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Revert "[InstCombine] try to narrow shifted bswap-of-zext" 

This reverts commit 9e9bda2e8f.

This causes a backend error when building the Linux kernel for arm64.
See https://reviews.llvm.org/D122166 for a simplified reproducer.
This commit is contained in:
Nathan Chancellor 2022-03-22 17:32:33 -07:00
parent 27bd8f9492
commit 4e0008dcbe
No known key found for this signature in database
GPG Key ID: 1D6B269171C01A96
2 changed files with 15 additions and 31 deletions
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15
llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
View File

@ -1173,21 +1173,6 @@ Instruction *InstCombinerImpl::visitLShr(BinaryOperator &I) {
MulC->logBase2() == ShAmtC)
return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, *MulC - 2));
// Try to narrow a bswap:
// (bswap (zext X)) >> C --> zext (bswap X >> C')
// In the case where the shift amount equals the bitwidth difference, the
// shift is eliminated.
if (match(Op0, m_OneUse(m_Intrinsic<Intrinsic::bswap>(
m_OneUse(m_ZExt(m_Value(X))))))) {
// TODO: If the shift amount is less than the zext, we could shift left.
unsigned WidthDiff = BitWidth - X->getType()->getScalarSizeInBits();
if (ShAmtC >= WidthDiff) {
Value *NarrowSwap = Builder.CreateUnaryIntrinsic(Intrinsic::bswap, X);
Value *NewShift = Builder.CreateLShr(NarrowSwap, ShAmtC - WidthDiff);
return new ZExtInst(NewShift, Ty);
}
}
// If the shifted-out value is known-zero, then this is an exact shift.
if (!I.isExact() &&
MaskedValueIsZero(Op0, APInt::getLowBitsSet(BitWidth, ShAmtC), 0, &I)) {

31
llvm/test/Transforms/InstCombine/lshr.ll
View File

@ -831,8 +831,9 @@ define i1 @icmp_sge(i32 %x, i32 %y) {
define i32 @narrow_bswap(i16 %x) {
; CHECK-LABEL: @narrow_bswap(
; CHECK-NEXT: [[TMP1:%.*]] = call i16 @llvm.bswap.i16(i16 [[X:%.*]])
; CHECK-NEXT: [[S:%.*]] = zext i16 [[TMP1]] to i32
; CHECK-NEXT: [[Z:%.*]] = zext i16 [[X:%.*]] to i32
; CHECK-NEXT: [[B:%.*]] = call i32 @llvm.bswap.i32(i32 [[Z]])
; CHECK-NEXT: [[S:%.*]] = lshr exact i32 [[B]], 16
; CHECK-NEXT: ret i32 [[S]]
;
%z = zext i16 %x to i32
@ -843,8 +844,9 @@ define i32 @narrow_bswap(i16 %x) {
define i128 @narrow_bswap_extra_wide(i16 %x) {
; CHECK-LABEL: @narrow_bswap_extra_wide(
; CHECK-NEXT: [[TMP1:%.*]] = call i16 @llvm.bswap.i16(i16 [[X:%.*]])
; CHECK-NEXT: [[S:%.*]] = zext i16 [[TMP1]] to i128
; CHECK-NEXT: [[Z:%.*]] = zext i16 [[X:%.*]] to i128
; CHECK-NEXT: [[B:%.*]] = call i128 @llvm.bswap.i128(i128 [[Z]])
; CHECK-NEXT: [[S:%.*]] = lshr exact i128 [[B]], 112
; CHECK-NEXT: ret i128 [[S]]
;
%z = zext i16 %x to i128
@ -853,8 +855,6 @@ define i128 @narrow_bswap_extra_wide(i16 %x) {
ret i128 %s
}
; TODO: The bswap can be narrowed followed by shl.
define i32 @narrow_bswap_undershift(i16 %x) {
; CHECK-LABEL: @narrow_bswap_undershift(
; CHECK-NEXT: [[Z:%.*]] = zext i16 [[X:%.*]] to i32
@ -870,8 +870,9 @@ define i32 @narrow_bswap_undershift(i16 %x) {
define <2 x i64> @narrow_bswap_splat(<2 x i16> %x) {
; CHECK-LABEL: @narrow_bswap_splat(
; CHECK-NEXT: [[TMP1:%.*]] = call <2 x i16> @llvm.bswap.v2i16(<2 x i16> [[X:%.*]])
; CHECK-NEXT: [[S:%.*]] = zext <2 x i16> [[TMP1]] to <2 x i64>
; CHECK-NEXT: [[Z:%.*]] = zext <2 x i16> [[X:%.*]] to <2 x i64>
; CHECK-NEXT: [[B:%.*]] = call <2 x i64> @llvm.bswap.v2i64(<2 x i64> [[Z]])
; CHECK-NEXT: [[S:%.*]] = lshr exact <2 x i64> [[B]], <i64 48, i64 48>
; CHECK-NEXT: ret <2 x i64> [[S]]
;
%z = zext <2 x i16> %x to <2 x i64>
@ -880,8 +881,6 @@ define <2 x i64> @narrow_bswap_splat(<2 x i16> %x) {
ret <2 x i64> %s
}
; TODO: poison/undef in the shift amount is ok to propagate.
define <2 x i64> @narrow_bswap_splat_poison_elt(<2 x i16> %x) {
; CHECK-LABEL: @narrow_bswap_splat_poison_elt(
; CHECK-NEXT: [[Z:%.*]] = zext <2 x i16> [[X:%.*]] to <2 x i64>
@ -897,9 +896,9 @@ define <2 x i64> @narrow_bswap_splat_poison_elt(<2 x i16> %x) {
define <2 x i64> @narrow_bswap_overshift(<2 x i32> %x) {
; CHECK-LABEL: @narrow_bswap_overshift(
; CHECK-NEXT: [[TMP1:%.*]] = call <2 x i32> @llvm.bswap.v2i32(<2 x i32> [[X:%.*]])
; CHECK-NEXT: [[TMP2:%.*]] = lshr <2 x i32> [[TMP1]], <i32 16, i32 16>
; CHECK-NEXT: [[S:%.*]] = zext <2 x i32> [[TMP2]] to <2 x i64>
; CHECK-NEXT: [[Z:%.*]] = zext <2 x i32> [[X:%.*]] to <2 x i64>
; CHECK-NEXT: [[B:%.*]] = call <2 x i64> @llvm.bswap.v2i64(<2 x i64> [[Z]])
; CHECK-NEXT: [[S:%.*]] = lshr <2 x i64> [[B]], <i64 48, i64 48>
; CHECK-NEXT: ret <2 x i64> [[S]]
;
%z = zext <2 x i32> %x to <2 x i64>
@ -910,9 +909,9 @@ define <2 x i64> @narrow_bswap_overshift(<2 x i32> %x) {
define i128 @narrow_bswap_overshift2(i96 %x) {
; CHECK-LABEL: @narrow_bswap_overshift2(
; CHECK-NEXT: [[TMP1:%.*]] = call i96 @llvm.bswap.i96(i96 [[X:%.*]])
; CHECK-NEXT: [[TMP2:%.*]] = lshr i96 [[TMP1]], 29
; CHECK-NEXT: [[S:%.*]] = zext i96 [[TMP2]] to i128
; CHECK-NEXT: [[Z:%.*]] = zext i96 [[X:%.*]] to i128
; CHECK-NEXT: [[B:%.*]] = call i128 @llvm.bswap.i128(i128 [[Z]])
; CHECK-NEXT: [[S:%.*]] = lshr i128 [[B]], 61
; CHECK-NEXT: ret i128 [[S]]
;
%z = zext i96 %x to i128