RPCS3/llvm
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm.git synced 2025-04-09 17:41:10 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

Another BasicAA fix. If a value does not alias a GEP's base pointer, then it

Browse Source 
cannot alias the GEP. GEP pointer alias rule states this clearly:
A pointer value formed from a getelementptr instruction is associated with the
addresses associated with the first operand of the getelementptr.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84079 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2009-10-14 06:41:49 +00:00
parent df199f11c6
commit 681a33e26d
2 changed files with 76 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
lib/Analysis/BasicAliasAnalysis.cpp
View File

@ -428,8 +428,15 @@ BasicAliasAnalysis::aliasGEP(const Value *V1, unsigned V1Size,
SmallVector<Value*, 16> GEPOperands; SmallVector<Value*, 16> GEPOperands;
const Value *BasePtr = GetGEPOperands(V1, GEPOperands); const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
AliasResult R = aliasCheck(BasePtr, V1Size, V2, V2Size); AliasResult R = aliasCheck(BasePtr, ~0U, V2, V2Size);
if (R == MustAlias) { if (R != MustAlias)
// If V2 may alias GEP base pointer, conservatively returns MayAlias.
// If V2 is known not to alias GEP base pointer, then the two values
// cannot alias per GEP semantics: "A pointer value formed from a
// getelementptr instruction is associated with the addresses associated
// with the first operand of the getelementptr".
return R;
// If there is at least one non-zero constant index, we know they cannot // If there is at least one non-zero constant index, we know they cannot
// alias. // alias.
bool ConstantFound = false; bool ConstantFound = false;
@ -463,8 +470,7 @@ BasicAliasAnalysis::aliasGEP(const Value *V1, unsigned V1Size,
for (unsigned i = 0; i != GEPOperands.size(); ++i) for (unsigned i = 0; i != GEPOperands.size(); ++i)
if (!isa<ConstantInt>(GEPOperands[i])) if (!isa<ConstantInt>(GEPOperands[i]))
GEPOperands[i] = Constant::getNullValue(GEPOperands[i]->getType()); GEPOperands[i] = Constant::getNullValue(GEPOperands[i]->getType());
int64_t Offset = int64_t Offset = TD->getIndexedOffset(BasePtr->getType(),
TD->getIndexedOffset(BasePtr->getType(),
&GEPOperands[0], &GEPOperands[0],
GEPOperands.size()); GEPOperands.size());
@ -472,7 +478,6 @@ BasicAliasAnalysis::aliasGEP(const Value *V1, unsigned V1Size,
return NoAlias; return NoAlias;
} }
} }
}
return MayAlias; return MayAlias;
} }
@ -492,7 +497,9 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize,
Value *PV1 = PN->getIncomingValue(i); Value *PV1 = PN->getIncomingValue(i);
if (isa<PHINode>(PV1)) if (isa<PHINode>(PV1))
// If any of the source itself is a PHI, return MayAlias conservatively // If any of the source itself is a PHI, return MayAlias conservatively
// to avoid compile time explosion. // to avoid compile time explosion. The worst possible case is if both
// sides are PHI nodes. In which case, this is O(m x n) time where 'm'
// and 'n' are the number of PHI sources.
return MayAlias; return MayAlias;
if (UniqueSrc.insert(PV1)) if (UniqueSrc.insert(PV1))
V1Srcs.push_back(PV1); V1Srcs.push_back(PV1);

30
test/Analysis/BasicAA/2009-10-13-GEP-BaseNoAlias.ll Normal file
View File

@ -0,0 +1,30 @@
; RUN: opt < %s -aa-eval -print-all-alias-modref-info -disable-output |& grep {NoAlias:.*%P,.*@Z}
; If GEP base doesn't alias Z, then GEP doesn't alias Z.
; rdar://7282591
@Y = common global i32 0
@Z = common global i32 0
define void @foo(i32 %cond) nounwind ssp {
entry:
%a = alloca i32
%tmp = icmp ne i32 %cond, 0
br i1 %tmp, label %bb, label %bb1
bb:
%b = getelementptr i32* %a, i32 0
br label %bb2
bb1:
br label %bb2
bb2:
%P = phi i32* [ %b, %bb ], [ @Y, %bb1 ]
%tmp1 = load i32* @Z, align 4
store i32 123, i32* %P, align 4
%tmp2 = load i32* @Z, align 4
br label %return
return:
ret void
}