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Check for overflow when scaling up an add or an addrec for

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scaled reuse.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96692 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2010-02-19 19:32:49 +00:00
parent 1a2e8686f8
commit aae01f17a6
2 changed files with 86 additions and 18 deletions
lib/Transforms/Scalar
LoopStrengthReduce.cpp
test/CodeGen/X86
lsr-wrap.ll

67
lib/Transforms/Scalar/LoopStrengthReduce.cpp

@ -337,6 +337,33 @@ void Formula::dump() const {
print(errs()); errs() << '\n';
}
/// isAddRecSExtable - Return true if the given addrec can be sign-extended
/// without changing its value.
static bool isAddRecSExtable(const SCEVAddRecExpr *AR, ScalarEvolution &SE) {
const Type *WideTy =
IntegerType::get(SE.getContext(),
SE.getTypeSizeInBits(AR->getType()) + 1);
return isa<SCEVAddRecExpr>(SE.getSignExtendExpr(AR, WideTy));
}
/// isAddSExtable - Return true if the given add can be sign-extended
/// without changing its value.
static bool isAddSExtable(const SCEVAddExpr *A, ScalarEvolution &SE) {
const Type *WideTy =
IntegerType::get(SE.getContext(),
SE.getTypeSizeInBits(A->getType()) + 1);
return isa<SCEVAddExpr>(SE.getSignExtendExpr(A, WideTy));
}
/// isMulSExtable - Return true if the given add can be sign-extended
/// without changing its value.
static bool isMulSExtable(const SCEVMulExpr *A, ScalarEvolution &SE) {
const Type *WideTy =
IntegerType::get(SE.getContext(),
SE.getTypeSizeInBits(A->getType()) + 1);
return isa<SCEVMulExpr>(SE.getSignExtendExpr(A, WideTy));
}
/// getSDiv - Return an expression for LHS /s RHS, if it can be determined,
/// or null otherwise. If IgnoreSignificantBits is true, expressions like
/// (X * Y) /s Y are simplified to Y, ignoring that the multiplication may
@ -365,33 +392,37 @@ static const SCEV *getSDiv(const SCEV *LHS, const SCEV *RHS,
.sdiv(RC->getValue()->getValue()));
}
// Distribute the sdiv over addrec operands.
// Distribute the sdiv over addrec operands, if the addrec doesn't overflow.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS)) {
const SCEV *Start = getSDiv(AR->getStart(), RHS, SE,
IgnoreSignificantBits);
if (!Start) return 0;
const SCEV *Step = getSDiv(AR->getStepRecurrence(SE), RHS, SE,
IgnoreSignificantBits);
if (!Step) return 0;
return SE.getAddRecExpr(Start, Step, AR->getLoop());
if (IgnoreSignificantBits || isAddRecSExtable(AR, SE)) {
const SCEV *Start = getSDiv(AR->getStart(), RHS, SE,
IgnoreSignificantBits);
if (!Start) return 0;
const SCEV *Step = getSDiv(AR->getStepRecurrence(SE), RHS, SE,
IgnoreSignificantBits);
if (!Step) return 0;
return SE.getAddRecExpr(Start, Step, AR->getLoop());
}
}
// Distribute the sdiv over add operands.
// Distribute the sdiv over add operands, if the add doesn't overflow.
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(LHS)) {
SmallVector<const SCEV *, 8> Ops;
for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
I != E; ++I) {
const SCEV *Op = getSDiv(*I, RHS, SE,
IgnoreSignificantBits);
if (!Op) return 0;
Ops.push_back(Op);
if (IgnoreSignificantBits || isAddSExtable(Add, SE)) {
SmallVector<const SCEV *, 8> Ops;
for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
I != E; ++I) {
const SCEV *Op = getSDiv(*I, RHS, SE,
IgnoreSignificantBits);
if (!Op) return 0;
Ops.push_back(Op);
}
return SE.getAddExpr(Ops);
}
return SE.getAddExpr(Ops);
}
// Check for a multiply operand that we can pull RHS out of.
if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(LHS))
if (IgnoreSignificantBits || Mul->hasNoSignedWrap()) {
if (IgnoreSignificantBits || isMulSExtable(Mul, SE)) {
SmallVector<const SCEV *, 4> Ops;
bool Found = false;
for (SCEVMulExpr::op_iterator I = Mul->op_begin(), E = Mul->op_end();

37
test/CodeGen/X86/lsr-wrap.ll Normal file

@ -0,0 +1,37 @@
; RUN: llc -march=x86-64 < %s | FileCheck %s
; LSR would like to use a single IV for both of these, however it's
; not safe due to wraparound.
; CHECK: addb $-4, %r
; CHECK: decw %
@g_19 = common global i32 0 ; <i32*> [#uses=2]
declare i32 @func_8(i8 zeroext) nounwind
declare i32 @func_3(i8 signext) nounwind
define void @func_1() nounwind {
entry:
br label %bb
bb: ; preds = %bb, %entry
%indvar = phi i16 [ 0, %entry ], [ %indvar.next, %bb ] ; <i16> [#uses=2]
%tmp = sub i16 0, %indvar ; <i16> [#uses=1]
%tmp27 = trunc i16 %tmp to i8 ; <i8> [#uses=1]
%tmp1 = load i32* @g_19, align 4 ; <i32> [#uses=2]
%tmp2 = add i32 %tmp1, 1 ; <i32> [#uses=1]
store i32 %tmp2, i32* @g_19, align 4
%tmp3 = trunc i32 %tmp1 to i8 ; <i8> [#uses=1]
%tmp4 = tail call i32 @func_8(i8 zeroext %tmp3) nounwind ; <i32> [#uses=0]
%tmp5 = shl i8 %tmp27, 2 ; <i8> [#uses=1]
%tmp6 = add i8 %tmp5, -112 ; <i8> [#uses=1]
%tmp7 = tail call i32 @func_3(i8 signext %tmp6) nounwind ; <i32> [#uses=0]
%indvar.next = add i16 %indvar, 1 ; <i16> [#uses=2]
%exitcond = icmp eq i16 %indvar.next, -28 ; <i1> [#uses=1]
br i1 %exitcond, label %return, label %bb
return: ; preds = %bb
ret void
}