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[FunctionAttrs] try to extend nonnull-ness of arguments from a callsite back to its parent function
As discussed here: http://lists.llvm.org/pipermail/llvm-dev/2016-December/108182.html ...we should be able to propagate 'nonnull' info from a callsite back to its parent. The original motivation for this patch is our botched optimization of "dyn_cast" (PR28430), but this won't solve that problem. The transform is currently disabled by default while we wait for clang to work-around potential security problems: http://lists.llvm.org/pipermail/cfe-dev/2017-January/052066.html Differential Revision: https://reviews.llvm.org/D27855 llvm-svn: 294998
This commit is contained in:
Sanjay Patel
parent
f72eb8e1e7
commit
1e7c803052
@ -49,6 +49,14 @@ STATISTIC(NumNoAlias, "Number of function returns marked noalias");
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STATISTIC(NumNonNullReturn, "Number of function returns marked nonnull");
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STATISTIC(NumNoRecurse, "Number of functions marked as norecurse");
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// FIXME: This is disabled by default to avoid exposing security vulnerabilities
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// in C/C++ code compiled by clang:
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// http://lists.llvm.org/pipermail/cfe-dev/2017-January/052066.html
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static cl::opt<bool> EnableNonnullArgPropagation(
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"enable-nonnull-arg-prop", cl::Hidden,
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cl::desc("Try to propagate nonnull argument attributes from callsites to "
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"caller functions."));
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namespace {
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typedef SmallSetVector<Function *, 8> SCCNodeSet;
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}
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@ -531,6 +539,49 @@ static bool addArgumentReturnedAttrs(const SCCNodeSet &SCCNodes) {
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return Changed;
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}
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/// If a callsite has arguments that are also arguments to the parent function,
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/// try to propagate attributes from the callsite's arguments to the parent's
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/// arguments. This may be important because inlining can cause information loss
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/// when attribute knowledge disappears with the inlined call.
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static bool addArgumentAttrsFromCallsites(Function &F) {
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if (!EnableNonnullArgPropagation)
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return false;
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bool Changed = false;
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// For an argument attribute to transfer from a callsite to the parent, the
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// call must be guaranteed to execute every time the parent is called.
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// Conservatively, just check for calls in the entry block that are guaranteed
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// to execute.
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// TODO: This could be enhanced by testing if the callsite post-dominates the
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// entry block or by doing simple forward walks or backward walks to the
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// callsite.
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BasicBlock &Entry = F.getEntryBlock();
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for (Instruction &I : Entry) {
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if (auto CS = CallSite(&I)) {
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if (auto *CalledFunc = CS.getCalledFunction()) {
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for (auto &CSArg : CalledFunc->args()) {
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if (!CSArg.hasNonNullAttr())
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continue;
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// If the non-null callsite argument operand is an argument to 'F'
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// (the caller) and the call is guaranteed to execute, then the value
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// must be non-null throughout 'F'.
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auto *FArg = dyn_cast<Argument>(CS.getArgOperand(CSArg.getArgNo()));
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if (FArg && !FArg->hasNonNullAttr()) {
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FArg->addAttr(Attribute::NonNull);
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Changed = true;
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}
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}
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}
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}
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if (!isGuaranteedToTransferExecutionToSuccessor(&I))
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break;
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}
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return Changed;
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}
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/// Deduce nocapture attributes for the SCC.
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static bool addArgumentAttrs(const SCCNodeSet &SCCNodes) {
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bool Changed = false;
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@ -549,6 +600,8 @@ static bool addArgumentAttrs(const SCCNodeSet &SCCNodes) {
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if (!F->hasExactDefinition())
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continue;
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Changed |= addArgumentAttrsFromCallsites(*F);
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// Functions that are readonly (or readnone) and nounwind and don't return
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// a value can't capture arguments. Don't analyze them.
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if (F->onlyReadsMemory() && F->doesNotThrow() &&
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@ -1,4 +1,4 @@
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; RUN: opt -S -functionattrs %s | FileCheck %s
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; RUN: opt -S -functionattrs -enable-nonnull-arg-prop %s | FileCheck %s
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declare nonnull i8* @ret_nonnull()
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; Return a pointer trivially nonnull (call return attribute)
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@ -71,4 +71,148 @@ exit:
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ret i8* %phi
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}
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; Test propagation of nonnull callsite args back to caller.
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declare void @use1(i8* %x)
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declare void @use2(i8* %x, i8* %y);
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declare void @use3(i8* %x, i8* %y, i8* %z);
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declare void @use1nonnull(i8* nonnull %x);
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declare void @use2nonnull(i8* nonnull %x, i8* nonnull %y);
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declare void @use3nonnull(i8* nonnull %x, i8* nonnull %y, i8* nonnull %z);
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declare i8 @use1safecall(i8* %x) readonly nounwind ; readonly+nounwind guarantees that execution continues to successor
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; Can't extend non-null to parent for any argument because the 2nd call is not guaranteed to execute.
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define void @parent1(i8* %a, i8* %b, i8* %c) {
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; CHECK-LABEL: @parent1(i8* %a, i8* %b, i8* %c)
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; CHECK-NEXT: call void @use3(i8* %c, i8* %a, i8* %b)
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; CHECK-NEXT: call void @use3nonnull(i8* %b, i8* %c, i8* %a)
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; CHECK-NEXT: ret void
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;
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call void @use3(i8* %c, i8* %a, i8* %b)
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call void @use3nonnull(i8* %b, i8* %c, i8* %a)
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ret void
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}
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; Extend non-null to parent for all arguments.
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define void @parent2(i8* %a, i8* %b, i8* %c) {
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; CHECK-LABEL: @parent2(i8* nonnull %a, i8* nonnull %b, i8* nonnull %c)
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; CHECK-NEXT: call void @use3nonnull(i8* %b, i8* %c, i8* %a)
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; CHECK-NEXT: call void @use3(i8* %c, i8* %a, i8* %b)
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; CHECK-NEXT: ret void
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;
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call void @use3nonnull(i8* %b, i8* %c, i8* %a)
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call void @use3(i8* %c, i8* %a, i8* %b)
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ret void
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}
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; Extend non-null to parent for 1st argument.
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define void @parent3(i8* %a, i8* %b, i8* %c) {
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; CHECK-LABEL: @parent3(i8* nonnull %a, i8* %b, i8* %c)
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; CHECK-NEXT: call void @use1nonnull(i8* %a)
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; CHECK-NEXT: call void @use3(i8* %c, i8* %b, i8* %a)
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; CHECK-NEXT: ret void
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;
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call void @use1nonnull(i8* %a)
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call void @use3(i8* %c, i8* %b, i8* %a)
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ret void
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}
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; Extend non-null to parent for last 2 arguments.
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define void @parent4(i8* %a, i8* %b, i8* %c) {
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; CHECK-LABEL: @parent4(i8* %a, i8* nonnull %b, i8* nonnull %c)
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; CHECK-NEXT: call void @use2nonnull(i8* %c, i8* %b)
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; CHECK-NEXT: call void @use2(i8* %a, i8* %c)
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; CHECK-NEXT: call void @use1(i8* %b)
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; CHECK-NEXT: ret void
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;
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call void @use2nonnull(i8* %c, i8* %b)
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call void @use2(i8* %a, i8* %c)
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call void @use1(i8* %b)
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ret void
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}
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; The callsite must execute in order for the attribute to transfer to the parent.
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; It appears benign to extend non-null to the parent in this case, but we can't do that
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; because it would incorrectly propagate the wrong information to its callers.
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define void @parent5(i8* %a, i1 %a_is_notnull) {
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; CHECK-LABEL: @parent5(i8* %a, i1 %a_is_notnull)
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; CHECK-NEXT: br i1 %a_is_notnull, label %t, label %f
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; CHECK: t:
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; CHECK-NEXT: call void @use1nonnull(i8* %a)
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; CHECK-NEXT: ret void
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; CHECK: f:
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; CHECK-NEXT: ret void
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;
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br i1 %a_is_notnull, label %t, label %f
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t:
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call void @use1nonnull(i8* %a)
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ret void
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f:
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ret void
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}
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; The callsite must execute in order for the attribute to transfer to the parent.
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; The volatile load might trap, so there's no guarantee that we'll ever get to the call.
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define i8 @parent6(i8* %a, i8* %b) {
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; CHECK-LABEL: @parent6(i8* %a, i8* %b)
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; CHECK-NEXT: [[C:%.*]] = load volatile i8, i8* %b
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; CHECK-NEXT: call void @use1nonnull(i8* %a)
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; CHECK-NEXT: ret i8 [[C]]
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;
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%c = load volatile i8, i8* %b
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call void @use1nonnull(i8* %a)
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ret i8 %c
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}
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; The nonnull callsite is guaranteed to execute, so the argument must be nonnull throughout the parent.
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define i8 @parent7(i8* %a) {
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; CHECK-LABEL: @parent7(i8* nonnull %a)
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; CHECK-NEXT: [[RET:%.*]] = call i8 @use1safecall(i8* %a)
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; CHECK-NEXT: call void @use1nonnull(i8* %a)
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; CHECK-NEXT: ret i8 [[RET]]
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;
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%ret = call i8 @use1safecall(i8* %a)
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call void @use1nonnull(i8* %a)
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ret i8 %ret
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}
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; Make sure that an invoke works similarly to a call.
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declare i32 @esfp(...)
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define i1 @parent8(i8* %a, i8* %bogus1, i8* %b) personality i8* bitcast (i32 (...)* @esfp to i8*){
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; CHECK-LABEL: @parent8(i8* nonnull %a, i8* nocapture readnone %bogus1, i8* nonnull %b)
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; CHECK-NEXT: entry:
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; CHECK-NEXT: invoke void @use2nonnull(i8* %a, i8* %b)
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; CHECK-NEXT: to label %cont unwind label %exc
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; CHECK: cont:
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; CHECK-NEXT: [[NULL_CHECK:%.*]] = icmp eq i8* %b, null
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; CHECK-NEXT: ret i1 [[NULL_CHECK]]
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; CHECK: exc:
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; CHECK-NEXT: [[LP:%.*]] = landingpad { i8*, i32 }
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; CHECK-NEXT: filter [0 x i8*] zeroinitializer
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; CHECK-NEXT: unreachable
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;
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entry:
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invoke void @use2nonnull(i8* %a, i8* %b)
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to label %cont unwind label %exc
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cont:
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%null_check = icmp eq i8* %b, null
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ret i1 %null_check
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exc:
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%lp = landingpad { i8*, i32 }
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filter [0 x i8*] zeroinitializer
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unreachable
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}
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