[llvm] 57590d1 - [ValueTracking] Apply the isKnownNonZero techniques in `ashr`/`lshl` to `shl` and vice-versa
Noah Goldstein via llvm-commits
llvm-commits at lists.llvm.org
Mon Apr 17 20:39:16 PDT 2023
Author: Noah Goldstein
Date: 2023-04-17T22:39:06-05:00
New Revision: 57590d1dd47bbe9aa4b79a0f93cc3ec62cc5d060
URL: https://github.com/llvm/llvm-project/commit/57590d1dd47bbe9aa4b79a0f93cc3ec62cc5d060
DIFF: https://github.com/llvm/llvm-project/commit/57590d1dd47bbe9aa4b79a0f93cc3ec62cc5d060.diff
LOG: [ValueTracking] Apply the isKnownNonZero techniques in `ashr`/`lshl` to `shl` and vice-versa
For all shifts we can apply the same two optimizations.
1) `ShiftOp(KnownVal.One, Max(KnownCnt)) != 0`
-> result is non-zero
2) If already known `Val != 0` and we only shift out zeros (based
on `Max(KnownCnt)`)
-> result is non-zero
The former exists for `shl` and the latter (for constant `Cnt`) exists
for `ashr`/`lshr`.
This patch improves the latter to use `Max(KnownCnt)` instead of
relying on a constant shift `Cnt` and applies both techniques for all
shift ops.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D148404
Added:
Modified:
llvm/lib/Analysis/ValueTracking.cpp
llvm/test/Analysis/ValueTracking/known-non-zero.ll
llvm/test/Transforms/InstCombine/ctpop-pow2.ll
Removed:
################################################################################
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 2578957277155..a5cdfdac97c3a 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2512,6 +2512,57 @@ static bool isNonZeroRecurrence(const PHINode *PN) {
}
}
+static bool isNonZeroShift(const Operator *I, const APInt &DemandedElts,
+ unsigned Depth, const Query &Q,
+ const KnownBits &KnownVal) {
+ auto ShiftOp = [&](const APInt &Lhs, const APInt &Rhs) {
+ switch (I->getOpcode()) {
+ case Instruction::Shl:
+ return Lhs.shl(Rhs);
+ case Instruction::LShr:
+ return Lhs.lshr(Rhs);
+ case Instruction::AShr:
+ return Lhs.ashr(Rhs);
+ default:
+ llvm_unreachable("Unknown Shift Opcode");
+ }
+ };
+
+ auto InvShiftOp = [&](const APInt &Lhs, const APInt &Rhs) {
+ switch (I->getOpcode()) {
+ case Instruction::Shl:
+ return Lhs.lshr(Rhs);
+ case Instruction::LShr:
+ case Instruction::AShr:
+ return Lhs.shl(Rhs);
+ default:
+ llvm_unreachable("Unknown Shift Opcode");
+ }
+ };
+
+ if (KnownVal.isUnknown())
+ return false;
+
+ KnownBits KnownCnt =
+ computeKnownBits(I->getOperand(1), DemandedElts, Depth, Q);
+ APInt MaxShift = KnownCnt.getMaxValue();
+ unsigned NumBits = KnownVal.getBitWidth();
+ if (MaxShift.uge(NumBits))
+ return false;
+
+ if (!ShiftOp(KnownVal.One, MaxShift).isZero())
+ return true;
+
+ // If all of the bits shifted out are known to be zero, and Val is known
+ // non-zero then at least one non-zero bit must remain.
+ if (InvShiftOp(KnownVal.Zero, NumBits - MaxShift)
+ .eq(InvShiftOp(APInt::getAllOnes(NumBits), NumBits - MaxShift)) &&
+ isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q))
+ return true;
+
+ return false;
+}
+
/// Return true if the given value is known to be non-zero when defined. For
/// vectors, return true if every demanded element is known to be non-zero when
/// defined. For pointers, if the context instruction and dominator tree are
@@ -2682,16 +2733,7 @@ bool isKnownNonZero(const Value *V, const APInt &DemandedElts, unsigned Depth,
if (Known.One[0])
return true;
- if (!Known.isUnknown()) {
- KnownBits KnownCnt =
- computeKnownBits(I->getOperand(1), DemandedElts, Depth, Q);
-
- if (KnownCnt.getMaxValue().ult(Known.getBitWidth()) &&
- !Known.One.shl(KnownCnt.getMaxValue()).isZero())
- return true;
- }
-
- break;
+ return isNonZeroShift(I, DemandedElts, Depth, Q, Known);
}
case Instruction::LShr:
case Instruction::AShr: {
@@ -2707,19 +2749,7 @@ bool isKnownNonZero(const Value *V, const APInt &DemandedElts, unsigned Depth,
if (Known.isNegative())
return true;
- // If the shifter operand is a constant, and all of the bits shifted
- // out are known to be zero, and X is known non-zero then at least one
- // non-zero bit must remain.
- if (ConstantInt *Shift = dyn_cast<ConstantInt>(I->getOperand(1))) {
- auto ShiftVal = Shift->getLimitedValue(BitWidth - 1);
- // Is there a known one in the portion not shifted out?
- if (Known.countMaxLeadingZeros() < BitWidth - ShiftVal)
- return true;
- // Are all the bits to be shifted out known zero?
- if (Known.countMinTrailingZeros() >= ShiftVal)
- return isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q);
- }
- break;
+ return isNonZeroShift(I, DemandedElts, Depth, Q, Known);
}
case Instruction::UDiv:
case Instruction::SDiv:
diff --git a/llvm/test/Analysis/ValueTracking/known-non-zero.ll b/llvm/test/Analysis/ValueTracking/known-non-zero.ll
index 346879582e191..37e0b11c98af1 100644
--- a/llvm/test/Analysis/ValueTracking/known-non-zero.ll
+++ b/llvm/test/Analysis/ValueTracking/known-non-zero.ll
@@ -261,10 +261,7 @@ define i1 @lshr_nz_bounded_cnt(i32 %cnt, i32 %y) {
; CHECK-LABEL: @lshr_nz_bounded_cnt(
; CHECK-NEXT: [[CNT_ULT4:%.*]] = icmp ult i32 [[CNT:%.*]], 4
; CHECK-NEXT: call void @llvm.assume(i1 [[CNT_ULT4]])
-; CHECK-NEXT: [[VAL:%.*]] = or i32 [[Y:%.*]], 90
-; CHECK-NEXT: [[SHL:%.*]] = lshr i32 [[VAL]], [[CNT]]
-; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[SHL]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%cnt_ult4 = icmp ult i32 %cnt, 4
call void @llvm.assume(i1 %cnt_ult4)
@@ -276,11 +273,7 @@ define i1 @lshr_nz_bounded_cnt(i32 %cnt, i32 %y) {
define <2 x i1> @ashr_nz_bounded_cnt_vec(<2 x i32> %x, <2 x i32> %y) {
; CHECK-LABEL: @ashr_nz_bounded_cnt_vec(
-; CHECK-NEXT: [[CNT:%.*]] = and <2 x i32> [[X:%.*]], <i32 16, i32 24>
-; CHECK-NEXT: [[VAL:%.*]] = or <2 x i32> [[Y:%.*]], <i32 402784272, i32 268697601>
-; CHECK-NEXT: [[SHL:%.*]] = ashr <2 x i32> [[VAL]], [[CNT]]
-; CHECK-NEXT: [[R:%.*]] = icmp eq <2 x i32> [[SHL]], zeroinitializer
-; CHECK-NEXT: ret <2 x i1> [[R]]
+; CHECK-NEXT: ret <2 x i1> zeroinitializer
;
%cnt = and <2 x i32> %x, <i32 16, i32 24>
%val = or <2 x i32> %y, <i32 402784272, i32 268697601>
@@ -332,9 +325,7 @@ define i1 @lshr_nonzero_and_shift_out_zeros(i32 %cnt, i32 %y) {
; CHECK-NEXT: [[VAL:%.*]] = and i32 [[Y:%.*]], -131072
; CHECK-NEXT: [[VAL_NZ:%.*]] = icmp ne i32 [[VAL]], 0
; CHECK-NEXT: call void @llvm.assume(i1 [[VAL_NZ]])
-; CHECK-NEXT: [[SHL:%.*]] = lshr i32 [[VAL]], [[CNT]]
-; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[SHL]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%cnt_ult = icmp ult i32 %cnt, 4
call void @llvm.assume(i1 %cnt_ult)
@@ -352,13 +343,10 @@ define i1 @lshr_nonzero_and_shift_out_zeros(i32 %cnt, i32 %y) {
define i1 @ashr_nonzero_and_shift_out_zeros(i32 %ccnt, i32 %y) {
; CHECK-LABEL: @ashr_nonzero_and_shift_out_zeros(
-; CHECK-NEXT: [[CNT:%.*]] = and i32 [[CCNT:%.*]], 7
; CHECK-NEXT: [[VAL:%.*]] = and i32 [[Y:%.*]], -131072
; CHECK-NEXT: [[VAL_NZ:%.*]] = icmp ne i32 [[VAL]], 0
; CHECK-NEXT: call void @llvm.assume(i1 [[VAL_NZ]])
-; CHECK-NEXT: [[SHL:%.*]] = ashr i32 [[VAL]], [[CNT]]
-; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[SHL]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%cnt = and i32 %ccnt, 7
%val = and i32 %y, -131072
@@ -372,13 +360,10 @@ define i1 @ashr_nonzero_and_shift_out_zeros(i32 %ccnt, i32 %y) {
define i1 @shl_nonzero_and_shift_out_zeros(i32 %ccnt, i32 %y) {
; CHECK-LABEL: @shl_nonzero_and_shift_out_zeros(
-; CHECK-NEXT: [[CNT:%.*]] = and i32 [[CCNT:%.*]], 6
; CHECK-NEXT: [[VAL:%.*]] = and i32 [[Y:%.*]], 131071
; CHECK-NEXT: [[VAL_NZ:%.*]] = icmp ne i32 [[VAL]], 0
; CHECK-NEXT: call void @llvm.assume(i1 [[VAL_NZ]])
-; CHECK-NEXT: [[SHL:%.*]] = shl i32 [[VAL]], [[CNT]]
-; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[SHL]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%cnt = and i32 %ccnt, 6
%val = and i32 %y, 131071
diff --git a/llvm/test/Transforms/InstCombine/ctpop-pow2.ll b/llvm/test/Transforms/InstCombine/ctpop-pow2.ll
index b73aff5287446..f6757c2ff33cf 100644
--- a/llvm/test/Transforms/InstCombine/ctpop-pow2.ll
+++ b/llvm/test/Transforms/InstCombine/ctpop-pow2.ll
@@ -116,11 +116,7 @@ define <2 x i32> @ctpop_lshr_intmin_intmin_plus1_vec_nz(<2 x i32> %x) {
define <2 x i32> @ctpop_shl2_1_vec_nz(<2 x i32> %x) {
; CHECK-LABEL: @ctpop_shl2_1_vec_nz(
-; CHECK-NEXT: [[AND:%.*]] = and <2 x i32> [[X:%.*]], <i32 15, i32 15>
-; CHECK-NEXT: [[SHL:%.*]] = shl <2 x i32> <i32 2, i32 1>, [[AND]]
-; CHECK-NEXT: [[TMP1:%.*]] = icmp ne <2 x i32> [[SHL]], zeroinitializer
-; CHECK-NEXT: [[CNT:%.*]] = zext <2 x i1> [[TMP1]] to <2 x i32>
-; CHECK-NEXT: ret <2 x i32> [[CNT]]
+; CHECK-NEXT: ret <2 x i32> <i32 1, i32 1>
;
%and = and <2 x i32> %x, <i32 15 ,i32 15>
%shl = shl <2 x i32> <i32 2 ,i32 1>, %and
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