:44:54 +02:00
parent 1ea67899d6
commit f8a60b9733
2 changed files with 16 additions and 6 deletions
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16
lib/Analysis/InstructionSimplify.cpp
View File

@ -2081,12 +2081,21 @@ static Value *SimplifyAndInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
if (Value *V = simplifyLogicOfAddSub(Op0, Op1, Instruction::And))
return V;
// A mask that only clears known zeros of a value is a no-op.
// A mask that only clears known zeros of a shifted value is a no-op.
Value *X;
const APInt *Mask;
const APInt *ShAmt;
if (match(Op1, m_APInt(Mask))) {
KnownBits Known = computeKnownBits(Op0, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
if ((~*Mask).isSubsetOf(Known.Zero))
// If all bits in the inverted and shifted mask are clear:
// and (shl X, ShAmt), Mask --> shl X, ShAmt
if (match(Op0, m_Shl(m_Value(X), m_APInt(ShAmt))) &&
(~(*Mask)).lshr(*ShAmt).isNullValue())
return Op0;
// If all bits in the inverted and shifted mask are clear:
// and (lshr X, ShAmt), Mask --> lshr X, ShAmt
if (match(Op0, m_LShr(m_Value(X), m_APInt(ShAmt))) &&
(~(*Mask)).shl(*ShAmt).isNullValue())
return Op0;
}
@ -2171,7 +2180,6 @@ static Value *SimplifyAndInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
// SimplifyDemandedBits in InstCombine can optimize the general case.
// This pattern aims to help other passes for a common case.
Value *Y, *XShifted;
const APInt *ShAmt;
if (match(Op1, m_APInt(Mask)) &&
match(Op0, m_c_Or(m_CombineAnd(m_NUWShl(m_Value(X), m_APInt(ShAmt)),
m_Value(XShifted)),

6
test/Transforms/InstSimplify/AndOrXor.ll
View File

@ -1192,7 +1192,8 @@ define i8 @noop_and_t0(i8 %x) {
; CHECK-LABEL: @noop_and_t0(
; CHECK-NEXT: [[A:%.*]] = shl i8 [[X:%.*]], 3
; CHECK-NEXT: [[B:%.*]] = lshr i8 [[A]], 2
; CHECK-NEXT: ret i8 [[B]]
; CHECK-NEXT: [[R:%.*]] = and i8 [[B]], 62
; CHECK-NEXT: ret i8 [[R]]
;
%a = shl i8 %x, 3
%b = lshr i8 %a, 2
@ -1203,7 +1204,8 @@ define i8 @noop_and_t1(i8 %x) {
; CHECK-LABEL: @noop_and_t1(
; CHECK-NEXT: [[A:%.*]] = shl i8 [[X:%.*]], 3
; CHECK-NEXT: [[B:%.*]] = lshr i8 [[A]], 2
; CHECK-NEXT: ret i8 [[B]]
; CHECK-NEXT: [[R:%.*]] = and i8 [[B]], 126
; CHECK-NEXT: ret i8 [[R]]
;
%a = shl i8 %x, 3
%b = lshr i8 %a, 2