mirror of
https://github.com/RPCSX/llvm.git
synced 2024-11-27 21:50:40 +00:00
92631b8db7
If a we have (a) a GEP and (b) a pointer based on an alloca, and the
beginning of the object the GEP points would have a negative offset with
repsect to the alloca, then the GEP can not alias pointer (b).
For example, consider code like:
struct { int f0, int f1, ...} foo;
...
foo alloca;
foo *random = bar(alloca);
int *f0 = &alloca.f0
int *f1 = &random->f1;
Which is lowered, approximately, to:
%alloca = alloca %struct.foo
%random = call %struct.foo* @random(%struct.foo* %alloca)
%f0 = getelementptr inbounds %struct, %struct.foo* %alloca, i32 0, i32 0
%f1 = getelementptr inbounds %struct, %struct.foo* %random, i32 0, i32 1
Assume %f1 and %f0 alias. Then %f1 would point into the object allocated
by %alloca. Since the %f1 GEP is inbounds, that means %random must also
point into the same object. But since %f0 points to the beginning of %alloca,
the highest %f1 can be is (%alloca + 3). This means %random can not be higher
than (%alloca - 1), and so is not inbounds, a contradiction.
Differential Revision: http://reviews.llvm.org/D20495
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270777 91177308-0d34-0410-b5e6-96231b3b80d8
|
||
|---|---|---|
| .. | ||
| AssumptionCache | ||
| BasicAA | ||
| BlockFrequencyInfo | ||
| BranchProbabilityInfo | ||
| CallGraph | ||
| CFLAliasAnalysis | ||
| CostModel | ||
| Delinearization | ||
| DemandedBits | ||
| DependenceAnalysis | ||
| DivergenceAnalysis | ||
| DominanceFrontier | ||
| Dominators | ||
| GlobalsModRef | ||
| LazyCallGraph | ||
| Lint | ||
| LoopAccessAnalysis | ||
| LoopInfo | ||
| MemoryDependenceAnalysis | ||
| PostDominators | ||
| RegionInfo | ||
| ScalarEvolution | ||
| ScopedNoAliasAA | ||
| TypeBasedAliasAnalysis | ||
| ValueTracking | ||
| alias-analysis-uses.ll | ||