[llvm] r294897 - [ValueTracking] use nonnull argument attribute to eliminate null checks
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Sun Feb 12 07:35:35 PST 2017
Author: spatel
Date: Sun Feb 12 09:35:34 2017
New Revision: 294897
URL: http://llvm.org/viewvc/llvm-project?rev=294897&view=rev
Log:
[ValueTracking] use nonnull argument attribute to eliminate null checks
Enhancing value tracking's analysis of null-ness was suggested in D27855, so here's a first attempt at that.
This is part of solving:
https://llvm.org/bugs/show_bug.cgi?id=28430
Differential Revision: https://reviews.llvm.org/D28204
Modified:
llvm/trunk/include/llvm/Analysis/ValueTracking.h
llvm/trunk/lib/Analysis/ValueTracking.cpp
llvm/trunk/test/Analysis/ValueTracking/known-nonnull-at.ll
llvm/trunk/test/Transforms/InstCombine/call_nonnull_arg.ll
Modified: llvm/trunk/include/llvm/Analysis/ValueTracking.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ValueTracking.h?rev=294897&r1=294896&r2=294897&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/ValueTracking.h (original)
+++ llvm/trunk/include/llvm/Analysis/ValueTracking.h Sun Feb 12 09:35:34 2017
@@ -88,8 +88,10 @@ template <typename T> class ArrayRef;
/// Return true if the given value is known to be non-zero when defined. For
/// vectors, return true if every element is known to be non-zero when
- /// defined. Supports values with integer or pointer type and vectors of
- /// integers.
+ /// defined. For pointers, if the context instruction and dominator tree are
+ /// specified, perform context-sensitive analysis and return true if the
+ /// pointer couldn't possibly be null at the specified instruction.
+ /// Supports values with integer or pointer type and vectors of integers.
bool isKnownNonZero(const Value *V, const DataLayout &DL, unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=294897&r1=294896&r2=294897&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Sun Feb 12 09:35:34 2017
@@ -1824,10 +1824,12 @@ static bool rangeMetadataExcludesValue(c
return true;
}
-/// Return true if the given value is known to be non-zero when defined.
-/// For vectors return true if every element is known to be non-zero when
-/// defined. Supports values with integer or pointer type and vectors of
-/// integers.
+/// Return true if the given value is known to be non-zero when defined. For
+/// vectors, return true if every element is known to be non-zero when
+/// defined. For pointers, if the context instruction and dominator tree are
+/// specified, perform context-sensitive analysis and return true if the
+/// pointer couldn't possibly be null at the specified instruction.
+/// Supports values with integer or pointer type and vectors of integers.
bool isKnownNonZero(const Value *V, unsigned Depth, const Query &Q) {
if (auto *C = dyn_cast<Constant>(V)) {
if (C->isNullValue())
@@ -1870,7 +1872,7 @@ bool isKnownNonZero(const Value *V, unsi
// Check for pointer simplifications.
if (V->getType()->isPointerTy()) {
- if (isKnownNonNull(V))
+ if (isKnownNonNullAt(V, Q.CxtI, Q.DT))
return true;
if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V))
if (isGEPKnownNonNull(GEP, Depth, Q))
@@ -3473,6 +3475,16 @@ static bool isKnownNonNullFromDominating
if (NumUsesExplored >= DomConditionsMaxUses)
break;
NumUsesExplored++;
+
+ // If the value is used as an argument to a call or invoke, then argument
+ // attributes may provide an answer about null-ness.
+ if (auto CS = ImmutableCallSite(U))
+ if (auto *CalledFunc = CS.getCalledFunction())
+ for (const Argument &Arg : CalledFunc->args())
+ if (CS.getArgOperand(Arg.getArgNo()) == V &&
+ Arg.hasNonNullAttr() && DT->dominates(CS.getInstruction(), CtxI))
+ return true;
+
// Consider only compare instructions uniquely controlling a branch
CmpInst::Predicate Pred;
if (!match(const_cast<User *>(U),
Modified: llvm/trunk/test/Analysis/ValueTracking/known-nonnull-at.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ValueTracking/known-nonnull-at.ll?rev=294897&r1=294896&r2=294897&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ValueTracking/known-nonnull-at.ll (original)
+++ llvm/trunk/test/Analysis/ValueTracking/known-nonnull-at.ll Sun Feb 12 09:35:34 2017
@@ -8,8 +8,7 @@ declare void @bar(i8* %a, i8* nonnull %b
define i1 @caller1(i8* %x, i8* %y) {
; CHECK-LABEL: @caller1(
; CHECK-NEXT: call void @bar(i8* %x, i8* %y)
-; CHECK-NEXT: [[NULL_CHECK:%.*]] = icmp eq i8* %y, null
-; CHECK-NEXT: ret i1 [[NULL_CHECK]]
+; CHECK-NEXT: ret i1 false
;
call void @bar(i8* %x, i8* %y)
%null_check = icmp eq i8* %y, null
@@ -34,24 +33,68 @@ define i1 @caller2(i8* %x, i8* %y) {
define i1 @caller3(i8* %x, i8* %y) {
; CHECK-LABEL: @caller3(
; CHECK-NEXT: call void @bar(i8* %x, i8* %y)
-; CHECK-NEXT: [[NULL_CHECK:%.*]] = icmp ne i8* %y, null
-; CHECK-NEXT: ret i1 [[NULL_CHECK]]
+; CHECK-NEXT: ret i1 true
;
call void @bar(i8* %x, i8* %y)
%null_check = icmp ne i8* %y, null
ret i1 %null_check
}
-; Don't know anything about 'y'.
+; FIXME: The call is guaranteed to execute, so 'y' must be nonnull throughout.
define i1 @caller4(i8* %x, i8* %y) {
; CHECK-LABEL: @caller4(
-; CHECK-NEXT: call void @bar(i8* %y, i8* %x)
; CHECK-NEXT: [[NULL_CHECK:%.*]] = icmp ne i8* %y, null
+; CHECK-NEXT: call void @bar(i8* %x, i8* %y)
; CHECK-NEXT: ret i1 [[NULL_CHECK]]
;
- call void @bar(i8* %y, i8* %x)
%null_check = icmp ne i8* %y, null
+ call void @bar(i8* %x, i8* %y)
+ ret i1 %null_check
+}
+
+; The call to bar() does not dominate the null check, so no change.
+
+define i1 @caller5(i8* %x, i8* %y) {
+; CHECK-LABEL: @caller5(
+; CHECK-NEXT: [[NULL_CHECK:%.*]] = icmp eq i8* %y, null
+; CHECK-NEXT: br i1 [[NULL_CHECK]], label %t, label %f
+; CHECK: t:
+; CHECK-NEXT: ret i1 [[NULL_CHECK]]
+; CHECK: f:
+; CHECK-NEXT: call void @bar(i8* %x, i8* %y)
+; CHECK-NEXT: ret i1 [[NULL_CHECK]]
+;
+ %null_check = icmp eq i8* %y, null
+ br i1 %null_check, label %t, label %f
+t:
ret i1 %null_check
+f:
+ call void @bar(i8* %x, i8* %y)
+ ret i1 %null_check
+}
+
+; Make sure that an invoke works similarly to a call.
+
+declare i32 @esfp(...)
+
+define i1 @caller6(i8* %x, i8* %y) personality i8* bitcast (i32 (...)* @esfp to i8*){
+; CHECK-LABEL: @caller6(
+; CHECK-NEXT: invoke void @bar(i8* %x, i8* nonnull %y)
+; CHECK-NEXT: to label %cont unwind label %exc
+; CHECK: cont:
+; CHECK-NEXT: ret i1 false
+;
+ invoke void @bar(i8* %x, i8* nonnull %y)
+ to label %cont unwind label %exc
+
+cont:
+ %null_check = icmp eq i8* %y, null
+ ret i1 %null_check
+
+exc:
+ %lp = landingpad { i8*, i32 }
+ filter [0 x i8*] zeroinitializer
+ unreachable
}
Modified: llvm/trunk/test/Transforms/InstCombine/call_nonnull_arg.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/call_nonnull_arg.ll?rev=294897&r1=294896&r2=294897&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/call_nonnull_arg.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/call_nonnull_arg.ll Sun Feb 12 09:35:34 2017
@@ -31,7 +31,7 @@ dead:
unreachable
}
-; FIXME: The nonnull attribute in the 'bar' declaration could be
+; The nonnull attribute in the 'bar' declaration is
; propagated to the parameters of the 'baz' callsite.
declare void @bar(i8*, i8* nonnull)
@@ -40,7 +40,7 @@ declare void @baz(i8*, i8*)
define void @deduce_nonnull_from_another_call(i8* %a, i8* %b) {
; CHECK-LABEL: @deduce_nonnull_from_another_call(
; CHECK-NEXT: call void @bar(i8* %a, i8* %b)
-; CHECK-NEXT: call void @baz(i8* %b, i8* %b)
+; CHECK-NEXT: call void @baz(i8* nonnull %b, i8* nonnull %b)
; CHECK-NEXT: ret void
;
call void @bar(i8* %a, i8* %b)
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