[ValueTracking] Support dominating known bits condition in and/or #74728
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@llvm/pr-subscribers-llvm-analysis @llvm/pr-subscribers-llvm-transforms Author: Nikita Popov (nikic) ChangesThis extends computeKnownBits() support for dominating conditions to also handle and/or conditions. We'll look through either and or or depending on which edge we're considering. This change is mainly for the sake of completeness, so we don't start missing optimizations if SimplifyCFG decides to merge some branches. Full diff: https://github.com/llvm/llvm-project/pull/74728.diff 4 Files Affected:
diff --git a/llvm/lib/Analysis/DomConditionCache.cpp b/llvm/lib/Analysis/DomConditionCache.cpp
index 351881fe9e1f9..4a1eea57ed5bf 100644
--- a/llvm/lib/Analysis/DomConditionCache.cpp
+++ b/llvm/lib/Analysis/DomConditionCache.cpp
@@ -34,24 +34,40 @@ static void findAffectedValues(Value *Cond,
}
};
- ICmpInst::Predicate Pred;
- Value *A;
- Constant *C;
- if (match(Cond, m_ICmp(Pred, m_Value(A), m_Constant(C)))) {
- AddAffected(A);
+ bool TopLevelIsAnd = match(Cond, m_LogicalAnd());
+ SmallVector<Value *, 8> Worklist;
+ SmallPtrSet<Value *, 8> Visited;
+ Worklist.push_back(Cond);
+ while (!Worklist.empty()) {
+ Value *V = Worklist.pop_back_val();
+ if (!Visited.insert(V).second)
+ continue;
- if (ICmpInst::isEquality(Pred)) {
- Value *X;
- // (X & C) or (X | C) or (X ^ C).
- // (X << C) or (X >>_s C) or (X >>_u C).
- if (match(A, m_BitwiseLogic(m_Value(X), m_ConstantInt())) ||
- match(A, m_Shift(m_Value(X), m_ConstantInt())))
- AddAffected(X);
- } else {
- Value *X;
- // Handle (A + C1) u< C2, which is the canonical form of A > C3 && A < C4.
- if (match(A, m_Add(m_Value(X), m_ConstantInt())))
- AddAffected(X);
+ ICmpInst::Predicate Pred;
+ Value *A, *B;
+ Constant *C;
+ // Only recurse into and/or if it matches the top-level and/or type.
+ if (TopLevelIsAnd ? match(V, m_LogicalAnd(m_Value(A), m_Value(B)))
+ : match(V, m_LogicalOr(m_Value(A), m_Value(B)))) {
+ Worklist.push_back(A);
+ Worklist.push_back(B);
+ } else if (match(V, m_ICmp(Pred, m_Value(A), m_Constant(C)))) {
+ AddAffected(A);
+
+ if (ICmpInst::isEquality(Pred)) {
+ Value *X;
+ // (X & C) or (X | C) or (X ^ C).
+ // (X << C) or (X >>_s C) or (X >>_u C).
+ if (match(A, m_BitwiseLogic(m_Value(X), m_ConstantInt())) ||
+ match(A, m_Shift(m_Value(X), m_ConstantInt())))
+ AddAffected(X);
+ } else {
+ Value *X;
+ // Handle (A + C1) u< C2, which is the canonical form of
+ // A > C3 && A < C4.
+ if (match(A, m_Add(m_Value(X), m_ConstantInt())))
+ AddAffected(X);
+ }
}
}
}
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 2c52107dab23b..7db141a0ea758 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -705,28 +705,40 @@ static void computeKnownBitsFromCmp(const Value *V, CmpInst::Predicate Pred,
}
}
+static void computeKnownBitsFromCond(const Value *V, Value *Cond,
+ KnownBits &Known, unsigned Depth,
+ const SimplifyQuery &SQ, bool Invert) {
+ Value *A, *B;
+ if (Depth < MaxAnalysisRecursionDepth &&
+ (Invert ? match(Cond, m_LogicalOr(m_Value(A), m_Value(B)))
+ : match(Cond, m_LogicalAnd(m_Value(A), m_Value(B))))) {
+ computeKnownBitsFromCond(V, A, Known, Depth + 1, SQ, Invert);
+ computeKnownBitsFromCond(V, B, Known, Depth + 1, SQ, Invert);
+ }
+
+ if (auto *Cmp = dyn_cast<ICmpInst>(Cond))
+ computeKnownBitsFromCmp(
+ V, Invert ? Cmp->getInversePredicate() : Cmp->getPredicate(),
+ Cmp->getOperand(0), Cmp->getOperand(1), Known, Depth, SQ);
+}
+
void llvm::computeKnownBitsFromContext(const Value *V, KnownBits &Known,
- unsigned Depth, const SimplifyQuery &Q) {
+ unsigned Depth, const SimplifyQuery &Q) {
if (!Q.CxtI)
return;
if (Q.DC && Q.DT) {
// Handle dominating conditions.
for (BranchInst *BI : Q.DC->conditionsFor(V)) {
- auto *Cmp = dyn_cast<ICmpInst>(BI->getCondition());
- if (!Cmp)
- continue;
-
BasicBlockEdge Edge0(BI->getParent(), BI->getSuccessor(0));
if (Q.DT->dominates(Edge0, Q.CxtI->getParent()))
- computeKnownBitsFromCmp(V, Cmp->getPredicate(), Cmp->getOperand(0),
- Cmp->getOperand(1), Known, Depth, Q);
+ computeKnownBitsFromCond(V, BI->getCondition(), Known, Depth, Q,
+ /*Invert*/ false);
BasicBlockEdge Edge1(BI->getParent(), BI->getSuccessor(1));
if (Q.DT->dominates(Edge1, Q.CxtI->getParent()))
- computeKnownBitsFromCmp(V, Cmp->getInversePredicate(),
- Cmp->getOperand(0), Cmp->getOperand(1), Known,
- Depth, Q);
+ computeKnownBitsFromCond(V, BI->getCondition(), Known, Depth, Q,
+ /*Invert*/ true);
}
if (Known.hasConflict())
diff --git a/llvm/test/Transforms/InstCombine/known-bits.ll b/llvm/test/Transforms/InstCombine/known-bits.ll
index e346330aa5b1e..246579cc4cd0c 100644
--- a/llvm/test/Transforms/InstCombine/known-bits.ll
+++ b/llvm/test/Transforms/InstCombine/known-bits.ll
@@ -105,8 +105,7 @@ define i8 @test_cond_and(i8 %x, i1 %c) {
; CHECK-NEXT: [[COND:%.*]] = and i1 [[CMP]], [[C:%.*]]
; CHECK-NEXT: br i1 [[COND]], label [[IF:%.*]], label [[EXIT:%.*]]
; CHECK: if:
-; CHECK-NEXT: [[OR1:%.*]] = or i8 [[X]], -4
-; CHECK-NEXT: ret i8 [[OR1]]
+; CHECK-NEXT: ret i8 -4
; CHECK: exit:
; CHECK-NEXT: [[OR2:%.*]] = or i8 [[X]], -4
; CHECK-NEXT: ret i8 [[OR2]]
@@ -133,8 +132,7 @@ define i8 @test_cond_and_commuted(i8 %x, i1 %c1, i1 %c2) {
; CHECK-NEXT: [[COND:%.*]] = and i1 [[C3]], [[CMP]]
; CHECK-NEXT: br i1 [[COND]], label [[IF:%.*]], label [[EXIT:%.*]]
; CHECK: if:
-; CHECK-NEXT: [[OR1:%.*]] = or i8 [[X]], -4
-; CHECK-NEXT: ret i8 [[OR1]]
+; CHECK-NEXT: ret i8 -4
; CHECK: exit:
; CHECK-NEXT: [[OR2:%.*]] = or i8 [[X]], -4
; CHECK-NEXT: ret i8 [[OR2]]
@@ -161,8 +159,7 @@ define i8 @test_cond_logical_and(i8 %x, i1 %c) {
; CHECK-NEXT: [[COND:%.*]] = select i1 [[CMP]], i1 [[C:%.*]], i1 false
; CHECK-NEXT: br i1 [[COND]], label [[IF:%.*]], label [[EXIT:%.*]]
; CHECK: if:
-; CHECK-NEXT: [[OR1:%.*]] = or i8 [[X]], -4
-; CHECK-NEXT: ret i8 [[OR1]]
+; CHECK-NEXT: ret i8 -4
; CHECK: exit:
; CHECK-NEXT: [[OR2:%.*]] = or i8 [[X]], -4
; CHECK-NEXT: ret i8 [[OR2]]
@@ -218,8 +215,7 @@ define i8 @test_cond_inv_or(i8 %x, i1 %c) {
; CHECK-NEXT: [[OR1:%.*]] = or i8 [[X]], -4
; CHECK-NEXT: ret i8 [[OR1]]
; CHECK: exit:
-; CHECK-NEXT: [[OR2:%.*]] = or i8 [[X]], -4
-; CHECK-NEXT: ret i8 [[OR2]]
+; CHECK-NEXT: ret i8 -4
;
%and = and i8 %x, 3
%cmp = icmp ne i8 %and, 0
@@ -242,8 +238,7 @@ define i8 @test_cond_inv_logical_or(i8 %x, i1 %c) {
; CHECK-NEXT: [[COND:%.*]] = select i1 [[CMP_NOT]], i1 [[C:%.*]], i1 false
; CHECK-NEXT: br i1 [[COND]], label [[IF:%.*]], label [[EXIT:%.*]]
; CHECK: if:
-; CHECK-NEXT: [[OR1:%.*]] = or i8 [[X]], -4
-; CHECK-NEXT: ret i8 [[OR1]]
+; CHECK-NEXT: ret i8 -4
; CHECK: exit:
; CHECK-NEXT: [[OR2:%.*]] = or i8 [[X]], -4
; CHECK-NEXT: ret i8 [[OR2]]
diff --git a/llvm/test/Transforms/LoopVectorize/induction.ll b/llvm/test/Transforms/LoopVectorize/induction.ll
index a8cfac64258e8..9e7648b29cfa5 100644
--- a/llvm/test/Transforms/LoopVectorize/induction.ll
+++ b/llvm/test/Transforms/LoopVectorize/induction.ll
@@ -3525,10 +3525,10 @@ define void @wrappingindvars1(i8 %t, i32 %len, ptr %A) {
; IND-NEXT: [[TMP9:%.*]] = or i1 [[TMP3]], [[TMP8]]
; IND-NEXT: br i1 [[TMP9]], label [[SCALAR_PH]], label [[VECTOR_PH:%.*]]
; IND: vector.ph:
-; IND-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], -2
+; IND-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], 510
; IND-NEXT: [[DOTCAST:%.*]] = trunc i32 [[N_VEC]] to i8
; IND-NEXT: [[IND_END:%.*]] = add i8 [[DOTCAST]], [[T]]
-; IND-NEXT: [[IND_END2:%.*]] = add i32 [[N_VEC]], [[EXT]]
+; IND-NEXT: [[IND_END2:%.*]] = add nuw nsw i32 [[N_VEC]], [[EXT]]
; IND-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <2 x i32> poison, i32 [[EXT]], i64 0
; IND-NEXT: [[DOTSPLAT:%.*]] = shufflevector <2 x i32> [[DOTSPLATINSERT]], <2 x i32> poison, <2 x i32> zeroinitializer
; IND-NEXT: [[INDUCTION:%.*]] = add nuw nsw <2 x i32> [[DOTSPLAT]], <i32 0, i32 1>
@@ -3591,10 +3591,10 @@ define void @wrappingindvars1(i8 %t, i32 %len, ptr %A) {
; UNROLL-NEXT: [[TMP9:%.*]] = or i1 [[TMP3]], [[TMP8]]
; UNROLL-NEXT: br i1 [[TMP9]], label [[SCALAR_PH]], label [[VECTOR_PH:%.*]]
; UNROLL: vector.ph:
-; UNROLL-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], -4
+; UNROLL-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], 508
; UNROLL-NEXT: [[DOTCAST:%.*]] = trunc i32 [[N_VEC]] to i8
; UNROLL-NEXT: [[IND_END:%.*]] = add i8 [[DOTCAST]], [[T]]
-; UNROLL-NEXT: [[IND_END2:%.*]] = add i32 [[N_VEC]], [[EXT]]
+; UNROLL-NEXT: [[IND_END2:%.*]] = add nuw nsw i32 [[N_VEC]], [[EXT]]
; UNROLL-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <2 x i32> poison, i32 [[EXT]], i64 0
; UNROLL-NEXT: [[DOTSPLAT:%.*]] = shufflevector <2 x i32> [[DOTSPLATINSERT]], <2 x i32> poison, <2 x i32> zeroinitializer
; UNROLL-NEXT: [[INDUCTION:%.*]] = add nuw nsw <2 x i32> [[DOTSPLAT]], <i32 0, i32 1>
@@ -3735,10 +3735,10 @@ define void @wrappingindvars1(i8 %t, i32 %len, ptr %A) {
; INTERLEAVE-NEXT: [[TMP9:%.*]] = or i1 [[TMP3]], [[TMP8]]
; INTERLEAVE-NEXT: br i1 [[TMP9]], label [[SCALAR_PH]], label [[VECTOR_PH:%.*]]
; INTERLEAVE: vector.ph:
-; INTERLEAVE-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], -8
+; INTERLEAVE-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], 504
; INTERLEAVE-NEXT: [[DOTCAST:%.*]] = trunc i32 [[N_VEC]] to i8
; INTERLEAVE-NEXT: [[IND_END:%.*]] = add i8 [[DOTCAST]], [[T]]
-; INTERLEAVE-NEXT: [[IND_END2:%.*]] = add i32 [[N_VEC]], [[EXT]]
+; INTERLEAVE-NEXT: [[IND_END2:%.*]] = add nuw nsw i32 [[N_VEC]], [[EXT]]
; INTERLEAVE-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <4 x i32> poison, i32 [[EXT]], i64 0
; INTERLEAVE-NEXT: [[DOTSPLAT:%.*]] = shufflevector <4 x i32> [[DOTSPLATINSERT]], <4 x i32> poison, <4 x i32> zeroinitializer
; INTERLEAVE-NEXT: [[INDUCTION:%.*]] = add nuw nsw <4 x i32> [[DOTSPLAT]], <i32 0, i32 1, i32 2, i32 3>
@@ -3909,11 +3909,11 @@ define void @wrappingindvars2(i8 %t, i32 %len, ptr %A) {
; IND-NEXT: [[TMP9:%.*]] = or i1 [[TMP3]], [[TMP8]]
; IND-NEXT: br i1 [[TMP9]], label [[SCALAR_PH]], label [[VECTOR_PH:%.*]]
; IND: vector.ph:
-; IND-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], -2
+; IND-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], 510
; IND-NEXT: [[DOTCAST:%.*]] = trunc i32 [[N_VEC]] to i8
; IND-NEXT: [[IND_END:%.*]] = add i8 [[DOTCAST]], [[T]]
-; IND-NEXT: [[EXT_MUL5:%.*]] = add i32 [[N_VEC]], [[EXT]]
-; IND-NEXT: [[IND_END1:%.*]] = shl i32 [[EXT_MUL5]], 2
+; IND-NEXT: [[EXT_MUL5:%.*]] = add nuw nsw i32 [[N_VEC]], [[EXT]]
+; IND-NEXT: [[IND_END1:%.*]] = shl nuw nsw i32 [[EXT_MUL5]], 2
; IND-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <2 x i32> poison, i32 [[EXT_MUL]], i64 0
; IND-NEXT: [[DOTSPLAT:%.*]] = shufflevector <2 x i32> [[DOTSPLATINSERT]], <2 x i32> poison, <2 x i32> zeroinitializer
; IND-NEXT: [[INDUCTION:%.*]] = add nuw nsw <2 x i32> [[DOTSPLAT]], <i32 0, i32 4>
@@ -3978,11 +3978,11 @@ define void @wrappingindvars2(i8 %t, i32 %len, ptr %A) {
; UNROLL-NEXT: [[TMP9:%.*]] = or i1 [[TMP3]], [[TMP8]]
; UNROLL-NEXT: br i1 [[TMP9]], label [[SCALAR_PH]], label [[VECTOR_PH:%.*]]
; UNROLL: vector.ph:
-; UNROLL-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], -4
+; UNROLL-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], 508
; UNROLL-NEXT: [[DOTCAST:%.*]] = trunc i32 [[N_VEC]] to i8
; UNROLL-NEXT: [[IND_END:%.*]] = add i8 [[DOTCAST]], [[T]]
-; UNROLL-NEXT: [[EXT_MUL6:%.*]] = add i32 [[N_VEC]], [[EXT]]
-; UNROLL-NEXT: [[IND_END1:%.*]] = shl i32 [[EXT_MUL6]], 2
+; UNROLL-NEXT: [[EXT_MUL6:%.*]] = add nuw nsw i32 [[N_VEC]], [[EXT]]
+; UNROLL-NEXT: [[IND_END1:%.*]] = shl nuw nsw i32 [[EXT_MUL6]], 2
; UNROLL-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <2 x i32> poison, i32 [[EXT_MUL]], i64 0
; UNROLL-NEXT: [[DOTSPLAT:%.*]] = shufflevector <2 x i32> [[DOTSPLATINSERT]], <2 x i32> poison, <2 x i32> zeroinitializer
; UNROLL-NEXT: [[INDUCTION:%.*]] = add nuw nsw <2 x i32> [[DOTSPLAT]], <i32 0, i32 4>
@@ -4128,11 +4128,11 @@ define void @wrappingindvars2(i8 %t, i32 %len, ptr %A) {
; INTERLEAVE-NEXT: [[TMP9:%.*]] = or i1 [[TMP3]], [[TMP8]]
; INTERLEAVE-NEXT: br i1 [[TMP9]], label [[SCALAR_PH]], label [[VECTOR_PH:%.*]]
; INTERLEAVE: vector.ph:
-; INTERLEAVE-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], -8
+; INTERLEAVE-NEXT: [[N_VEC:%.*]] = and i32 [[TMP0]], 504
; INTERLEAVE-NEXT: [[DOTCAST:%.*]] = trunc i32 [[N_VEC]] to i8
; INTERLEAVE-NEXT: [[IND_END:%.*]] = add i8 [[DOTCAST]], [[T]]
-; INTERLEAVE-NEXT: [[EXT_MUL6:%.*]] = add i32 [[N_VEC]], [[EXT]]
-; INTERLEAVE-NEXT: [[IND_END1:%.*]] = shl i32 [[EXT_MUL6]], 2
+; INTERLEAVE-NEXT: [[EXT_MUL6:%.*]] = add nuw nsw i32 [[N_VEC]], [[EXT]]
+; INTERLEAVE-NEXT: [[IND_END1:%.*]] = shl nuw nsw i32 [[EXT_MUL6]], 2
; INTERLEAVE-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <4 x i32> poison, i32 [[EXT_MUL]], i64 0
; INTERLEAVE-NEXT: [[DOTSPLAT:%.*]] = shufflevector <4 x i32> [[DOTSPLATINSERT]], <4 x i32> poison, <4 x i32> zeroinitializer
; INTERLEAVE-NEXT: [[INDUCTION:%.*]] = add nuw nsw <4 x i32> [[DOTSPLAT]], <i32 0, i32 4, i32 8, i32 12>
|
dtcxzyw
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goldsteinn
reviewed
Dec 9, 2023
goldsteinn
reviewed
Dec 9, 2023
|
@nikic Could you please have a look at dtcxzyw/llvm-opt-benchmark#6? |
|
Ping. |
|
@dtcxzyw It's been a while, but IIRC I addressed most of the "interesting" regressions. The main one left is some sub-optimality in IV widening (we don't make good use of the fact that top bits are zero for the widened LCSSA phi node), which would ideally be solved by introducing trunc nuw/nsw, though I guess we could also add special support for it during widening. |
dtcxzyw
approved these changes
Feb 5, 2024
| SmallVector<Value *, 8> Worklist; | ||
| SmallPtrSet<Value *, 8> Visited; | ||
| Worklist.push_back(Cond); | ||
| while (!Worklist.empty()) { |
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What is the compile-time impact after this patch?
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| @@ -705,28 +705,40 @@ static void computeKnownBitsFromCmp(const Value *V, CmpInst::Predicate Pred, | |||
| } | |||
| } | |||
|
|
|||
| static void computeKnownBitsFromCond(const Value *V, Value *Cond, | |||
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Should we add a template helper to avoid duplicating the decomposition?
template<typename Callable>
void decomposeLogicalAndOr(Value *Cond, const Callable& Callback, unsigned Depth, bool Invert) {
Value *A, *B;
if (Depth < MaxAnalysisRecursionDepth &&
(Invert ? match(Cond, m_LogicalOr(m_Value(A), m_Value(B)))
: match(Cond, m_LogicalAnd(m_Value(A), m_Value(B))))) {
decomposeLogicalAndOr(A, Callback, Depth + 1, Invert);
decomposeLogicalAndOr(B, Callback, Depth + 1, Invert);
}
// TODO: match logical not
else
Callback(Cond, Invert);
}
template<typename Callable>
void decomposeLogicalAndOrWithWorkList(Value *Cond, const Callable& Callback) {
...
}
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We could do something like 07f0dde to allow reuse of the full logic for other ValueTracking helpers, e.g. #80941. Seems to add a little overhead, but not much: http://llvm-compile-time-tracker.com/compare.php?from=9ac82f0d3ecf6c13669b0c7940920460c037a292&to=07f0dde1783a0ce7ea17bcf29438989e9077b310&stat=instructions:u
This extends computeKnownBits() support for dominating conditions to also handle and/or conditions. We'll look through either and or or depending on which edge we're considering. This change is mainly for the sake of completeness, so we don't start missing optimizations if SimplifyCFG decides to merge some branches.
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This extends computeKnownBits() support for dominating conditions to also handle and/or conditions. We'll look through either and or or depending on which edge we're considering.
This change is mainly for the sake of completeness, so we don't start missing optimizations if SimplifyCFG decides to merge some branches.