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Scalar shifts in the OpenCL specification (as of v. 1.2) are defined to be 

with respect to the lower "left-hand-side bitwidth" bits, even when negative);
see OpenCL spec 6.3j. This patch both implements this behaviour in the code
generator and "constant folding" bits of Sema, and also prevents tests
to detect undefinedness in terms of the weaker C99 or C++ specifications
from being applied. 

llvm-svn: 171755
This commit is contained in:
David Tweed 2013-01-07 16:43:27 +00:00
parent d5650bdc1a
commit 042e0883cb
6 changed files with 84 additions and 18 deletions
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22
clang/lib/AST/ExprConstant.cpp
View File

@ -4708,9 +4708,14 @@ bool DataRecursiveIntBinOpEvaluator::
return Success(E->getOpcode() == BO_Rem ? LHS % RHS : LHS / RHS, E,
Result);
case BO_Shl: {
// During constant-folding, a negative shift is an opposite shift. Such
// a shift is not a constant expression.
if (RHS.isSigned() && RHS.isNegative()) {
if (Info.getLangOpts().OpenCL)
// OpenCL 6.3j: shift values are effectively % word size of LHS.
RHS &= APSInt(llvm::APInt(LHS.getBitWidth(),
static_cast<uint64_t>(LHS.getBitWidth() - 1)),
RHS.isUnsigned());
else if (RHS.isSigned() && RHS.isNegative()) {
// During constant-folding, a negative shift is an opposite shift. Such
// a shift is not a constant expression.
CCEDiag(E, diag::note_constexpr_negative_shift) << RHS;
RHS = -RHS;
goto shift_right;
@ -4735,9 +4740,14 @@ bool DataRecursiveIntBinOpEvaluator::
return Success(LHS << SA, E, Result);
}
case BO_Shr: {
// During constant-folding, a negative shift is an opposite shift. Such a
// shift is not a constant expression.
if (RHS.isSigned() && RHS.isNegative()) {
if (Info.getLangOpts().OpenCL)
// OpenCL 6.3j: shift values are effectively % word size of LHS.
RHS &= APSInt(llvm::APInt(LHS.getBitWidth(),
static_cast<uint64_t>(LHS.getBitWidth() - 1)),
RHS.isUnsigned());
else if (RHS.isSigned() && RHS.isNegative()) {
// During constant-folding, a negative shift is an opposite shift. Such a
// shift is not a constant expression.
CCEDiag(E, diag::note_constexpr_negative_shift) << RHS;
RHS = -RHS;
goto shift_left;

31
clang/lib/CodeGen/CGExprScalar.cpp
View File

@ -429,6 +429,8 @@ public:
// Check for undefined division and modulus behaviors.
void EmitUndefinedBehaviorIntegerDivAndRemCheck(const BinOpInfo &Ops,
llvm::Value *Zero,bool isDiv);
// Common helper for getting how wide LHS of shift is.
static Value *GetWidthMinusOneValue(Value* LHS,Value* RHS);
Value *EmitDiv(const BinOpInfo &Ops);
Value *EmitRem(const BinOpInfo &Ops);
Value *EmitAdd(const BinOpInfo &Ops);
@ -2365,6 +2367,11 @@ Value *ScalarExprEmitter::EmitSub(const BinOpInfo &op) {
return Builder.CreateExactSDiv(diffInChars, divisor, "sub.ptr.div");
}
Value *ScalarExprEmitter::GetWidthMinusOneValue(Value* LHS,Value* RHS) {
unsigned Width = cast<llvm::IntegerType>(LHS->getType())->getBitWidth();
return llvm::ConstantInt::get(RHS->getType(), Width - 1);
}
Value *ScalarExprEmitter::EmitShl(const BinOpInfo &Ops) {
// LLVM requires the LHS and RHS to be the same type: promote or truncate the
// RHS to the same size as the LHS.
@ -2372,11 +2379,9 @@ Value *ScalarExprEmitter::EmitShl(const BinOpInfo &Ops) {
if (Ops.LHS->getType() != RHS->getType())
RHS = Builder.CreateIntCast(RHS, Ops.LHS->getType(), false, "sh_prom");
if (CGF.getLangOpts().SanitizeShift &&
isa<llvm::IntegerType>(Ops.LHS->getType())) {
unsigned Width = cast<llvm::IntegerType>(Ops.LHS->getType())->getBitWidth();
llvm::Value *WidthMinusOne =
llvm::ConstantInt::get(RHS->getType(), Width - 1);
if (CGF.getLangOpts().SanitizeShift && !CGF.getLangOpts().OpenCL
&& isa<llvm::IntegerType>(Ops.LHS->getType())) {
llvm::Value *WidthMinusOne = GetWidthMinusOneValue(Ops.LHS, RHS);
// FIXME: Emit the branching explicitly rather than emitting the check
// twice.
EmitBinOpCheck(Builder.CreateICmpULE(RHS, WidthMinusOne), Ops);
@ -2401,6 +2406,9 @@ Value *ScalarExprEmitter::EmitShl(const BinOpInfo &Ops) {
EmitBinOpCheck(Builder.CreateICmpEQ(BitsShiftedOff, Zero), Ops);
}
}
// OpenCL 6.3j: shift values are effectively % word size of LHS.
if (CGF.getLangOpts().OpenCL)
RHS = Builder.CreateAnd(RHS, GetWidthMinusOneValue(Ops.LHS, RHS), "shl.mask");
return Builder.CreateShl(Ops.LHS, RHS, "shl");
}
@ -2412,12 +2420,13 @@ Value *ScalarExprEmitter::EmitShr(const BinOpInfo &Ops) {
if (Ops.LHS->getType() != RHS->getType())
RHS = Builder.CreateIntCast(RHS, Ops.LHS->getType(), false, "sh_prom");
if (CGF.getLangOpts().SanitizeShift &&
isa<llvm::IntegerType>(Ops.LHS->getType())) {
unsigned Width = cast<llvm::IntegerType>(Ops.LHS->getType())->getBitWidth();
llvm::Value *WidthVal = llvm::ConstantInt::get(RHS->getType(), Width);
EmitBinOpCheck(Builder.CreateICmpULT(RHS, WidthVal), Ops);
}
if (CGF.getLangOpts().SanitizeShift && !CGF.getLangOpts().OpenCL
&& isa<llvm::IntegerType>(Ops.LHS->getType()))
EmitBinOpCheck(Builder.CreateICmpULE(RHS, GetWidthMinusOneValue(Ops.LHS, RHS)), Ops);
// OpenCL 6.3j: shift values are effectively % word size of LHS.
if (CGF.getLangOpts().OpenCL)
RHS = Builder.CreateAnd(RHS, GetWidthMinusOneValue(Ops.LHS, RHS), "shr.mask");
if (Ops.Ty->hasUnsignedIntegerRepresentation())
return Builder.CreateLShr(Ops.LHS, RHS, "shr");

5
clang/lib/Sema/SemaExpr.cpp
View File

@ -6578,6 +6578,11 @@ static bool isScopedEnumerationType(QualType T) {
static void DiagnoseBadShiftValues(Sema& S, ExprResult &LHS, ExprResult &RHS,
SourceLocation Loc, unsigned Opc,
QualType LHSType) {
// OpenCL 6.3j: shift values are effectively % word size of LHS (more defined),
// so skip remaining warnings as we don't want to modify values within Sema.
if (S.getLangOpts().OpenCL)
return;
llvm::APSInt Right;
// Check right/shifter operand
if (RHS.get()->isValueDependent() ||

2
clang/test/CodeGen/catch-undef-behavior.c
View File

@ -99,7 +99,7 @@ int lsh_overflow(int a, int b) {
// CHECK: @rsh_inbounds
int rsh_inbounds(int a, int b) {
// CHECK: %[[INBOUNDS:.*]] = icmp ult i32 %[[RHS:.*]], 32
// CHECK: %[[INBOUNDS:.*]] = icmp ule i32 %[[RHS:.*]], 31
// CHECK: br i1 %[[INBOUNDS]]
// CHECK: %[[ARG1:.*]] = zext

28
clang/test/CodeGenOpenCL/shifts.cl Normal file
View File

@ -0,0 +1,28 @@
// RUN: %clang_cc1 -x cl -O1 -emit-llvm %s -o - -triple x86_64-linux-gnu | FileCheck %s
// OpenCL essentially reduces all shift amounts to the last word-size bits before evaluating.
// Test this both for variables and constants evaluated in the front-end.
//CHECK: @positiveShift32
int positiveShift32(int a,int b) {
//CHECK: %shl.mask = and i32 %b, 31
//CHECK-NEXT: %shl = shl i32 %a, %shl.mask
int c = a<<b;
int d = ((int)1)<<33;
//CHECK-NEXT: %add = add nsw i32 %shl, 2
int e = c + d;
//CHECK-NEXT: ret i32 %add
return e;
}
//CHECK: @positiveShift64
long positiveShift64(long a,long b) {
//CHECK: %shr.mask = and i64 %b, 63
//CHECK-NEXT: %shr = ashr i64 %a, %shr.mask
long c = a>>b;
long d = ((long)8)>>65;
//CHECK-NEXT: %add = add nsw i64 %shr, 4
long e = c + d;
//CHECK-NEXT: ret i64 %add
return e;
}

14
clang/test/Sema/shiftOpenCL.cl Normal file
View File

@ -0,0 +1,14 @@
// RUN: %clang_cc1 -x cl -O1 -emit-llvm %s -o - -triple x86_64-linux-gnu | FileCheck %s
// OpenCL essentially reduces all shift amounts to the last word-size bits before evaluating.
// Test this both for variables and constants evaluated in the front-end.
//CHECK: @array0 = common global [256 x i8]
char array0[((int)1)<<40];
//CHECK: @array1 = common global [256 x i8]
char array1[((int)1)<<(-24)];
//CHECK: @negativeShift32
int negativeShift32(int a,int b) {
//CHECK: ret i32 65536
return ((int)1)<<(-16);
}