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Make SimplifyDemandedVectorElts simplify vectors with multiple 

users, and teach it about shufflevector instructions.

Also, fix a subtle bug in SimplifyDemandedVectorElts'
insertelement code.

This is a patch that was originally written by Eli Friedman,
with some fixes and cleanup by me.

llvm-svn: 55995
This commit is contained in:
Dan Gohman 2008-09-09 18:11:14 +00:00
parent 4f1c7c3773
commit 86fb5b48de
2 changed files with 115 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

116
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -1355,8 +1355,7 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, uint64_t DemandedElts,
unsigned VWidth = cast<VectorType>(V->getType())->getNumElements();
assert(VWidth <= 64 && "Vector too wide to analyze!");
uint64_t EltMask = ~0ULL >> (64-VWidth);
assert(DemandedElts != EltMask && (DemandedElts & ~EltMask) == 0 &&
"Invalid DemandedElts!");
assert((DemandedElts & ~EltMask) == 0 && "Invalid DemandedElts!");
if (isa<UndefValue>(V)) {
// If the entire vector is undefined, just return this info.
@ -1400,14 +1399,23 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, uint64_t DemandedElts,
return ConstantVector::get(Elts);
}
if (!V->hasOneUse()) { // Other users may use these bits.
if (Depth != 0) { // Not at the root.
// Limit search depth.
if (Depth == 10)
return false;
// If multiple users are using the root value, procede with
// simplification conservatively assuming that all elements
// are needed.
if (!V->hasOneUse()) {
// Quit if we find multiple users of a non-root value though.
// They'll be handled when it's their turn to be visited by
// the main instcombine process.
if (Depth != 0)
// TODO: Just compute the UndefElts information recursively.
return false;
}
return false;
} else if (Depth == 10) { // Limit search depth.
return false;
// Conservatively assume that all elements are needed.
DemandedElts = EltMask;
}
Instruction *I = dyn_cast<Instruction>(V);
@ -1446,7 +1454,65 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, uint64_t DemandedElts,
if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; }
// The inserted element is defined.
UndefElts |= 1ULL << IdxNo;
UndefElts &= ~(1ULL << IdxNo);
break;
}
case Instruction::ShuffleVector: {
ShuffleVectorInst *Shuffle = cast<ShuffleVectorInst>(I);
uint64_t LeftDemanded = 0, RightDemanded = 0;
for (unsigned i = 0; i < VWidth; i++) {
if (DemandedElts & (1ULL << i)) {
unsigned MaskVal = Shuffle->getMaskValue(i);
if (MaskVal != -1u) {
assert(MaskVal < VWidth * 2 &&
"shufflevector mask index out of range!");
if (MaskVal < VWidth)
LeftDemanded |= 1ULL << MaskVal;
else
RightDemanded |= 1ULL << (MaskVal - VWidth);
}
}
}
TmpV = SimplifyDemandedVectorElts(I->getOperand(0), LeftDemanded,
UndefElts2, Depth+1);
if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; }
uint64_t UndefElts3;
TmpV = SimplifyDemandedVectorElts(I->getOperand(1), RightDemanded,
UndefElts3, Depth+1);
if (TmpV) { I->setOperand(1, TmpV); MadeChange = true; }
bool NewUndefElts = false;
for (unsigned i = 0; i < VWidth; i++) {
unsigned MaskVal = Shuffle->getMaskValue(i);
if (MaskVal == -1) {
uint64_t NewBit = 1ULL << i;
UndefElts |= NewBit;
} else if (MaskVal < VWidth) {
uint64_t NewBit = ((UndefElts2 >> MaskVal) & 1) << i;
NewUndefElts |= NewBit;
UndefElts |= NewBit;
} else {
uint64_t NewBit = ((UndefElts3 >> (MaskVal - VWidth)) & 1) << i;
NewUndefElts |= NewBit;
UndefElts |= NewBit;
}
}
if (NewUndefElts) {
// Add additional discovered undefs.
std::vector<Constant*> Elts;
for (unsigned i = 0; i < VWidth; ++i) {
if (UndefElts & (1ULL << i))
Elts.push_back(UndefValue::get(Type::Int32Ty));
else
Elts.push_back(ConstantInt::get(Type::Int32Ty,
Shuffle->getMaskValue(i)));
}
I->setOperand(2, ConstantVector::get(Elts));
MadeChange = true;
}
break;
}
case Instruction::BitCast: {
@ -11224,31 +11290,13 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
// Undefined shuffle mask -> undefined value.
if (isa<UndefValue>(SVI.getOperand(2)))
return ReplaceInstUsesWith(SVI, UndefValue::get(SVI.getType()));
// If we have shuffle(x, undef, mask) and any elements of mask refer to
// the undef, change them to undefs.
if (isa<UndefValue>(SVI.getOperand(1))) {
// Scan to see if there are any references to the RHS. If so, replace them
// with undef element refs and set MadeChange to true.
for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
if (Mask[i] >= e && Mask[i] != 2*e) {
Mask[i] = 2*e;
MadeChange = true;
}
}
if (MadeChange) {
// Remap any references to RHS to use LHS.
std::vector<Constant*> Elts;
for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
if (Mask[i] == 2*e)
Elts.push_back(UndefValue::get(Type::Int32Ty));
else
Elts.push_back(ConstantInt::get(Type::Int32Ty, Mask[i]));
}
SVI.setOperand(2, ConstantVector::get(Elts));
}
}
uint64_t UndefElts;
unsigned VWidth = cast<VectorType>(SVI.getType())->getNumElements();
uint64_t AllOnesEltMask = ~0ULL >> (64-VWidth);
if (VWidth <= 64 &&
SimplifyDemandedVectorElts(&SVI, AllOnesEltMask, UndefElts))
MadeChange = true;
// Canonicalize shuffle(x ,x,mask) -> shuffle(x, undef,mask')
// Canonicalize shuffle(undef,x,mask) -> shuffle(x, undef,mask').

33
llvm/test/Transforms/InstCombine/pr2645.ll Normal file
View File

@ -0,0 +1,33 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {insertelement <4 x float> undef}
; Instcombine should be able to prove that none of the
; insertelement's first operand's elements are needed.
define internal void @""(i8*) {
; <label>:1
bitcast i8* %0 to i32* ; <i32*>:2 [#uses=1]
load i32* %2, align 1 ; <i32>:3 [#uses=1]
getelementptr i8* %0, i32 4 ; <i8*>:4 [#uses=1]
bitcast i8* %4 to i32* ; <i32*>:5 [#uses=1]
load i32* %5, align 1 ; <i32>:6 [#uses=1]
br label %7
; <label>:7 ; preds = %9, %1
%.01 = phi <4 x float> [ undef, %1 ], [ %12, %9 ] ; <<4 x float>> [#uses=1]
%.0 = phi i32 [ %3, %1 ], [ %15, %9 ] ; <i32> [#uses=3]
icmp slt i32 %.0, %6 ; <i1>:8 [#uses=1]
br i1 %8, label %9, label %16
; <label>:9 ; preds = %7
sitofp i32 %.0 to float ; <float>:10 [#uses=1]
insertelement <4 x float> %.01, float %10, i32 0 ; <<4 x float>>:11 [#uses=1]
shufflevector <4 x float> %11, <4 x float> undef, <4 x i32> zeroinitializer ; <<4 x float>>:12 [#uses=2]
getelementptr i8* %0, i32 48 ; <i8*>:13 [#uses=1]
bitcast i8* %13 to <4 x float>* ; <<4 x float>*>:14 [#uses=1]
store <4 x float> %12, <4 x float>* %14, align 16
add i32 %.0, 2 ; <i32>:15 [#uses=1]
br label %7
; <label>:16 ; preds = %7
ret void
}