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Optimistically analyse Phi cycles

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Analyse Phis under the starting assumption that they are NoAlias. Recursively
look at their inputs.
If they MayAlias/MustAlias there must be an input that makes them so.

Addresses bug 14351.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169788 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Arnold Schwaighofer 2012-12-10 23:02:41 +00:00
parent 07f6a4fde0
commit 2b475922e6
2 changed files with 76 additions and 43 deletions
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54
lib/Analysis/BasicAliasAnalysis.cpp
View File

@ -1064,48 +1064,20 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
Location(V2, V2Size, V2TBAAInfo));
if (PN > V2)
std::swap(Locs.first, Locs.second);
// Find the first incoming phi value not from its parent.
unsigned f = 0;
while (PN->getIncomingBlock(f) == PN->getParent() &&
f < PN->getNumIncomingValues()-1)
++f;
AliasResult Alias =
aliasCheck(PN->getIncomingValue(f), PNSize, PNTBAAInfo,
PN2->getIncomingValueForBlock(PN->getIncomingBlock(f)),
V2Size, V2TBAAInfo);
if (Alias == MayAlias)
return MayAlias;
// If the first source of the PHI nodes NoAlias and the other inputs are
// the PHI node itself through some amount of recursion this does not add
// any new information so just return NoAlias.
// bb:
// ptr = ptr2 + 1
// loop:
// ptr_phi = phi [bb, ptr], [loop, ptr_plus_one]
// ptr2_phi = phi [bb, ptr2], [loop, ptr2_plus_one]
// ...
// ptr_plus_one = gep ptr_phi, 1
// ptr2_plus_one = gep ptr2_phi, 1
// We assume for the recursion that the the phis (ptr_phi, ptr2_phi) do
// not alias each other.
bool ArePhisAssumedNoAlias = false;
AliasResult OrigAliasResult = NoAlias;
if (Alias == NoAlias) {
// Pretend the phis do not alias.
assert(AliasCache.count(Locs) &&
"There must exist an entry for the phi node");
OrigAliasResult = AliasCache[Locs];
AliasCache[Locs] = NoAlias;
ArePhisAssumedNoAlias = true;
}
// Analyse the PHIs' inputs under the assumption that the PHIs are
// NoAlias.
// If the PHIs are May/MustAlias there must be (recursively) an input
// operand from outside the PHIs' cycle that is MayAlias/MustAlias or
// there must be an operation on the PHIs within the PHIs' value cycle
// that causes a MayAlias.
// Pretend the phis do not alias.
AliasResult Alias = NoAlias;
assert(AliasCache.count(Locs) &&
"There must exist an entry for the phi node");
AliasResult OrigAliasResult = AliasCache[Locs];
AliasCache[Locs] = NoAlias;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
if (i == f)
continue;
AliasResult ThisAlias =
aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
@ -1116,7 +1088,7 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
}
// Reset if speculation failed.
if (ArePhisAssumedNoAlias && Alias != NoAlias)
if (Alias != NoAlias)
AliasCache[Locs] = OrigAliasResult;
return Alias;

65
test/Analysis/BasicAA/phi-speculation.ll
View File

@ -4,9 +4,9 @@ target datalayout =
; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
; ptr_phi and ptr2_phi do not alias.
; CHECK: test_noalias_1
; CHECK: NoAlias: i32* %ptr2_phi, i32* %ptr_phi
define i32 @test_noalias(i32* %ptr2, i32 %count, i32* %coeff) {
define i32 @test_noalias_1(i32* %ptr2, i32 %count, i32* %coeff) {
entry:
%ptr = getelementptr inbounds i32* %ptr2, i64 1
br label %while.body
@ -31,3 +31,64 @@ while.body:
the_exit:
ret i32 %add
}
; CHECK: test_noalias_2
; CHECK: NoAlias: i32* %ptr_outer_phi, i32* %ptr_outer_phi2
; CHECK: NoAlias: i32* %ptr2_phi, i32* %ptr_phi
define i32 @test_noalias_2(i32* %ptr2, i32 %count, i32* %coeff) {
entry:
%ptr = getelementptr inbounds i32* %ptr2, i64 1
br label %outer.while.header
outer.while.header:
%ptr_outer_phi = phi i32* [%ptr_inc_outer, %outer.while.backedge], [ %ptr, %entry]
%ptr_outer_phi2 = phi i32* [%ptr2_inc_outer, %outer.while.backedge], [ %ptr2, %entry]
%num.outer = phi i32 [ %count, %entry ], [ %dec.outer, %outer.while.backedge ]
br label %while.body
while.body:
%num = phi i32 [ %count, %outer.while.header ], [ %dec, %while.body ]
%ptr_phi = phi i32* [ %ptr_outer_phi, %outer.while.header ], [ %ptr_inc, %while.body ]
%ptr2_phi = phi i32* [ %ptr_outer_phi2, %outer.while.header ], [ %ptr2_inc, %while.body ]
%result.09 = phi i32 [ 0 , %outer.while.header ], [ %add, %while.body ]
%dec = add nsw i32 %num, -1
%0 = load i32* %ptr_phi, align 4
store i32 %0, i32* %ptr2_phi, align 4
%1 = load i32* %coeff, align 4
%2 = load i32* %ptr_phi, align 4
%mul = mul nsw i32 %1, %2
%add = add nsw i32 %mul, %result.09
%tobool = icmp eq i32 %dec, 0
%ptr_inc = getelementptr inbounds i32* %ptr_phi, i64 1
%ptr2_inc = getelementptr inbounds i32* %ptr2_phi, i64 1
br i1 %tobool, label %outer.while.backedge, label %while.body
outer.while.backedge:
%ptr_inc_outer = getelementptr inbounds i32* %ptr_phi, i64 1
%ptr2_inc_outer = getelementptr inbounds i32* %ptr2_phi, i64 1
%dec.outer = add nsw i32 %num.outer, -1
%br.cond = icmp eq i32 %dec.outer, 0
br i1 %br.cond, label %the_exit, label %outer.while.header
the_exit:
ret i32 %add
}
; CHECK: test_noalias_3
; CHECK: MayAlias: i8* %ptr2_phi, i8* %ptr_phi
define i32 @test_noalias_3(i8* noalias %x, i8* noalias %y, i8* noalias %z,
i32 %count) {
entry:
br label %while.body
while.body:
%num = phi i32 [ %count, %entry ], [ %dec, %while.body ]
%ptr_phi = phi i8* [ %x, %entry ], [ %z, %while.body ]
%ptr2_phi = phi i8* [ %y, %entry ], [ %ptr_phi, %while.body ]
%dec = add nsw i32 %num, -1
%tobool = icmp eq i32 %dec, 0
br i1 %tobool, label %the_exit, label %while.body
the_exit:
ret i32 1
}