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Enhance SRoA to be more aggressive about scalarization of aggregate allocas

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that have PHI or select uses of their element pointers.  This can often happen
when instcombine sinks two loads into a successor, inserting a phi or select.

With this patch, we can scalarize the alloca, but the pinned elements are not
yet promoted.  This is still a win for large aggregates where only one element
is used.  This fixes rdar://8904039 and part of rdar://7339113 (poor codegen
on stringswitch).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124070 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2011-01-23 08:27:54 +00:00
parent 491d8d4370
commit 145c532e68
2 changed files with 192 additions and 12 deletions
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126
lib/Transforms/Scalar/ScalarReplAggregates.cpp
View File

@ -82,6 +82,10 @@ namespace {
/// The alloca to promote.
AllocaInst *AI;
/// CheckedPHIs - This is a set of verified PHI nodes, to prevent infinite
/// looping and avoid redundant work.
SmallPtrSet<PHINode*, 8> CheckedPHIs;
/// isUnsafe - This is set to true if the alloca cannot be SROA'd.
bool isUnsafe : 1;
@ -116,10 +120,12 @@ namespace {
bool isSafeAllocaToScalarRepl(AllocaInst *AI);
void isSafeForScalarRepl(Instruction *I, uint64_t Offset, AllocaInfo &Info);
void isSafePHISelectUseForScalarRepl(Instruction *User, uint64_t Offset,
AllocaInfo &Info);
void isSafeGEP(GetElementPtrInst *GEPI, uint64_t &Offset, AllocaInfo &Info);
void isSafeMemAccess(uint64_t Offset, uint64_t MemSize,
const Type *MemOpType, bool isStore, AllocaInfo &Info,
Instruction *TheAccess);
Instruction *TheAccess, bool AllowWholeAccess);
bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size);
uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset,
const Type *&IdxTy);
@ -1086,13 +1092,14 @@ void SROA::isSafeForScalarRepl(Instruction *I, uint64_t Offset,
if (Length == 0)
return MarkUnsafe(Info, User);
isSafeMemAccess(Offset, Length->getZExtValue(), 0,
UI.getOperandNo() == 0, Info, MI);
UI.getOperandNo() == 0, Info, MI,
true /*AllowWholeAccess*/);
} else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
if (LI->isVolatile())
return MarkUnsafe(Info, User);
const Type *LIType = LI->getType();
isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType),
LIType, false, Info, LI);
LIType, false, Info, LI, true /*AllowWholeAccess*/);
Info.hasALoadOrStore = true;
} else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
@ -1102,8 +1109,65 @@ void SROA::isSafeForScalarRepl(Instruction *I, uint64_t Offset,
const Type *SIType = SI->getOperand(0)->getType();
isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType),
SIType, true, Info, SI);
SIType, true, Info, SI, true /*AllowWholeAccess*/);
Info.hasALoadOrStore = true;
} else if (isa<PHINode>(User) || isa<SelectInst>(User)) {
isSafePHISelectUseForScalarRepl(User, Offset, Info);
} else {
return MarkUnsafe(Info, User);
}
if (Info.isUnsafe) return;
}
}
/// isSafePHIUseForScalarRepl - If we see a PHI node or select using a pointer
/// derived from the alloca, we can often still split the alloca into elements.
/// This is useful if we have a large alloca where one element is phi'd
/// together somewhere: we can SRoA and promote all the other elements even if
/// we end up not being able to promote this one.
///
/// All we require is that the uses of the PHI do not index into other parts of
/// the alloca. The most important use case for this is single load and stores
/// that are PHI'd together, which can happen due to code sinking.
void SROA::isSafePHISelectUseForScalarRepl(Instruction *I, uint64_t Offset,
AllocaInfo &Info) {
// If we've already checked this PHI, don't do it again.
if (PHINode *PN = dyn_cast<PHINode>(I))
if (!Info.CheckedPHIs.insert(PN))
return;
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) {
isSafePHISelectUseForScalarRepl(BC, Offset, Info);
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
// Only allow "bitcast" GEPs for simplicity. We could generalize this,
// but would have to prove that we're staying inside of an element being
// promoted.
if (!GEPI->hasAllZeroIndices())
return MarkUnsafe(Info, User);
isSafePHISelectUseForScalarRepl(GEPI, Offset, Info);
} else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
if (LI->isVolatile())
return MarkUnsafe(Info, User);
const Type *LIType = LI->getType();
isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType),
LIType, false, Info, LI, false /*AllowWholeAccess*/);
Info.hasALoadOrStore = true;
} else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
// Store is ok if storing INTO the pointer, not storing the pointer
if (SI->isVolatile() || SI->getOperand(0) == I)
return MarkUnsafe(Info, User);
const Type *SIType = SI->getOperand(0)->getType();
isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType),
SIType, true, Info, SI, false /*AllowWholeAccess*/);
Info.hasALoadOrStore = true;
} else if (isa<PHINode>(User) || isa<SelectInst>(User)) {
isSafePHISelectUseForScalarRepl(User, Offset, Info);
} else {
return MarkUnsafe(Info, User);
}
@ -1187,11 +1251,15 @@ static bool isCompatibleAggregate(const Type *T1, const Type *T2) {
/// alloca or has an offset and size that corresponds to a component element
/// within it. The offset checked here may have been formed from a GEP with a
/// pointer bitcasted to a different type.
///
/// If AllowWholeAccess is true, then this allows uses of the entire alloca as a
/// unit. If false, it only allows accesses known to be in a single element.
void SROA::isSafeMemAccess(uint64_t Offset, uint64_t MemSize,
const Type *MemOpType, bool isStore,
AllocaInfo &Info, Instruction *TheAccess) {
AllocaInfo &Info, Instruction *TheAccess,
bool AllowWholeAccess) {
// Check if this is a load/store of the entire alloca.
if (Offset == 0 &&
if (Offset == 0 && AllowWholeAccess &&
MemSize == TD->getTypeAllocSize(Info.AI->getAllocatedType())) {
// This can be safe for MemIntrinsics (where MemOpType is 0) and integer
// loads/stores (which are essentially the same as the MemIntrinsics with
@ -1257,14 +1325,21 @@ bool SROA::TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size) {
/// instruction.
void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
SmallVector<AllocaInst*, 32> &NewElts) {
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E;) {
Use &TheUse = UI.getUse();
Instruction *User = cast<Instruction>(*UI++);
if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) {
RewriteBitCast(BC, AI, Offset, NewElts);
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
continue;
}
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
RewriteGEP(GEPI, AI, Offset, NewElts);
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
continue;
}
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
uint64_t MemSize = Length->getZExtValue();
if (Offset == 0 &&
@ -1272,7 +1347,10 @@ void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts);
// Otherwise the intrinsic can only touch a single element and the
// address operand will be updated, so nothing else needs to be done.
} else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
continue;
}
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
const Type *LIType = LI->getType();
if (isCompatibleAggregate(LIType, AI->getAllocatedType())) {
@ -1297,7 +1375,10 @@ void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
// If this is a load of the entire alloca to an integer, rewrite it.
RewriteLoadUserOfWholeAlloca(LI, AI, NewElts);
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
Value *Val = SI->getOperand(0);
const Type *SIType = Val->getType();
if (isCompatibleAggregate(SIType, AI->getAllocatedType())) {
@ -1320,6 +1401,26 @@ void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
// If this is a store of the entire alloca from an integer, rewrite it.
RewriteStoreUserOfWholeAlloca(SI, AI, NewElts);
}
continue;
}
if (isa<SelectInst>(User) || isa<PHINode>(User)) {
// If we have a PHI user of the alloca itself (as opposed to a GEP or
// bitcast) we have to rewrite it. GEP and bitcast uses will be RAUW'd to
// the new pointer.
if (!isa<AllocaInst>(I)) continue;
assert(Offset == 0 && NewElts[0] &&
"Direct alloca use should have a zero offset");
// If we have a use of the alloca, we know the derived uses will be
// utilizing just the first element of the scalarized result. Insert a
// bitcast of the first alloca before the user as required.
AllocaInst *NewAI = NewElts[0];
BitCastInst *BCI = new BitCastInst(NewAI, AI->getType(), "", NewAI);
NewAI->moveBefore(BCI);
TheUse = BCI;
continue;
}
}
}
@ -1859,6 +1960,7 @@ bool SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) {
return false;
}
}
return true;
}

78
test/Transforms/ScalarRepl/phi-select.ll Normal file
View File

@ -0,0 +1,78 @@
; RUN: opt %s -scalarrepl -S | FileCheck %s
; Test promotion of allocas that have phis and select users.
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-darwin10.2"
%struct.X = type { i32 }
%PairTy = type {i32, i32}
; CHECK: @test1
; CHECK: %a.0 = alloca i32
; CHECK: %b.0 = alloca i32
define i32 @test1(i32 %x) nounwind readnone ssp {
entry:
%a = alloca %struct.X, align 8 ; <%struct.X*> [#uses=2]
%b = alloca %struct.X, align 8 ; <%struct.X*> [#uses=2]
%0 = getelementptr inbounds %struct.X* %a, i64 0, i32 0 ; <i32*> [#uses=1]
store i32 1, i32* %0, align 8
%1 = getelementptr inbounds %struct.X* %b, i64 0, i32 0 ; <i32*> [#uses=1]
store i32 2, i32* %1, align 8
%2 = icmp eq i32 %x, 0 ; <i1> [#uses=1]
%p.0 = select i1 %2, %struct.X* %b, %struct.X* %a ; <%struct.X*> [#uses=1]
%3 = getelementptr inbounds %struct.X* %p.0, i64 0, i32 0 ; <i32*> [#uses=1]
%4 = load i32* %3, align 8 ; <i32> [#uses=1]
ret i32 %4
}
; CHECK: @test2
; CHECK: %A.0 = alloca i32
; CHECK: %A.1 = alloca i32
define i32 @test2(i1 %c) {
entry:
%A = alloca {i32, i32}
%B = getelementptr {i32, i32}* %A, i32 0, i32 0
store i32 1, i32* %B
br i1 %c, label %T, label %F
T:
%C = getelementptr {i32, i32}* %A, i32 0, i32 1
store i32 2, i32* %B
br label %F
F:
%X = phi i32* [%B, %entry], [%C, %T]
%Q = load i32* %X
ret i32 %Q
}
; CHECK: @test3
; CHECK: %A.0 = alloca i32
; CHECK: %A.1 = alloca i32
; rdar://8904039
define i32 @test3(i1 %c) {
entry:
%A = alloca {i32, i32}
%B = getelementptr {i32, i32}* %A, i32 0, i32 0
store i32 1, i32* %B
%C = getelementptr {i32, i32}* %A, i32 0, i32 1
store i32 2, i32* %B
%X = select i1 %c, i32* %B, i32* %C
%Q = load i32* %X
ret i32 %Q
}
;; We can't scalarize this, a use of the select is not an element access.
define i64 @test4(i1 %c) {
entry:
%A = alloca %PairTy
; CHECK: @test4
; CHECK: %A = alloca %PairTy
%B = getelementptr {i32, i32}* %A, i32 0, i32 0
store i32 1, i32* %B
%C = getelementptr {i32, i32}* %A, i32 0, i32 1
store i32 2, i32* %B
%X = select i1 %c, i32* %B, i32* %C
%Y = bitcast i32* %X to i64*
%Q = load i64* %Y
ret i64 %Q
}