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Fix a case where SROA did not correctly detect dead PHI or selects due

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to chains or cycles between PHIs and/or selects. Also add a couple of
really nice test cases reduced from Kostya's reports in PR13905 and
PR13906. Both are fixed by this patch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164596 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2012-09-25 10:03:40 +00:00
parent 00edf4c1d8
commit c303463dcc
2 changed files with 55 additions and 5 deletions
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15
lib/Transforms/Scalar/SROA.cpp
View File

@ -522,8 +522,10 @@ private:
void insertUse(Instruction &I, int64_t Offset, uint64_t Size, void insertUse(Instruction &I, int64_t Offset, uint64_t Size,
bool IsSplittable = false) { bool IsSplittable = false) {
// Completely skip uses which don't overlap the allocation. // Completely skip uses which have a zero size or don't overlap the
if ((Offset >= 0 && (uint64_t)Offset >= AllocSize) || // allocation.
if (Size == 0 ||
(Offset >= 0 && (uint64_t)Offset >= AllocSize) ||
(Offset < 0 && (uint64_t)-Offset >= Size)) { (Offset < 0 && (uint64_t)-Offset >= Size)) {
DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte use @" << Offset DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte use @" << Offset
<< " which starts past the end of the " << AllocSize << " which starts past the end of the " << AllocSize
@ -697,6 +699,9 @@ private:
SmallVector<std::pair<Instruction *, Instruction *>, 4> Uses; SmallVector<std::pair<Instruction *, Instruction *>, 4> Uses;
Visited.insert(Root); Visited.insert(Root);
Uses.push_back(std::make_pair(cast<Instruction>(*U), Root)); Uses.push_back(std::make_pair(cast<Instruction>(*U), Root));
// If there are no loads or stores, the access is dead. We mark that as
// a size zero access.
Size = 0;
do { do {
Instruction *I, *UsedI; Instruction *I, *UsedI;
llvm::tie(UsedI, I) = Uses.pop_back_val(); llvm::tie(UsedI, I) = Uses.pop_back_val();
@ -824,9 +829,9 @@ private:
} }
void insertUse(Instruction &User, int64_t Offset, uint64_t Size) { void insertUse(Instruction &User, int64_t Offset, uint64_t Size) {
// If the use extends outside of the allocation, record it as a dead use // If the use has a zero size or extends outside of the allocation, record
// for elimination later. // it as a dead use for elimination later.
if ((uint64_t)Offset >= AllocSize || if (Size == 0 || (uint64_t)Offset >= AllocSize ||
(Offset < 0 && (uint64_t)-Offset >= Size)) (Offset < 0 && (uint64_t)-Offset >= Size))
return markAsDead(User); return markAsDead(User);

45
test/Transforms/SROA/phi-and-select.ll
View File

@ -327,3 +327,48 @@ exit:
%load = load i32* %a %load = load i32* %a
ret i32 %load ret i32 %load
} }
define i32 @PR13905() {
; Check a pattern where we have a chain of dead phi nodes to ensure they are
; deleted and promotion can proceed.
; CHECK: @PR13905
; CHECK-NOT: alloca i32
; CHECK: ret i32 undef
entry:
%h = alloca i32
store i32 0, i32* %h
br i1 undef, label %loop1, label %exit
loop1:
%phi1 = phi i32* [ null, %entry ], [ %h, %loop1 ], [ %h, %loop2 ]
br i1 undef, label %loop1, label %loop2
loop2:
br i1 undef, label %loop1, label %exit
exit:
%phi2 = phi i32* [ %phi1, %loop2 ], [ null, %entry ]
ret i32 undef
}
define i32 @PR13906() {
; Another pattern which can lead to crashes due to failing to clear out dead
; PHI nodes or select nodes. This triggers subtly differently from the above
; cases because the PHI node is (recursively) alive, but the select is dead.
; CHECK: @PR13906
; CHECK-NOT: alloca
entry:
%c = alloca i32
store i32 0, i32* %c
br label %for.cond
for.cond:
%d.0 = phi i32* [ undef, %entry ], [ %c, %if.then ], [ %d.0, %for.cond ]
br i1 undef, label %if.then, label %for.cond
if.then:
%tmpcast.d.0 = select i1 undef, i32* %c, i32* %d.0
br label %for.cond
}