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In the CBackend, use casts to force integer add, subtract, and

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multiply to be done as unsigned, so that they have well defined
behavior on overflow. This fixes PR2408.

llvm-svn: 53767
This commit is contained in:
Dan Gohman 2008-07-18 18:43:12 +00:00
parent e119f3db46
commit b97c076af4
3 changed files with 42 additions and 1 deletions
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28
lib/Target/CBackend/CBackend.cpp
View File

@ -1116,6 +1116,13 @@ bool CWriter::printConstExprCast(const ConstantExpr* CE) {
const Type *Ty = CE->getOperand(0)->getType();
bool TypeIsSigned = false;
switch (CE->getOpcode()) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
// We need to cast integer arithmetic so that it is always performed
// as unsigned, to avoid undefined behavior on overflow.
if (!Ty->isIntOrIntVector()) break;
// FALL THROUGH
case Instruction::LShr:
case Instruction::URem:
case Instruction::UDiv: NeedsExplicitCast = true; break;
@ -1174,6 +1181,13 @@ void CWriter::printConstantWithCast(Constant* CPV, unsigned Opcode) {
default:
// for most instructions, it doesn't matter
break;
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
// We need to cast integer arithmetic so that it is always performed
// as unsigned, to avoid undefined behavior on overflow.
if (!OpTy->isIntOrIntVector()) break;
// FALL THROUGH
case Instruction::LShr:
case Instruction::UDiv:
case Instruction::URem:
@ -1294,6 +1308,13 @@ void CWriter::writeOperand(Value *Operand) {
bool CWriter::writeInstructionCast(const Instruction &I) {
const Type *Ty = I.getOperand(0)->getType();
switch (I.getOpcode()) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
// We need to cast integer arithmetic so that it is always performed
// as unsigned, to avoid undefined behavior on overflow.
if (!Ty->isIntOrIntVector()) break;
// FALL THROUGH
case Instruction::LShr:
case Instruction::URem:
case Instruction::UDiv:
@ -1334,6 +1355,13 @@ void CWriter::writeOperandWithCast(Value* Operand, unsigned Opcode) {
default:
// for most instructions, it doesn't matter
break;
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
// We need to cast integer arithmetic so that it is always performed
// as unsigned, to avoid undefined behavior on overflow.
if (!OpTy->isIntOrIntVector()) break;
// FALL THROUGH
case Instruction::LShr:
case Instruction::UDiv:
case Instruction::URem: // Cast to unsigned first

3
test/CodeGen/CBackend/2007-02-23-NameConflicts.ll
View File

@ -1,7 +1,8 @@
; PR1164
; RUN: llvm-as < %s | llc -march=c | grep {llvm_cbe_A = \\*llvm_cbe_G;}
; RUN: llvm-as < %s | llc -march=c | grep {llvm_cbe_B = \\*(&ltmp_0_1);}
; RUN: llvm-as < %s | llc -march=c | grep {return (llvm_cbe_A + llvm_cbe_B);}
; RUN: llvm-as < %s | llc -march=c | grep {return (((unsigned int )(((unsigned int )llvm_cbe_A) + ((unsigned int )llvm_cbe_B))));}
@G = global i32 123
@ltmp_0_1 = global i32 123

12
test/CodeGen/CBackend/pr2408.ll Normal file
View File

@ -0,0 +1,12 @@
; RUN: llvm-as < %s | llc -march=c | grep {\\* ((unsigned int )}
; PR2408
define i32 @a(i32 %a) {
entry:
%shr = ashr i32 %a, 0 ; <i32> [#uses=1]
%shr2 = ashr i32 2, 0 ; <i32> [#uses=1]
%mul = mul i32 %shr, %shr2 ; <i32> [#uses=1]
%shr4 = ashr i32 2, 0 ; <i32> [#uses=1]
%div = sdiv i32 %mul, %shr4 ; <i32> [#uses=1]
ret i32 %div
}