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improve validity check to handle constant-trip-count loops more

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aggressively.  In practice, this doesn't help anything though,
see the todo.

llvm-svn: 122660
This commit is contained in:
Chris Lattner 2011-01-01 19:54:22 +00:00
parent 4651f8b037
commit 9a9f43c4a2
2 changed files with 44 additions and 8 deletions
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24
lib/Transforms/Scalar/LoopIdiomRecognize.cpp
View File

@ -193,8 +193,7 @@ bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
return processLoopStoreOfSplatValue(SI, StoreSize, SplatValue, Ev, BECount);
// Handle the memcpy case here.
errs() << "Found strided store: " << *Ev << "\n";
// errs() << "Found strided store: " << *Ev << "\n";
return false;
}
@ -202,13 +201,23 @@ bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
/// mayLoopModRefLocation - Return true if the specified loop might do a load or
/// store to the same location that the specified store could store to, which is
/// a loop-strided access.
static bool mayLoopModRefLocation(StoreInst *SI, Loop *L, AliasAnalysis &AA) {
static bool mayLoopModRefLocation(StoreInst *SI, Loop *L, const SCEV *BECount,
unsigned StoreSize, AliasAnalysis &AA) {
// Get the location that may be stored across the loop. Since the access is
// strided positively through memory, we say that the modified location starts
// at the pointer and has infinite size.
// TODO: Could improve this for constant trip-count loops.
AliasAnalysis::Location StoreLoc =
AliasAnalysis::Location(SI->getPointerOperand());
uint64_t AccessSize = AliasAnalysis::UnknownSize;
// If the loop iterates a fixed number of times, we can refine the access size
// to be exactly the size of the memset, which is (BECount+1)*StoreSize
if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
AccessSize = (BECst->getValue()->getZExtValue()+1)*StoreSize;
// TODO: For this to be really effective, we have to dive into the pointer
// operand in the store. Store to &A[i] of 100 will always return may alias
// with store of &A[100], we need to StoreLoc to be "A" with size of 100,
// which will then no-alias a store to &A[100].
AliasAnalysis::Location StoreLoc(SI->getPointerOperand(), AccessSize);
for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
++BI)
@ -234,7 +243,8 @@ processLoopStoreOfSplatValue(StoreInst *SI, unsigned StoreSize,
// this into a memset in the loop preheader now if we want. However, this
// would be unsafe to do if there is anything else in the loop that may read
// or write to the aliased location. Check for an alias.
bool Unsafe=mayLoopModRefLocation(SI, CurLoop, getAnalysis<AliasAnalysis>());
bool Unsafe = mayLoopModRefLocation(SI, CurLoop, BECount, StoreSize,
getAnalysis<AliasAnalysis>());
SI->insertBefore(InstAfterStore);

28
test/Transforms/LoopIdiom/basic.ll
View File

@ -1,4 +1,4 @@
; RUN: opt -loop-idiom < %s -S | FileCheck %s
; RUN: opt -basicaa -loop-idiom < %s -S | FileCheck %s
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-apple-darwin10.0.0"
@ -65,3 +65,29 @@ for.end: ; preds = %entry
; CHECK-NOT: memset
; CHECK: ret void
}
;; TODO: We should be able to promote this memset. Not yet though.
define void @test4(i8* %Base) nounwind ssp {
bb.nph: ; preds = %entry
%Base100 = getelementptr i8* %Base, i64 1000
br label %for.body
for.body: ; preds = %bb.nph, %for.body
%indvar = phi i64 [ 0, %bb.nph ], [ %indvar.next, %for.body ]
%I.0.014 = getelementptr i8* %Base, i64 %indvar
store i8 0, i8* %I.0.014, align 1
;; Store beyond the range memset, should be safe to promote.
store i8 42, i8* %Base100
%indvar.next = add i64 %indvar, 1
%exitcond = icmp eq i64 %indvar.next, 100
br i1 %exitcond, label %for.end, label %for.body
for.end: ; preds = %for.body, %entry
ret void
; CHECK-TODO: @test4
; CHECK-TODO: call void @llvm.memset.p0i8.i64(i8* %Base, i8 0, i64 100, i32 1, i1 false)
; CHECK-TODO-NOT: store
}