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Fix bogus overflow checks by replacing them with actual 

overflow checks.

llvm-svn: 71284
This commit is contained in:
Dan Gohman 2009-05-08 23:11:16 +00:00
parent 884a8996c5
commit 35dc9b65ed
2 changed files with 28 additions and 7 deletions
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25
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -1381,29 +1381,39 @@ SCEVHandle ScalarEvolution::getUDivExpr(const SCEVHandle &LHS,
dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this)))
if (!Step->getValue()->getValue()
.urem(RHSC->getValue()->getValue()) &&
getTruncateExpr(getZeroExtendExpr(AR, ExtTy), Ty) == AR) {
getZeroExtendExpr(AR, ExtTy) ==
getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy),
getZeroExtendExpr(Step, ExtTy),
AR->getLoop())) {
std::vector<SCEVHandle> Operands;
for (unsigned i = 0, e = AR->getNumOperands(); i != e; ++i)
Operands.push_back(getUDivExpr(AR->getOperand(i), RHS));
return getAddRecExpr(Operands, AR->getLoop());
}
// (A*B)/C --> A*(B/C) if safe and B/C can be folded.
if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(LHS))
if (getTruncateExpr(getZeroExtendExpr(M, ExtTy), Ty) == M)
if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(LHS)) {
std::vector<SCEVHandle> Operands;
for (unsigned i = 0, e = M->getNumOperands(); i != e; ++i)
Operands.push_back(getZeroExtendExpr(M->getOperand(i), ExtTy));
if (getZeroExtendExpr(M, ExtTy) == getMulExpr(Operands))
// Find an operand that's safely divisible.
for (unsigned i = 0, e = M->getNumOperands(); i != e; ++i) {
SCEVHandle Op = M->getOperand(i);
SCEVHandle Div = getUDivExpr(Op, RHSC);
if (!isa<SCEVUDivExpr>(Div) && getMulExpr(Div, RHSC) == Op) {
std::vector<SCEVHandle> Operands = M->getOperands();
Operands = M->getOperands();
Operands[i] = Div;
return getMulExpr(Operands);
}
}
}
// (A+B)/C --> (A/C + B/C) if safe and A/C and B/C can be folded.
if (const SCEVAddRecExpr *A = dyn_cast<SCEVAddRecExpr>(LHS))
if (getTruncateExpr(getZeroExtendExpr(A, ExtTy), Ty) == A) {
std::vector<SCEVHandle> Operands;
if (const SCEVAddRecExpr *A = dyn_cast<SCEVAddRecExpr>(LHS)) {
std::vector<SCEVHandle> Operands;
for (unsigned i = 0, e = A->getNumOperands(); i != e; ++i)
Operands.push_back(getZeroExtendExpr(A->getOperand(i), ExtTy));
if (getZeroExtendExpr(A, ExtTy) == getAddExpr(Operands)) {
Operands.clear();
for (unsigned i = 0, e = A->getNumOperands(); i != e; ++i) {
SCEVHandle Op = getUDivExpr(A->getOperand(i), RHS);
if (isa<SCEVUDivExpr>(Op) || getMulExpr(Op, RHS) != A->getOperand(i))
@ -1413,6 +1423,7 @@ SCEVHandle ScalarEvolution::getUDivExpr(const SCEVHandle &LHS,
if (Operands.size() == A->getNumOperands())
return getAddExpr(Operands);
}
}
// Fold if both operands are constant.
if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS)) {

10
llvm/test/Analysis/ScalarEvolution/div-overflow.ll Normal file
View File

@ -0,0 +1,10 @@
; RUN: llvm-as < %s | opt -scalar-evolution -analyze -disable-output \
; RUN: | grep {\\--> ((-128 \\* %a) /u -128)}
; Don't let ScalarEvolution fold this div away.
define i8 @foo(i8 %a) {
%t0 = shl i8 %a, 7
%t1 = lshr i8 %t0, 7
ret i8 %t1
}