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[InstCombine] fold mask op into casted shift (PR46013) 

https://rise4fun.com/Alive/Qply8

  Pre: C2 == (-1 u>> zext(C1))
  %a = ashr %x, C1
  %s = sext %a to i16
  %r = and i16 %s, C2
    =>
  %s2 = sext %x to i16
  %r = lshr i16 %s2, zext(C1)

https://bugs.llvm.org/show_bug.cgi?id=46013
This commit is contained in:
Sanjay Patel 2020-06-07 09:03:45 -04:00
parent c6719d0b47
commit 2552f65183
2 changed files with 53 additions and 9 deletions
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12
llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
View File

@ -1848,7 +1848,17 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
return BinaryOperator::Create(BinOp, NewLHS, Y);
}
}
const APInt *ShiftC;
if (match(Op0, m_OneUse(m_SExt(m_AShr(m_Value(X), m_APInt(ShiftC)))))) {
unsigned Width = I.getType()->getScalarSizeInBits();
if (*C == APInt::getLowBitsSet(Width, Width - ShiftC->getZExtValue())) {
// We are clearing high bits that were potentially set by sext+ashr:
// and (sext (ashr X, ShiftC)), C --> lshr (sext X), ShiftC
Value *Sext = Builder.CreateSExt(X, I.getType());
Constant *ShAmtC = ConstantInt::get(I.getType(), ShiftC->zext(Width));
return BinaryOperator::CreateLShr(Sext, ShAmtC);
}
}
}
if (ConstantInt *AndRHS = dyn_cast<ConstantInt>(Op1)) {

50
llvm/test/Transforms/InstCombine/and.ll
View File

@ -847,9 +847,8 @@ define i1 @andn_or_cmp_4(i32 %a, i32 %b, i32 %c) {
define i32 @lowbitmask_casted_shift(i8 %x) {
; CHECK-LABEL: @lowbitmask_casted_shift(
; CHECK-NEXT: [[A:%.*]] = ashr i8 [[X:%.*]], 1
; CHECK-NEXT: [[S:%.*]] = sext i8 [[A]] to i32
; CHECK-NEXT: [[R:%.*]] = and i32 [[S]], 2147483647
; CHECK-NEXT: [[TMP1:%.*]] = sext i8 [[X:%.*]] to i32
; CHECK-NEXT: [[R:%.*]] = lshr i32 [[TMP1]], 1
; CHECK-NEXT: ret i32 [[R]]
;
%a = ashr i8 %x, 1
@ -858,12 +857,44 @@ define i32 @lowbitmask_casted_shift(i8 %x) {
ret i32 %r
}
; Negative test - mask constant is too big.
define i32 @lowbitmask_casted_shift_wrong_mask1(i8 %x) {
; CHECK-LABEL: @lowbitmask_casted_shift_wrong_mask1(
; CHECK-NEXT: [[A:%.*]] = ashr i8 [[X:%.*]], 2
; CHECK-NEXT: [[S:%.*]] = sext i8 [[A]] to i32
; CHECK-NEXT: [[R:%.*]] = and i32 [[S]], 2147483647
; CHECK-NEXT: ret i32 [[R]]
;
%a = ashr i8 %x, 2
%s = sext i8 %a to i32
%r = and i32 %s, 2147483647 ; 0x7fffffff
ret i32 %r
}
; Negative test - mask constant is too small.
define i32 @lowbitmask_casted_shift_wrong_mask2(i8 %x) {
; CHECK-LABEL: @lowbitmask_casted_shift_wrong_mask2(
; CHECK-NEXT: [[A:%.*]] = ashr i8 [[X:%.*]], 2
; CHECK-NEXT: [[S:%.*]] = sext i8 [[A]] to i32
; CHECK-NEXT: [[R:%.*]] = and i32 [[S]], 536870911
; CHECK-NEXT: ret i32 [[R]]
;
%a = ashr i8 %x, 2
%s = sext i8 %a to i32
%r = and i32 %s, 536870911 ; 0x1fffffff
ret i32 %r
}
; Extra use of shift is ok.
define i32 @lowbitmask_casted_shift_use1(i8 %x) {
; CHECK-LABEL: @lowbitmask_casted_shift_use1(
; CHECK-NEXT: [[A:%.*]] = ashr i8 [[X:%.*]], 3
; CHECK-NEXT: call void @use8(i8 [[A]])
; CHECK-NEXT: [[S:%.*]] = sext i8 [[A]] to i32
; CHECK-NEXT: [[R:%.*]] = and i32 [[S]], 536870911
; CHECK-NEXT: [[TMP1:%.*]] = sext i8 [[X]] to i32
; CHECK-NEXT: [[R:%.*]] = lshr i32 [[TMP1]], 3
; CHECK-NEXT: ret i32 [[R]]
;
%a = ashr i8 %x, 3
@ -873,6 +904,8 @@ define i32 @lowbitmask_casted_shift_use1(i8 %x) {
ret i32 %r
}
; Negative test - extra use of sext requires more instructions.
define i32 @lowbitmask_casted_shift_use2(i8 %x) {
; CHECK-LABEL: @lowbitmask_casted_shift_use2(
; CHECK-NEXT: [[A:%.*]] = ashr i8 [[X:%.*]], 3
@ -888,11 +921,12 @@ define i32 @lowbitmask_casted_shift_use2(i8 %x) {
ret i32 %r
}
; Vectors/weird types are ok.
define <2 x i59> @lowbitmask_casted_shift_vec_splat(<2 x i47> %x) {
; CHECK-LABEL: @lowbitmask_casted_shift_vec_splat(
; CHECK-NEXT: [[A:%.*]] = ashr <2 x i47> [[X:%.*]], <i47 5, i47 5>
; CHECK-NEXT: [[S:%.*]] = sext <2 x i47> [[A]] to <2 x i59>
; CHECK-NEXT: [[R:%.*]] = and <2 x i59> [[S]], <i59 18014398509481983, i59 18014398509481983>
; CHECK-NEXT: [[TMP1:%.*]] = sext <2 x i47> [[X:%.*]] to <2 x i59>
; CHECK-NEXT: [[R:%.*]] = lshr <2 x i59> [[TMP1]], <i59 5, i59 5>
; CHECK-NEXT: ret <2 x i59> [[R]]
;
%a = ashr <2 x i47> %x, <i47 5, i47 5>