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[ValueTracking] Infer known bits fromfrom (icmp eq (and/or x,y), C) #87143

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[ValueTracking] Infer known bits fromfrom (icmp eq (and/or x,y), C) #87143

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fedce31
[ValueTracking] Add tests for computing known bits from `(icmp eq (an…
goldsteinn Mar 28, 2024
6a90629
[ValueTracking] Infer known bits fromfrom `(icmp eq (and/or x,y), C)`
goldsteinn Mar 28, 2024
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21 changes: 15 additions & 6 deletions llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -648,6 +648,7 @@ static void computeKnownBitsFromCmp(const Value *V, CmpInst::Predicate Pred,
auto m_V =
m_CombineOr(m_Specific(V), m_PtrToIntSameSize(Q.DL, m_Specific(V)));

Value *Y;
const APInt *Mask, *C;
uint64_t ShAmt;
switch (Pred) {
Expand All @@ -656,16 +657,18 @@ static void computeKnownBitsFromCmp(const Value *V, CmpInst::Predicate Pred,
if (match(LHS, m_V) && match(RHS, m_APInt(C))) {
Known = Known.unionWith(KnownBits::makeConstant(*C));
// assume(V & Mask = C)
} else if (match(LHS, m_And(m_V, m_APInt(Mask))) &&
} else if (match(LHS, m_c_And(m_V, m_Value(Y))) &&
match(RHS, m_APInt(C))) {
// For one bits in Mask, we can propagate bits from C to V.
Known.Zero |= ~*C & *Mask;
Known.One |= *C & *Mask;
Known.One |= *C;
if (match(Y, m_APInt(Mask)))
Known.Zero |= ~*C & *Mask;
// assume(V | Mask = C)
} else if (match(LHS, m_Or(m_V, m_APInt(Mask))) && match(RHS, m_APInt(C))) {
} else if (match(LHS, m_c_Or(m_V, m_Value(Y))) && match(RHS, m_APInt(C))) {
// For zero bits in Mask, we can propagate bits from C to V.
Known.Zero |= ~*C & ~*Mask;
Known.One |= *C & ~*Mask;
Known.Zero |= ~*C;
if (match(Y, m_APInt(Mask)))
Known.One |= *C & ~*Mask;
// assume(V ^ Mask = C)
} else if (match(LHS, m_Xor(m_V, m_APInt(Mask))) &&
match(RHS, m_APInt(C))) {
Expand Down Expand Up @@ -9276,11 +9279,17 @@ void llvm::findValuesAffectedByCondition(

if (ICmpInst::isEquality(Pred)) {
if (match(B, m_ConstantInt())) {
Value *Y;
// (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 if (match(A, m_And(m_Value(X), m_Value(Y))) ||
match(A, m_Or(m_Value(X), m_Value(Y)))) {
AddAffected(X);
AddAffected(Y);
}
}
} else {
// Handle (A + C1) u< C2, which is the canonical form of
Expand Down
106 changes: 101 additions & 5 deletions llvm/test/Transforms/InstCombine/known-bits.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -124,7 +124,6 @@ exit:
ret i8 %or2
}


define i8 @test_cond_and_bothways(i8 %x) {
; CHECK-LABEL: @test_cond_and_bothways(
; CHECK-NEXT: [[AND:%.*]] = and i8 [[X:%.*]], 91
Expand Down Expand Up @@ -181,8 +180,6 @@ exit:
ret i8 %or2
}



define i8 @test_cond_and_commuted(i8 %x, i1 %c1, i1 %c2) {
; CHECK-LABEL: @test_cond_and_commuted(
; CHECK-NEXT: [[AND:%.*]] = and i8 [[X:%.*]], 3
Expand Down Expand Up @@ -343,7 +340,7 @@ exit:
ret i8 %or2
}

define i32 @test_icmp_trunc1(i32 %x){
define i32 @test_icmp_trunc1(i32 %x) {
; CHECK-LABEL: @test_icmp_trunc1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[Y:%.*]] = trunc i32 [[X:%.*]] to i16
Expand All @@ -365,7 +362,7 @@ else:
ret i32 0
}

define i32 @test_icmp_trunc_assume(i32 %x){
define i32 @test_icmp_trunc_assume(i32 %x) {
; CHECK-LABEL: @test_icmp_trunc_assume(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[Y:%.*]] = trunc i32 [[X:%.*]] to i16
Expand Down Expand Up @@ -532,7 +529,106 @@ if.else:
ret i1 %other
}

define i8 @and_eq_bits_must_be_set(i8 %x, i8 %y) {
; CHECK-LABEL: @and_eq_bits_must_be_set(
; CHECK-NEXT: [[XY:%.*]] = and i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[XY]], 123
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: ret i8 1
;
%xy = and i8 %x, %y
%cmp = icmp eq i8 %xy, 123
call void @llvm.assume(i1 %cmp)
%r = and i8 %x, 1
ret i8 %r
}

define i8 @and_eq_bits_must_be_set2(i8 %x, i8 %y) {
; CHECK-LABEL: @and_eq_bits_must_be_set2(
; CHECK-NEXT: [[XY:%.*]] = and i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[XY]], 123
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: ret i8 11
;
%xy = and i8 %x, %y
%cmp = icmp eq i8 %xy, 123
call void @llvm.assume(i1 %cmp)
%r = and i8 %y, 11
ret i8 %r
}

define i8 @and_eq_bits_must_be_set2_partial_fail(i8 %x, i8 %y) {
; CHECK-LABEL: @and_eq_bits_must_be_set2_partial_fail(
; CHECK-NEXT: [[XY:%.*]] = and i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[XY]], 123
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[R:%.*]] = and i8 [[Y]], 111
; CHECK-NEXT: ret i8 [[R]]
;
%xy = and i8 %x, %y
%cmp = icmp eq i8 %xy, 123
call void @llvm.assume(i1 %cmp)
%r = and i8 %y, 111
ret i8 %r
}

define i8 @or_eq_bits_must_be_unset(i8 %x, i8 %y) {
; CHECK-LABEL: @or_eq_bits_must_be_unset(
; CHECK-NEXT: [[XY:%.*]] = or i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[XY]], 124
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: ret i8 0
;
%xy = or i8 %x, %y
%cmp = icmp eq i8 %xy, 124
call void @llvm.assume(i1 %cmp)
%r = and i8 %x, 3
ret i8 %r
}

define i8 @or_eq_bits_must_be_unset2(i8 %x, i8 %y) {
; CHECK-LABEL: @or_eq_bits_must_be_unset2(
; CHECK-NEXT: [[XY:%.*]] = or i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[XY]], 124
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: ret i8 0
;
%xy = or i8 %x, %y
%cmp = icmp eq i8 %xy, 124
call void @llvm.assume(i1 %cmp)
%r = and i8 %y, 1
ret i8 %r
}

define i8 @or_eq_bits_must_be_unset2_partial_fail(i8 %x, i8 %y) {
; CHECK-LABEL: @or_eq_bits_must_be_unset2_partial_fail(
; CHECK-NEXT: [[XY:%.*]] = or i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[XY]], 124
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[R:%.*]] = and i8 [[Y]], 4
; CHECK-NEXT: ret i8 [[R]]
;
%xy = or i8 %x, %y
%cmp = icmp eq i8 %xy, 124
call void @llvm.assume(i1 %cmp)
%r = and i8 %y, 7
ret i8 %r
}

define i8 @or_ne_bits_must_be_unset2_fail(i8 %x, i8 %y) {
; CHECK-LABEL: @or_ne_bits_must_be_unset2_fail(
; CHECK-NEXT: [[XY:%.*]] = or i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ne i8 [[XY]], 124
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[R:%.*]] = and i8 [[X]], 3
; CHECK-NEXT: ret i8 [[R]]
;
%xy = or i8 %x, %y
%cmp = icmp ne i8 %xy, 124
call void @llvm.assume(i1 %cmp)
%r = and i8 %x, 3
ret i8 %r
}

declare void @use(i1)
declare void @sink(i8)
10 changes: 5 additions & 5 deletions llvm/test/Transforms/InstCombine/zext-or-icmp.ll
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@@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -passes=instcombine -S | FileCheck %s
; RUN: opt < %s -passes='instcombine<no-verify-fixpoint>' -S | FileCheck %s
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We no longer reach fixed point because we end up unlocking a transform by creating a pattern we handle in knownbits.

If this is important, the fix here is to support sext/zext in the AssumptionCache.


define i8 @zext_or_icmp_icmp(i8 %a, i8 %b) {
; CHECK-LABEL: @zext_or_icmp_icmp(
Expand Down Expand Up @@ -180,11 +180,11 @@ define i8 @PR49475_infloop(i32 %t0, i16 %insert, i64 %e, i8 %i162) {
; CHECK-NEXT: [[SEXT:%.*]] = shl i64 [[SUB17]], 32
; CHECK-NEXT: [[CONV18:%.*]] = ashr exact i64 [[SEXT]], 32
; CHECK-NEXT: [[CMP:%.*]] = icmp sge i64 [[XOR]], [[CONV18]]
; CHECK-NEXT: [[CONV19:%.*]] = zext i1 [[CMP]] to i16
; CHECK-NEXT: [[OR21:%.*]] = or i16 [[CONV19]], [[INSERT]]
; CHECK-NEXT: [[TOBOOL23_NOT:%.*]] = icmp eq i16 [[OR21]], 0
; CHECK-NEXT: [[TRUNC44:%.*]] = zext i1 [[CMP]] to i8
; CHECK-NEXT: [[INC:%.*]] = add i8 [[TRUNC44]], [[I162]]
; CHECK-NEXT: [[TOBOOL23_NOT:%.*]] = xor i1 [[CMP]], true
; CHECK-NEXT: call void @llvm.assume(i1 [[TOBOOL23_NOT]])
; CHECK-NEXT: ret i8 [[I162]]
; CHECK-NEXT: ret i8 [[INC]]
;
%b = icmp eq i32 %t0, 0
%b2 = icmp eq i16 %insert, 0
Expand Down