Skip to content

Commit

Permalink
[ValueTracking] Handle icmp pred (trunc X), C in `computeKnownBitsF…
Browse files Browse the repository at this point in the history 
…romCmp` (#82803)

This patch handles the pattern `icmp pred (trunc X), C` in
`computeKnownBitsFromCmp` to infer low bits of `X` from dominating
conditions.
  • Loading branch information
@dtcxzyw
dtcxzyw authored Mar 6, 2024
1 parent 0cbbcf1 commit 3589cac
Show file tree
Hide file tree
Showing 2 changed files with 162 additions and 6 deletions.
28 changes: 22 additions & 6 deletions llvm/lib/Analysis/ValueTracking.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -708,6 +708,25 @@ static void computeKnownBitsFromCmp(const Value *V, CmpInst::Predicate Pred,
}
}

static void computeKnownBitsFromICmpCond(const Value *V, ICmpInst *Cmp,
KnownBits &Known,
const SimplifyQuery &SQ, bool Invert) {
ICmpInst::Predicate Pred =
Invert ? Cmp->getInversePredicate() : Cmp->getPredicate();
Value *LHS = Cmp->getOperand(0);
Value *RHS = Cmp->getOperand(1);

// Handle icmp pred (trunc V), C
if (match(LHS, m_Trunc(m_Specific(V)))) {
KnownBits DstKnown(LHS->getType()->getScalarSizeInBits());
computeKnownBitsFromCmp(LHS, Pred, LHS, RHS, DstKnown, SQ);
Known = Known.unionWith(DstKnown.anyext(Known.getBitWidth()));
return;
}

computeKnownBitsFromCmp(V, Pred, LHS, RHS, Known, SQ);
}

static void computeKnownBitsFromCond(const Value *V, Value *Cond,
KnownBits &Known, unsigned Depth,
const SimplifyQuery &SQ, bool Invert) {
Expand All @@ -727,9 +746,7 @@ static void computeKnownBitsFromCond(const Value *V, Value *Cond,
}

if (auto *Cmp = dyn_cast<ICmpInst>(Cond))
computeKnownBitsFromCmp(
V, Invert ? Cmp->getInversePredicate() : Cmp->getPredicate(),
Cmp->getOperand(0), Cmp->getOperand(1), Known, SQ);
computeKnownBitsFromICmpCond(V, Cmp, Known, SQ, Invert);
}

void llvm::computeKnownBitsFromContext(const Value *V, KnownBits &Known,
Expand Down Expand Up @@ -815,8 +832,7 @@ void llvm::computeKnownBitsFromContext(const Value *V, KnownBits &Known,
if (!isValidAssumeForContext(I, Q.CxtI, Q.DT))
continue;

computeKnownBitsFromCmp(V, Cmp->getPredicate(), Cmp->getOperand(0),
Cmp->getOperand(1), Known, Q);
computeKnownBitsFromICmpCond(V, Cmp, Known, Q, /*Invert=*/false);
}

// Conflicting assumption: Undefined behavior will occur on this execution
Expand Down Expand Up @@ -9133,7 +9149,7 @@ addValueAffectedByCondition(Value *V,

// Peek through unary operators to find the source of the condition.
Value *Op;
if (match(I, m_PtrToInt(m_Value(Op)))) {
if (match(I, m_CombineOr(m_PtrToInt(m_Value(Op)), m_Trunc(m_Value(Op))))) {
if (isa<Instruction>(Op) || isa<Argument>(Op))
InsertAffected(Op);
}
Expand Down
140 changes: 140 additions & 0 deletions llvm/test/Transforms/InstCombine/known-bits.ll
View file
Original file line number Diff line number Diff line change
Expand Up @@ -343,5 +343,145 @@ exit:
ret i8 %or2
}

define i32 @test_icmp_trunc1(i32 %x){
; CHECK-LABEL: @test_icmp_trunc1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[Y:%.*]] = trunc i32 [[X:%.*]] to i16
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i16 [[Y]], 7
; CHECK-NEXT: br i1 [[CMP]], label [[THEN:%.*]], label [[ELSE:%.*]]
; CHECK: then:
; CHECK-NEXT: ret i32 7
; CHECK: else:
; CHECK-NEXT: ret i32 0
;
entry:
%y = trunc i32 %x to i16
%cmp = icmp eq i16 %y, 7
br i1 %cmp, label %then, label %else
then:
%z = and i32 %x, 15
ret i32 %z
else:
ret i32 0
}

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
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i16 [[Y]], 7
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: ret i32 7
;
entry:
%y = trunc i32 %x to i16
%cmp = icmp eq i16 %y, 7
call void @llvm.assume(i1 %cmp)
%z = and i32 %x, 15
ret i32 %z
}

define i64 @test_icmp_trunc2(i64 %x) {
; CHECK-LABEL: @test_icmp_trunc2(
; CHECK-NEXT: [[CONV:%.*]] = trunc i64 [[X:%.*]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[CONV]], 12
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[SEXT:%.*]] = and i64 [[X]], 2147483647
; CHECK-NEXT: ret i64 [[SEXT]]
; CHECK: if.else:
; CHECK-NEXT: ret i64 0
;
%conv = trunc i64 %x to i32
%cmp = icmp sgt i32 %conv, 12
br i1 %cmp, label %if.then, label %if.else

if.then:
%sext = shl i64 %x, 32
%ret = ashr exact i64 %sext, 32
ret i64 %ret
if.else:
ret i64 0
}

define i64 @test_icmp_trunc3(i64 %n) {
; CHECK-LABEL: @test_icmp_trunc3(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CONV:%.*]] = trunc i64 [[N:%.*]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[CONV]], 96
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[RET:%.*]] = and i64 [[N]], 127
; CHECK-NEXT: ret i64 [[RET]]
; CHECK: if.else:
; CHECK-NEXT: ret i64 0
;
entry:
%conv = trunc i64 %n to i32
%cmp = icmp ult i32 %conv, 96
br i1 %cmp, label %if.then, label %if.else

if.then:
%ret = and i64 %n, 4294967295
ret i64 %ret

if.else:
ret i64 0
}

define i8 @test_icmp_trunc4(i64 %n) {
; CHECK-LABEL: @test_icmp_trunc4(
; CHECK-NEXT: [[CONV:%.*]] = trunc i64 [[N:%.*]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[CONV]], 10
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[CONV2:%.*]] = trunc i64 [[N]] to i8
; CHECK-NEXT: [[ADD:%.*]] = or disjoint i8 [[CONV2]], 48
; CHECK-NEXT: ret i8 [[ADD]]
; CHECK: if.else:
; CHECK-NEXT: ret i8 0
;
%conv = trunc i64 %n to i32
%cmp = icmp ult i32 %conv, 10
br i1 %cmp, label %if.then, label %if.else

if.then:
%conv2 = trunc i64 %n to i8
%add = add i8 %conv2, 48
ret i8 %add

if.else:
ret i8 0
}

define i64 @test_icmp_trunc5(i64 %n) {
; CHECK-LABEL: @test_icmp_trunc5(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SHR:%.*]] = ashr i64 [[N:%.*]], 47
; CHECK-NEXT: [[CONV1:%.*]] = trunc i64 [[SHR]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i32 [[CONV1]], -13
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[TMP0:%.*]] = and i64 [[SHR]], 15
; CHECK-NEXT: [[NOT:%.*]] = xor i64 [[TMP0]], 15
; CHECK-NEXT: ret i64 [[NOT]]
; CHECK: if.else:
; CHECK-NEXT: ret i64 13
;
entry:
%shr = ashr i64 %n, 47
%conv1 = trunc i64 %shr to i32
%cmp = icmp ugt i32 %conv1, -13
br i1 %cmp, label %if.then, label %if.else

if.then:
%and = and i64 %shr, 4294967295
%not = xor i64 %and, 4294967295
ret i64 %not

if.else:
ret i64 13
}

declare void @use(i1)
declare void @sink(i8)

0 comments on commit 3589cac

Please sign in to comment.