[llvm] a56ba1f - [ValueTracking] Handle recursive select/PHI in ComputeKnownBits (#114689)
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Wed Jan 22 09:51:21 PST 2025
Author: goldsteinn
Date: 2025-01-22T11:51:18-06:00
New Revision: a56ba1fab07b2c9b1d0287bdf56cdad4d54a5f33
URL: https://github.com/llvm/llvm-project/commit/a56ba1fab07b2c9b1d0287bdf56cdad4d54a5f33
DIFF: https://github.com/llvm/llvm-project/commit/a56ba1fab07b2c9b1d0287bdf56cdad4d54a5f33.diff
LOG: [ValueTracking] Handle recursive select/PHI in ComputeKnownBits (#114689)
Finish porting #114008 to `KnownBits` (Follow up to #113707).
Added:
Modified:
llvm/lib/Analysis/ValueTracking.cpp
llvm/test/Analysis/ScalarEvolution/cycled_phis.ll
llvm/test/Analysis/ScalarEvolution/unknown_phis.ll
llvm/test/Transforms/InstCombine/known-phi-recurse.ll
llvm/test/Transforms/SimplifyCFG/switch-branch-fold-indirectbr-102351.ll
Removed:
################################################################################
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 6e2f0ebde9bb6c..38f88850be0f18 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -592,6 +592,36 @@ static bool cmpExcludesZero(CmpInst::Predicate Pred, const Value *RHS) {
return true;
}
+static void breakSelfRecursivePHI(const Use *U, const PHINode *PHI,
+ Value *&ValOut, Instruction *&CtxIOut) {
+ ValOut = U->get();
+ if (ValOut == PHI)
+ return;
+ CtxIOut = PHI->getIncomingBlock(*U)->getTerminator();
+ Value *V;
+ // If the Use is a select of this phi, compute analysis on other arm to break
+ // recursion.
+ // TODO: Min/Max
+ if (match(ValOut, m_Select(m_Value(), m_Specific(PHI), m_Value(V))) ||
+ match(ValOut, m_Select(m_Value(), m_Value(V), m_Specific(PHI))))
+ ValOut = V;
+
+ // Same for select, if this phi is 2-operand phi, compute analysis on other
+ // incoming value to break recursion.
+ // TODO: We could handle any number of incoming edges as long as we only have
+ // two unique values.
+ else if (auto *IncPhi = dyn_cast<PHINode>(ValOut);
+ IncPhi && IncPhi->getNumIncomingValues() == 2) {
+ for (int Idx = 0; Idx < 2; ++Idx) {
+ if (IncPhi->getIncomingValue(Idx) == PHI) {
+ ValOut = IncPhi->getIncomingValue(1 - Idx);
+ CtxIOut = IncPhi->getIncomingBlock(1 - Idx)->getTerminator();
+ break;
+ }
+ }
+ }
+}
+
static bool isKnownNonZeroFromAssume(const Value *V, const SimplifyQuery &Q) {
// Use of assumptions is context-sensitive. If we don't have a context, we
// cannot use them!
@@ -1641,25 +1671,19 @@ static void computeKnownBitsFromOperator(const Operator *I,
Known.Zero.setAllBits();
Known.One.setAllBits();
- for (unsigned u = 0, e = P->getNumIncomingValues(); u < e; ++u) {
- Value *IncValue = P->getIncomingValue(u);
+ for (const Use &U : P->operands()) {
+ Value *IncValue;
+ Instruction *CxtI;
+ breakSelfRecursivePHI(&U, P, IncValue, CxtI);
// Skip direct self references.
- if (IncValue == P) continue;
-
- // If the Use is a select of this phi, use the knownbit of the other
- // operand to break the recursion.
- if (auto *SI = dyn_cast<SelectInst>(IncValue)) {
- if (SI->getTrueValue() == P || SI->getFalseValue() == P)
- IncValue = SI->getTrueValue() == P ? SI->getFalseValue()
- : SI->getTrueValue();
- }
+ if (IncValue == P)
+ continue;
// Change the context instruction to the "edge" that flows into the
// phi. This is important because that is where the value is actually
// "evaluated" even though it is used later somewhere else. (see also
// D69571).
- SimplifyQuery RecQ = Q.getWithoutCondContext();
- RecQ.CxtI = P->getIncomingBlock(u)->getTerminator();
+ SimplifyQuery RecQ = Q.getWithoutCondContext().getWithInstruction(CxtI);
Known2 = KnownBits(BitWidth);
@@ -6053,30 +6077,13 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
bool First = true;
for (const Use &U : P->operands()) {
- Value *IncValue = U.get();
+ Value *IncValue;
+ Instruction *CxtI;
+ breakSelfRecursivePHI(&U, P, IncValue, CxtI);
// Skip direct self references.
if (IncValue == P)
continue;
- Instruction *CxtI = P->getIncomingBlock(U)->getTerminator();
-
- // If the Use is a select of this phi, use the fp class of the other
- // operand to break the recursion. Same around 2-operand phi nodes
- Value *V;
- if (match(IncValue, m_Select(m_Value(), m_Specific(P), m_Value(V))) ||
- match(IncValue, m_Select(m_Value(), m_Value(V), m_Specific(P)))) {
- IncValue = V;
- } else if (auto *IncPhi = dyn_cast<PHINode>(IncValue);
- IncPhi && IncPhi->getNumIncomingValues() == 2) {
- for (int Idx = 0; Idx < 2; ++Idx) {
- if (IncPhi->getIncomingValue(Idx) == P) {
- IncValue = IncPhi->getIncomingValue(1 - Idx);
- CxtI = IncPhi->getIncomingBlock(1 - Idx)->getTerminator();
- break;
- }
- }
- }
-
KnownFPClass KnownSrc;
// Recurse, but cap the recursion to two levels, because we don't want
// to waste time spinning around in loops. We need at least depth 2 to
diff --git a/llvm/test/Analysis/ScalarEvolution/cycled_phis.ll b/llvm/test/Analysis/ScalarEvolution/cycled_phis.ll
index ec244595e8fe39..478bcf94daf697 100644
--- a/llvm/test/Analysis/ScalarEvolution/cycled_phis.ll
+++ b/llvm/test/Analysis/ScalarEvolution/cycled_phis.ll
@@ -8,9 +8,9 @@ define void @test_01() {
; CHECK-LABEL: 'test_01'
; CHECK-NEXT: Classifying expressions for: @test_01
; CHECK-NEXT: %phi_1 = phi i32 [ 10, %entry ], [ %phi_2, %loop ]
-; CHECK-NEXT: --> %phi_1 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
+; CHECK-NEXT: --> %phi_1 U: [0,31) S: [0,31) Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
; CHECK-NEXT: %phi_2 = phi i32 [ 20, %entry ], [ %phi_1, %loop ]
-; CHECK-NEXT: --> %phi_2 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
+; CHECK-NEXT: --> %phi_2 U: [0,31) S: [0,31) Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
; CHECK-NEXT: %cond = call i1 @cond()
; CHECK-NEXT: --> %cond U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
; CHECK-NEXT: Determining loop execution counts for: @test_01
diff --git a/llvm/test/Analysis/ScalarEvolution/unknown_phis.ll b/llvm/test/Analysis/ScalarEvolution/unknown_phis.ll
index bdfe38f67de0b9..c6d430f96b7de1 100644
--- a/llvm/test/Analysis/ScalarEvolution/unknown_phis.ll
+++ b/llvm/test/Analysis/ScalarEvolution/unknown_phis.ll
@@ -39,9 +39,9 @@ define void @merge_values_with_ranges_looped(ptr %a_len_ptr, ptr %b_len_ptr) {
; CHECK-NEXT: %len_b = load i32, ptr %b_len_ptr, align 4, !range !0
; CHECK-NEXT: --> %len_b U: [0,2147483647) S: [0,2147483647)
; CHECK-NEXT: %p1 = phi i32 [ %len_a, %entry ], [ %p2, %loop ]
-; CHECK-NEXT: --> %p1 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
+; CHECK-NEXT: --> %p1 U: [0,-2147483648) S: [0,-2147483648) Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
; CHECK-NEXT: %p2 = phi i32 [ %len_b, %entry ], [ %p1, %loop ]
-; CHECK-NEXT: --> %p2 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
+; CHECK-NEXT: --> %p2 U: [0,-2147483648) S: [0,-2147483648) Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
; CHECK-NEXT: %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
; CHECK-NEXT: --> {0,+,1}<nuw><nsw><%loop> U: [0,100) S: [0,100) Exits: 99 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.next = add i32 %iv, 1
diff --git a/llvm/test/Transforms/InstCombine/known-phi-recurse.ll b/llvm/test/Transforms/InstCombine/known-phi-recurse.ll
index 9008ee9ca8e061..c05cca93b035c4 100644
--- a/llvm/test/Transforms/InstCombine/known-phi-recurse.ll
+++ b/llvm/test/Transforms/InstCombine/known-phi-recurse.ll
@@ -256,4 +256,142 @@ exit:
ret i8 %bool
}
+define i8 @knownbits_umax_select_test() {
+; CHECK-LABEL: @knownbits_umax_select_test(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[LOOP:%.*]]
+; CHECK: loop:
+; CHECK-NEXT: [[INDVAR:%.*]] = phi i8 [ 0, [[ENTRY:%.*]] ], [ [[CONTAIN:%.*]], [[LOOP]] ]
+; CHECK-NEXT: [[COND0:%.*]] = call i1 @cond()
+; CHECK-NEXT: [[CONTAIN]] = call i8 @llvm.umax.i8(i8 [[INDVAR]], i8 1)
+; CHECK-NEXT: [[COND1:%.*]] = call i1 @cond()
+; CHECK-NEXT: br i1 [[COND1]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK: exit:
+; CHECK-NEXT: [[BOOL:%.*]] = and i8 [[CONTAIN]], 1
+; CHECK-NEXT: ret i8 [[BOOL]]
+;
+entry:
+ br label %loop
+
+loop:
+ %indvar = phi i8 [ 0, %entry ], [ %contain, %loop ]
+ %cond0 = call i1 @cond()
+ %contain = call i8 @llvm.umax.i8(i8 1, i8 %indvar)
+ %cond1 = call i1 @cond()
+ br i1 %cond1, label %exit, label %loop
+
+exit:
+ %bool = and i8 %contain, 1
+ ret i8 %bool
+}
+
+define i8 @knownbits_phi_phi_test() {
+; CHECK-LABEL: @knownbits_phi_phi_test(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[LOOP:%.*]]
+; CHECK: loop:
+; CHECK-NEXT: [[INDVAR:%.*]] = phi i8 [ 0, [[ENTRY:%.*]] ], [ [[CONTAIN:%.*]], [[LOOP_BB1:%.*]] ]
+; CHECK-NEXT: [[COND0:%.*]] = call i1 @cond()
+; CHECK-NEXT: br i1 [[COND0]], label [[LOOP_BB0:%.*]], label [[LOOP_BB1]]
+; CHECK: loop.bb0:
+; CHECK-NEXT: call void @side.effect()
+; CHECK-NEXT: br label [[LOOP_BB1]]
+; CHECK: loop.bb1:
+; CHECK-NEXT: [[CONTAIN]] = phi i8 [ 1, [[LOOP_BB0]] ], [ [[INDVAR]], [[LOOP]] ]
+; CHECK-NEXT: [[COND1:%.*]] = call i1 @cond()
+; CHECK-NEXT: br i1 [[COND1]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK: exit:
+; CHECK-NEXT: ret i8 [[CONTAIN]]
+;
+entry:
+ br label %loop
+
+loop:
+ %indvar = phi i8 [ 0, %entry ], [ %contain, %loop.bb1 ]
+ %cond0 = call i1 @cond()
+ br i1 %cond0, label %loop.bb0, label %loop.bb1
+loop.bb0:
+ call void @side.effect()
+ br label %loop.bb1
+loop.bb1:
+ %contain = phi i8 [ 1, %loop.bb0 ], [ %indvar, %loop ]
+ %cond1 = call i1 @cond()
+ br i1 %cond1, label %exit, label %loop
+
+exit:
+ %bool = and i8 %contain, 1
+ ret i8 %bool
+}
+
+
+define i1 @known_non_zero_phi_phi_test() {
+; CHECK-LABEL: @known_non_zero_phi_phi_test(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[LOOP:%.*]]
+; CHECK: loop:
+; CHECK-NEXT: [[INDVAR:%.*]] = phi i8 [ 2, [[ENTRY:%.*]] ], [ [[CONTAIN:%.*]], [[LOOP_BB1:%.*]] ]
+; CHECK-NEXT: [[COND0:%.*]] = call i1 @cond()
+; CHECK-NEXT: br i1 [[COND0]], label [[LOOP_BB0:%.*]], label [[LOOP_BB1]]
+; CHECK: loop.bb0:
+; CHECK-NEXT: call void @side.effect()
+; CHECK-NEXT: br label [[LOOP_BB1]]
+; CHECK: loop.bb1:
+; CHECK-NEXT: [[CONTAIN]] = phi i8 [ 1, [[LOOP_BB0]] ], [ [[INDVAR]], [[LOOP]] ]
+; CHECK-NEXT: [[COND1:%.*]] = call i1 @cond()
+; CHECK-NEXT: br i1 [[COND1]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK: exit:
+; CHECK-NEXT: [[BOOL:%.*]] = icmp eq i8 [[CONTAIN]], 0
+; CHECK-NEXT: ret i1 [[BOOL]]
+;
+entry:
+ br label %loop
+
+loop:
+ %indvar = phi i8 [ 2, %entry ], [ %contain, %loop.bb1 ]
+ %cond0 = call i1 @cond()
+ br i1 %cond0, label %loop.bb0, label %loop.bb1
+loop.bb0:
+ call void @side.effect()
+ br label %loop.bb1
+loop.bb1:
+ %contain = phi i8 [ 1, %loop.bb0 ], [ %indvar, %loop ]
+ %cond1 = call i1 @cond()
+ br i1 %cond1, label %exit, label %loop
+
+exit:
+ %bool = icmp eq i8 %contain, 0
+ ret i1 %bool
+}
+
+define i1 @known_non_zero_phi_select_test() {
+; CHECK-LABEL: @known_non_zero_phi_select_test(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[LOOP:%.*]]
+; CHECK: loop:
+; CHECK-NEXT: [[INDVAR:%.*]] = phi i8 [ 2, [[ENTRY:%.*]] ], [ [[CONTAIN:%.*]], [[LOOP]] ]
+; CHECK-NEXT: [[COND0:%.*]] = call i1 @cond()
+; CHECK-NEXT: [[CONTAIN]] = select i1 [[COND0]], i8 1, i8 [[INDVAR]]
+; CHECK-NEXT: [[COND1:%.*]] = call i1 @cond()
+; CHECK-NEXT: br i1 [[COND1]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK: exit:
+; CHECK-NEXT: [[BOOL:%.*]] = icmp eq i8 [[CONTAIN]], 0
+; CHECK-NEXT: ret i1 [[BOOL]]
+;
+entry:
+ br label %loop
+
+loop:
+ %indvar = phi i8 [ 2, %entry ], [ %contain, %loop ]
+ %cond0 = call i1 @cond()
+ %contain = select i1 %cond0, i8 1, i8 %indvar
+ %cond1 = call i1 @cond()
+ br i1 %cond1, label %exit, label %loop
+
+exit:
+ %bool = icmp eq i8 %contain, 0
+ ret i1 %bool
+}
+
declare i1 @cond()
+declare void @side.effect()
+
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-branch-fold-indirectbr-102351.ll b/llvm/test/Transforms/SimplifyCFG/switch-branch-fold-indirectbr-102351.ll
index d3713be8358db4..0308d513240fef 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch-branch-fold-indirectbr-102351.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch-branch-fold-indirectbr-102351.ll
@@ -6,35 +6,29 @@ define i32 @foo.1(i32 %arg, ptr %arg1) {
; CHECK-SAME: i32 [[ARG:%.*]], ptr [[ARG1:%.*]]) {
; CHECK-NEXT: [[BB:.*]]:
; CHECK-NEXT: [[ALLOCA:%.*]] = alloca [2 x ptr], align 16
-; CHECK-NEXT: store ptr blockaddress(@foo.1, %[[BB8:.*]]), ptr [[ALLOCA]], align 16
+; CHECK-NEXT: store ptr blockaddress(@foo.1, %[[BB2:.*]]), ptr [[ALLOCA]], align 16
; CHECK-NEXT: [[GETELEMENTPTR:%.*]] = getelementptr inbounds [2 x ptr], ptr [[ALLOCA]], i64 0, i64 1
; CHECK-NEXT: store ptr blockaddress(@foo.1, %[[BB16:.*]]), ptr [[GETELEMENTPTR]], align 8
-; CHECK-NEXT: br label %[[PREFBB2:.*]]
-; CHECK: [[PREFBB2]]:
-; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ 0, %[[BB]] ], [ [[PHI14:%.*]], %[[BB13:.*]] ]
-; CHECK-NEXT: [[PHI3:%.*]] = phi i32 [ 0, %[[BB]] ], [ [[PHI15:%.*]], %[[BB13]] ]
-; CHECK-NEXT: switch i32 [[PHI]], label %[[BB13]] [
-; CHECK-NEXT: i32 0, label %[[PREFBB18:.*]]
-; CHECK-NEXT: i32 1, label %[[BB8]]
+; CHECK-NEXT: br label %[[BB2]]
+; CHECK: [[BB2]]:
+; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ 0, %[[BB]] ], [ 2, %[[BB18:.*]] ]
+; CHECK-NEXT: [[PHI3:%.*]] = phi i32 [ 0, %[[BB]] ], [ [[ARG]], %[[BB18]] ]
+; CHECK-NEXT: switch i32 [[PHI]], label %[[BB2_UNREACHABLEDEFAULT:.*]] [
+; CHECK-NEXT: i32 0, label %[[BB18]]
; CHECK-NEXT: i32 2, label %[[PREFBB11:.*]]
; CHECK-NEXT: ]
-; CHECK: [[BB8]]:
-; CHECK-NEXT: [[PHI10:%.*]] = phi i32 [ [[ARG]], %[[PREFBB18]] ], [ [[PHI3]], %[[PREFBB2]] ]
-; CHECK-NEXT: br label %[[BB13]]
; CHECK: [[PREFBB11]]:
; CHECK-NEXT: [[CALL:%.*]] = call i32 @wombat(i32 noundef [[PHI3]])
; CHECK-NEXT: [[ADD:%.*]] = add nsw i32 [[PHI3]], 1
-; CHECK-NEXT: br label %[[PREFBB18]]
-; CHECK: [[BB13]]:
-; CHECK-NEXT: [[PHI14]] = phi i32 [ [[PHI]], %[[PREFBB2]] ], [ 2, %[[BB8]] ]
-; CHECK-NEXT: [[PHI15]] = phi i32 [ [[PHI3]], %[[PREFBB2]] ], [ [[PHI10]], %[[BB8]] ]
-; CHECK-NEXT: br label %[[PREFBB2]]
+; CHECK-NEXT: br label %[[BB18]]
+; CHECK: [[BB2_UNREACHABLEDEFAULT]]:
+; CHECK-NEXT: unreachable
; CHECK: [[BB16]]:
; CHECK-NEXT: [[CALL17:%.*]] = call i32 @wombat(i32 noundef [[ARG]])
; CHECK-NEXT: ret i32 0
-; CHECK: [[PREFBB18]]:
+; CHECK: [[BB18]]:
; CHECK-NEXT: [[LOAD:%.*]] = load ptr, ptr [[ARG1]], align 8
-; CHECK-NEXT: indirectbr ptr [[LOAD]], [label %[[BB8]], label %bb16]
+; CHECK-NEXT: indirectbr ptr [[LOAD]], [label %[[BB2]], label %bb16]
;
bb:
%alloca = alloca [2 x ptr], align 16
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