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[ValueTracking] Allow context-sensitive nullness check for non-pointers 

Summary:
Same as D60846 and D69571 but with a fix for the problem encountered
after them. Both times it was a missing context adjustment in the
handling of PHI nodes.

The reproducers created from the bugs that caused the old commits to be
reverted are included.

Reviewers: nikic, nlopes, mkazantsev, spatel, dlrobertson, uabelho, hakzsam, hans

Subscribers: hiraditya, bollu, asbirlea, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71181
This commit is contained in:
Johannes Doerfert 2019-12-08 22:11:16 -06:00
parent 1164d43855
commit a7d992c0f2
6 changed files with 89 additions and 24 deletions
llvm
lib/Analysis
InstructionSimplify.cppValueTracking.cpp
test/Transforms
Attributor
nonnull.ll
InstCombine
known-non-zero.ll
InstSimplify
known-non-zero.ll
LICM
hoist-mustexec.ll

10
llvm/lib/Analysis/InstructionSimplify.cpp
View File

@ -543,10 +543,16 @@ static Value *ThreadCmpOverPHI(CmpInst::Predicate Pred, Value *LHS, Value *RHS,
// Evaluate the BinOp on the incoming phi values.
Value *CommonValue = nullptr;
for (Value *Incoming : PI->incoming_values()) {
for (unsigned u = 0, e = PI->getNumIncomingValues(); u < e; ++u) {
Value *Incoming = PI->getIncomingValue(u);
Instruction *InTI = PI->getIncomingBlock(u)->getTerminator();
// If the incoming value is the phi node itself, it can safely be skipped.
if (Incoming == PI) continue;
Value *V = SimplifyCmpInst(Pred, Incoming, RHS, Q, MaxRecurse);
// Change the context instruction to the "edge" that flows into the phi.
// This is important because that is where incoming is actually "evaluated"
// even though it is used later somewhere else.
Value *V = SimplifyCmpInst(Pred, Incoming, RHS, Q.getWithInstruction(InTI),
MaxRecurse);
// If the operation failed to simplify, or simplified to a different value
// to previously, then give up.
if (!V || (CommonValue && V != CommonValue))

36
llvm/lib/Analysis/ValueTracking.cpp
View File

@ -1353,6 +1353,8 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
for (unsigned i = 0; i != 2; ++i) {
Value *L = P->getIncomingValue(i);
Value *R = P->getIncomingValue(!i);
Instruction *RInst = P->getIncomingBlock(!i)->getTerminator();
Instruction *LInst = P->getIncomingBlock(i)->getTerminator();
Operator *LU = dyn_cast<Operator>(L);
if (!LU)
continue;
@ -1374,13 +1376,22 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
L = LL;
else
continue; // Check for recurrence with L and R flipped.
// 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).
Query RecQ = Q;
// Ok, we have a PHI of the form L op= R. Check for low
// zero bits.
computeKnownBits(R, Known2, Depth + 1, Q);
RecQ.CxtI = RInst;
computeKnownBits(R, Known2, Depth + 1, RecQ);
// We need to take the minimum number of known bits
KnownBits Known3(Known);
computeKnownBits(L, Known3, Depth + 1, Q);
RecQ.CxtI = LInst;
computeKnownBits(L, Known3, Depth + 1, RecQ);
Known.Zero.setLowBits(std::min(Known2.countMinTrailingZeros(),
Known3.countMinTrailingZeros()));
@ -1436,14 +1447,22 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
Known.Zero.setAllBits();
Known.One.setAllBits();
for (Value *IncValue : P->incoming_values()) {
for (unsigned u = 0, e = P->getNumIncomingValues(); u < e; ++u) {
Value *IncValue = P->getIncomingValue(u);
// Skip direct self references.
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).
Query RecQ = Q;
RecQ.CxtI = P->getIncomingBlock(u)->getTerminator();
Known2 = KnownBits(BitWidth);
// Recurse, but cap the recursion to one level, because we don't
// want to waste time spinning around in loops.
computeKnownBits(IncValue, Known2, MaxDepth - 1, Q);
computeKnownBits(IncValue, Known2, MaxDepth - 1, RecQ);
Known.Zero &= Known2.Zero;
Known.One &= Known2.One;
// If all bits have been ruled out, there's no need to check
@ -1902,8 +1921,8 @@ static bool isGEPKnownNonNull(const GEPOperator *GEP, unsigned Depth,
static bool isKnownNonNullFromDominatingCondition(const Value *V,
const Instruction *CtxI,
const DominatorTree *DT) {
assert(V->getType()->isPointerTy() && "V must be pointer type");
assert(!isa<ConstantData>(V) && "Did not expect ConstantPointerNull");
if (isa<Constant>(V))
return false;
if (!CtxI || !DT)
return false;
@ -2078,12 +2097,11 @@ bool isKnownNonZero(const Value *V, unsigned Depth, const Query &Q) {
}
}
if (isKnownNonNullFromDominatingCondition(V, Q.CxtI, Q.DT))
return true;
// Check for recursive pointer simplifications.
if (V->getType()->isPointerTy()) {
if (isKnownNonNullFromDominatingCondition(V, Q.CxtI, Q.DT))
return true;
// Look through bitcast operations, GEPs, and int2ptr instructions as they
// do not alter the value, or at least not the nullness property of the
// value, e.g., int2ptr is allowed to zero/sign extend the value.

2
llvm/test/Transforms/Attributor/nonnull.ll
View File

@ -789,7 +789,7 @@ define void @PR43833_simple(i32* %0, i32 %1) {
; ATTRIBUTOR_NPM-NEXT: ret void
; ATTRIBUTOR_NPM: 8:
; ATTRIBUTOR_NPM-NEXT: [[TMP9:%.*]] = phi i32 [ 1, [[TMP4]] ], [ [[TMP10:%.*]], [[TMP8]] ]
; ATTRIBUTOR_NPM-NEXT: tail call void @sink(i32* [[TMP6]])
; ATTRIBUTOR_NPM-NEXT: tail call void @sink(i32* nonnull [[TMP6]])
; ATTRIBUTOR_NPM-NEXT: [[TMP10]] = add nuw nsw i32 [[TMP9]], 1
; ATTRIBUTOR_NPM-NEXT: [[TMP11:%.*]] = icmp eq i32 [[TMP10]], [[TMP1]]
; ATTRIBUTOR_NPM-NEXT: br i1 [[TMP11]], label [[TMP7]], label [[TMP8]]

4
llvm/test/Transforms/InstCombine/known-non-zero.ll
View File

@ -13,7 +13,7 @@ define i32 @test0(i64 %x) {
; CHECK-NEXT: [[C:%.*]] = icmp eq i64 [[X:%.*]], 0
; CHECK-NEXT: br i1 [[C]], label [[EXIT:%.*]], label [[NON_ZERO:%.*]]
; CHECK: non_zero:
; CHECK-NEXT: [[CTZ:%.*]] = call i64 @llvm.cttz.i64(i64 [[X]], i1 false), !range !0
; CHECK-NEXT: [[CTZ:%.*]] = call i64 @llvm.cttz.i64(i64 [[X]], i1 true), !range !0
; CHECK-NEXT: [[CTZ32:%.*]] = trunc i64 [[CTZ]] to i32
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
@ -40,7 +40,7 @@ define i32 @test1(i64 %x) {
; CHECK-NEXT: [[C:%.*]] = icmp eq i64 [[X:%.*]], 0
; CHECK-NEXT: br i1 [[C]], label [[EXIT:%.*]], label [[NON_ZERO:%.*]]
; CHECK: non_zero:
; CHECK-NEXT: [[CTZ:%.*]] = call i64 @llvm.ctlz.i64(i64 [[X]], i1 false), !range !0
; CHECK-NEXT: [[CTZ:%.*]] = call i64 @llvm.ctlz.i64(i64 [[X]], i1 true), !range !0
; CHECK-NEXT: [[CTZ32:%.*]] = trunc i64 [[CTZ]] to i32
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:

57
llvm/test/Transforms/InstSimplify/known-non-zero.ll
View File

@ -7,8 +7,7 @@ define i64 @test0(i64 %x) {
; CHECK-NEXT: [[A:%.*]] = icmp eq i64 [[X:%.*]], 0
; CHECK-NEXT: br i1 [[A]], label [[EXIT:%.*]], label [[NON_ZERO:%.*]]
; CHECK: non_zero:
; CHECK-NEXT: [[B:%.*]] = icmp eq i64 [[X]], 0
; CHECK-NEXT: br i1 [[B]], label [[UNREACHABLE:%.*]], label [[EXIT]]
; CHECK-NEXT: br i1 false, label [[UNREACHABLE:%.*]], label [[EXIT]]
; CHECK: unreachable:
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
@ -37,8 +36,7 @@ define i64 @test1(i64 %x) {
; CHECK-NEXT: [[A:%.*]] = icmp eq i64 [[X:%.*]], 0
; CHECK-NEXT: br i1 [[A]], label [[EXIT:%.*]], label [[NON_ZERO:%.*]]
; CHECK: non_zero:
; CHECK-NEXT: [[B:%.*]] = icmp ugt i64 [[X]], 0
; CHECK-NEXT: br i1 [[B]], label [[EXIT]], label [[UNREACHABLE:%.*]]
; CHECK-NEXT: br i1 true, label [[EXIT]], label [[UNREACHABLE:%.*]]
; CHECK: unreachable:
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
@ -73,11 +71,9 @@ define i1 @test2(i64 %x, i1 %y) {
; CHECK: two:
; CHECK-NEXT: br label [[MAINBLOCK]]
; CHECK: mainblock:
; CHECK-NEXT: [[P:%.*]] = phi i64 [ [[X]], [[ONE]] ], [ 42, [[TWO]] ]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[P]], 0
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: [[RES:%.*]] = phi i1 [ [[CMP]], [[MAINBLOCK]] ], [ true, [[START:%.*]] ]
; CHECK-NEXT: [[RES:%.*]] = phi i1 [ false, [[MAINBLOCK]] ], [ true, [[START:%.*]] ]
; CHECK-NEXT: ret i1 [[RES]]
;
start:
@ -102,3 +98,50 @@ exit:
%res = phi i1 [ %cmp, %mainblock ], [ 1, %start ]
ret i1 %res
}
; The code below exposed a bug similar to the one exposed by D60846, see the commit 6ea477590085.
; In a nutshell, we should not replace %result.0 with 0 here.
define zeroext i8 @update_phi_query_loc_in_recursive_call(i8* nocapture readonly %p){
; CHECK-LABEL: @update_phi_query_loc_in_recursive_call(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[FOR_COND:%.*]]
; CHECK: for.cond:
; CHECK-NEXT: [[RESULT_0:%.*]] = phi i8 [ 0, [[ENTRY:%.*]] ], [ [[CONV2:%.*]], [[FOR_BODY:%.*]] ]
; CHECK-NEXT: [[SHIFT_0:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ 1, [[FOR_BODY]] ]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[SHIFT_0]], 0
; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_COND_CLEANUP:%.*]]
; CHECK: for.cond.cleanup:
; CHECK-NEXT: ret i8 [[RESULT_0]]
; CHECK: for.body:
; CHECK-NEXT: [[TMP0:%.*]] = load i8, i8* [[P:%.*]], align 1
; CHECK-NEXT: [[CONV:%.*]] = zext i8 [[TMP0]] to i32
; CHECK-NEXT: [[MUL:%.*]] = shl nuw nsw i32 [[SHIFT_0]], 3
; CHECK-NEXT: [[SHL:%.*]] = shl nuw nsw i32 [[CONV]], [[MUL]]
; CHECK-NEXT: [[TMP1:%.*]] = trunc i32 [[SHL]] to i8
; CHECK-NEXT: [[CONV2]] = or i8 [[RESULT_0]], [[TMP1]]
; CHECK-NEXT: br label [[FOR_COND]]
;
entry:
br label %for.cond
for.cond: ; preds = %for.body, %entry
%result.0 = phi i8 [ 0, %entry ], [ %conv2, %for.body ]
%shift.0 = phi i32 [ 0, %entry ], [ 1, %for.body ]
%cmp = icmp eq i32 %shift.0, 0
br i1 %cmp, label %for.body, label %for.cond.cleanup
for.cond.cleanup: ; preds = %for.cond
ret i8 %result.0
for.body: ; preds = %for.cond
%0 = load i8, i8* %p, align 1
%conv = zext i8 %0 to i32
%mul = shl nuw nsw i32 %shift.0, 3
%shl = shl nuw nsw i32 %conv, %mul
%1 = trunc i32 %shl to i8
%conv2 = or i8 %result.0, %1
%inc = add nuw nsw i32 %shift.0, 1
br label %for.cond
}

4
llvm/test/Transforms/LICM/hoist-mustexec.ll
View File

@ -129,8 +129,6 @@ fail:
}
; requires fact length is non-zero
; TODO: IsKnownNonNullFromDominatingConditions is currently only be done for
; pointers; should handle integers too
define i32 @test4(i32* noalias nocapture readonly %a) nounwind uwtable {
; CHECK-LABEL: @test4(
; CHECK-NEXT: entry:
@ -138,6 +136,7 @@ define i32 @test4(i32* noalias nocapture readonly %a) nounwind uwtable {
; CHECK-NEXT: [[IS_ZERO:%.*]] = icmp eq i32 [[LEN]], 0
; CHECK-NEXT: br i1 [[IS_ZERO]], label [[FAIL:%.*]], label [[PREHEADER:%.*]]
; CHECK: preheader:
; CHECK-NEXT: [[I1:%.*]] = load i32, i32* [[A]], align 4
; CHECK-NEXT: br label [[FOR_BODY:%.*]]
; CHECK: for.body:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 0, [[PREHEADER]] ], [ [[INC:%.*]], [[CONTINUE:%.*]] ]
@ -145,7 +144,6 @@ define i32 @test4(i32* noalias nocapture readonly %a) nounwind uwtable {
; CHECK-NEXT: [[R_CHK:%.*]] = icmp ult i32 [[IV]], [[LEN]]
; CHECK-NEXT: br i1 [[R_CHK]], label [[CONTINUE]], label [[FAIL_LOOPEXIT:%.*]]
; CHECK: continue:
; CHECK-NEXT: [[I1:%.*]] = load i32, i32* [[A]], align 4
; CHECK-NEXT: [[ADD]] = add nsw i32 [[I1]], [[ACC]]
; CHECK-NEXT: [[INC]] = add nuw nsw i32 [[IV]], 1
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp eq i32 [[INC]], 1000