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Make Value::isDereferenceablePointer() handle unreachable code blocks. (This 

returns false in the event the computation feeding into the pointer is
unreachable, which maybe ought to be true -- but this is at least consistent
with undef->isDereferenceablePointer().) Fixes PR11825!

llvm-svn: 148671
This commit is contained in:
Nick Lewycky 2012-01-23 00:05:17 +00:00
parent 0b7ad76bd0
commit c31ceda7d9
2 changed files with 45 additions and 7 deletions
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24
llvm/lib/VMCore/Value.cpp
View File

@ -349,7 +349,8 @@ Value *Value::stripPointerCasts() {
/// isDereferenceablePointer - Test if this value is always a pointer to
/// allocated and suitably aligned memory for a simple load or store.
bool Value::isDereferenceablePointer() const {
static bool isDereferenceablePointer(const Value *V,
SmallPtrSet<const Value *, 32> &Visited) {
// Note that it is not safe to speculate into a malloc'd region because
// malloc may return null.
// It's also not always safe to follow a bitcast, for example:
@ -358,20 +359,22 @@ bool Value::isDereferenceablePointer() const {
// be handled using TargetData to check sizes and alignments though.
// These are obviously ok.
if (isa<AllocaInst>(this)) return true;
if (isa<AllocaInst>(V)) return true;
// Global variables which can't collapse to null are ok.
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(this))
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
return !GV->hasExternalWeakLinkage();
// byval arguments are ok.
if (const Argument *A = dyn_cast<Argument>(this))
if (const Argument *A = dyn_cast<Argument>(V))
return A->hasByValAttr();
// For GEPs, determine if the indexing lands within the allocated object.
if (const GEPOperator *GEP = dyn_cast<GEPOperator>(this)) {
if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
// Conservatively require that the base pointer be fully dereferenceable.
if (!GEP->getOperand(0)->isDereferenceablePointer())
if (!Visited.insert(GEP->getOperand(0)))
return false;
if (!isDereferenceablePointer(GEP->getOperand(0), Visited))
return false;
// Check the indices.
gep_type_iterator GTI = gep_type_begin(GEP);
@ -405,6 +408,13 @@ bool Value::isDereferenceablePointer() const {
return false;
}
/// isDereferenceablePointer - Test if this value is always a pointer to
/// allocated and suitably aligned memory for a simple load or store.
bool Value::isDereferenceablePointer() const {
SmallPtrSet<const Value *, 32> Visited;
return ::isDereferenceablePointer(this, Visited);
}
/// DoPHITranslation - If this value is a PHI node with CurBB as its parent,
/// return the value in the PHI node corresponding to PredBB. If not, return
/// ourself. This is useful if you want to know the value something has in a

28
llvm/test/Transforms/SimplifyCFG/unreachable-blocks.ll Normal file
View File

@ -0,0 +1,28 @@
; RUN: opt -simplifycfg < %s -disable-output
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
target triple = "x86_64-pc-linux-gnu"
; PR11825
define void @test1() {
entry:
br label %return
while_block: ; preds = %and_if_cont2, %and_if_cont
%newlen = sub i32 %newlen, 1
%newptr = getelementptr i8* %newptr, i64 1
%test = icmp sgt i32 %newlen, 0
br i1 %test, label %and_if1, label %and_if_cont2
and_if1: ; preds = %while_block
%char = load i8* %newptr
%test2 = icmp ule i8 %char, 32
br label %and_if_cont2
and_if_cont2: ; preds = %and_if1, %while_block
%a18 = phi i1 [ %test, %while_block ], [ %test2, %and_if1 ]
br i1 %a18, label %while_block, label %return
return: ; preds = %and_if_cont2, %and_if_cont
ret void
}