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improve memdep to eliminate bitcasts (and aliases, and noop geps)

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early for the stated reasons: this allows it to find more 
equivalences and depend less on code layout.

llvm-svn: 82404
This commit is contained in:
Chris Lattner 2009-09-20 21:00:18 +00:00
parent b7d34131d1
commit a9a2b9a4cc
2 changed files with 40 additions and 1 deletions
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15
lib/Analysis/MemoryDependenceAnalysis.cpp
View File

@ -521,6 +521,13 @@ getNonLocalPointerDependency(Value *Pointer, bool isLoad, BasicBlock *FromBB,
const Type *EltTy = cast<PointerType>(Pointer->getType())->getElementType();
uint64_t PointeeSize = AA->getTypeStoreSize(EltTy);
// If Pointer is a bitcast instruction, chomp through to the pointee since
// they are must alias. This increases the effectiveness of caching by
// finding more equivalences, avoids having to phi translate the bitcast, and
// avoids conflicts where we are looking for two "different" values in the
// same block when they are really just must aliases.
Pointer = Pointer->stripPointerCasts();
// This is the set of blocks we've inspected, and the pointer we consider in
// each block. Because of critical edges, we currently bail out if querying
// a block with multiple different pointers. This can happen during PHI
@ -660,7 +667,6 @@ getNonLocalPointerDepFromBB(Value *Pointer, uint64_t PointeeSize,
SmallVectorImpl<NonLocalDepEntry> &Result,
DenseMap<BasicBlock*, Value*> &Visited,
bool SkipFirstBlock) {
// Look up the cached info for Pointer.
ValueIsLoadPair CacheKey(Pointer, isLoad);
@ -793,6 +799,13 @@ getNonLocalPointerDepFromBB(Value *Pointer, uint64_t PointeeSize,
BasicBlock *Pred = *PI;
Value *PredPtr = PtrPHI->getIncomingValueForBlock(Pred);
// If Pointer is a bitcast instruction, chomp through to the pointee since
// they are must alias. This increases the effectiveness of caching by
// finding more equivalences, avoids having to phi translate the bitcast, and
// avoids conflicts where we are looking for two "different" values in the
// same block when they are really just must aliases.
PredPtr = PredPtr->stripPointerCasts();
// Check to see if we have already visited this pred block with another
// pointer. If so, we can't do this lookup. This failure can occur
// with PHI translation when a critical edge exists and the PHI node in

26
test/Transforms/GVN/rle.ll
View File

@ -141,6 +141,32 @@ Cont:
; CHECK: ret i8 %A
}
;; non-local i32/float -> i8 load forwarding. This also tests that the "P3"
;; bitcast equivalence can be properly phi translated.
define i8 @coerce_mustalias_nonlocal1(i32* %P, i1 %cond) {
%P2 = bitcast i32* %P to float*
br i1 %cond, label %T, label %F
T:
store i32 42, i32* %P
br label %Cont
F:
store float 1.0, float* %P2
br label %Cont
Cont:
%P3 = bitcast i32* %P to i8*
%A = load i8* %P3
ret i8 %A
; CHECK: @coerce_mustalias_nonlocal1
; CHECK: Cont:
; CHECK: %A = phi i8 [
; CHECK-NOT: load
; CHECK: ret i8 %A
}
;; non-local i32 -> i8 partial redundancy load forwarding.
define i8 @coerce_mustalias_pre0(i32* %P, i1 %cond) {
%P3 = bitcast i32* %P to i8*