[llvm] 9e9bda2 - [InstCombine] try to narrow shifted bswap-of-zext
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Tue Mar 22 05:29:49 PDT 2022
Author: Sanjay Patel
Date: 2022-03-22T08:22:30-04:00
New Revision: 9e9bda2e8f5b88715bad767a4b7740df32b040d2
URL: https://github.com/llvm/llvm-project/commit/9e9bda2e8f5b88715bad767a4b7740df32b040d2
DIFF: https://github.com/llvm/llvm-project/commit/9e9bda2e8f5b88715bad767a4b7740df32b040d2.diff
LOG: [InstCombine] try to narrow shifted bswap-of-zext
This is the IR counterpart to 370ebc9d9a573d6
which provided a bswap narrowing fix for issue #53867.
Here we can be more general (although I'm not sure yet
what would happen for illegal types in codegen - too
rare to worry about?):
https://alive2.llvm.org/ce/z/3-CPfo
This will be more effective if we have moved the shift
after the bswap as proposed in D122010, but it is
independent of that patch.
Differential Revision: https://reviews.llvm.org/D122166
Added:
Modified:
llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
llvm/test/Transforms/InstCombine/lshr.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index 03214118a2cf7..403979b4a6a39 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -1173,6 +1173,21 @@ 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
diff erence, 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)) {
diff --git a/llvm/test/Transforms/InstCombine/lshr.ll b/llvm/test/Transforms/InstCombine/lshr.ll
index 175430189ce12..a46f3f460f5e8 100644
--- a/llvm/test/Transforms/InstCombine/lshr.ll
+++ b/llvm/test/Transforms/InstCombine/lshr.ll
@@ -831,9 +831,8 @@ define i1 @icmp_sge(i32 %x, i32 %y) {
define i32 @narrow_bswap(i16 %x) {
; CHECK-LABEL: @narrow_bswap(
-; 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: [[TMP1:%.*]] = call i16 @llvm.bswap.i16(i16 [[X:%.*]])
+; CHECK-NEXT: [[S:%.*]] = zext i16 [[TMP1]] to i32
; CHECK-NEXT: ret i32 [[S]]
;
%z = zext i16 %x to i32
@@ -844,9 +843,8 @@ define i32 @narrow_bswap(i16 %x) {
define i128 @narrow_bswap_extra_wide(i16 %x) {
; CHECK-LABEL: @narrow_bswap_extra_wide(
-; 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: [[TMP1:%.*]] = call i16 @llvm.bswap.i16(i16 [[X:%.*]])
+; CHECK-NEXT: [[S:%.*]] = zext i16 [[TMP1]] to i128
; CHECK-NEXT: ret i128 [[S]]
;
%z = zext i16 %x to i128
@@ -855,6 +853,8 @@ 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
@@ -870,9 +870,8 @@ 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: [[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: [[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: ret <2 x i64> [[S]]
;
%z = zext <2 x i16> %x to <2 x i64>
@@ -881,6 +880,8 @@ 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>
@@ -896,9 +897,9 @@ 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: [[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: [[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: ret <2 x i64> [[S]]
;
%z = zext <2 x i32> %x to <2 x i64>
@@ -909,9 +910,9 @@ 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: [[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: [[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: ret i128 [[S]]
;
%z = zext i96 %x to i128
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