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

clang/lib/AST/ExprConstant.cpp

@@ -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;

clang/lib/CodeGen/CGExprScalar.cpp

@@ -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");

clang/lib/Sema/SemaExpr.cpp

@@ -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() ||

clang/test/CodeGen/catch-undef-behavior.c

@@ -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

clang/test/CodeGenOpenCL/shifts.cl

@@ -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;
+}

clang/test/Sema/shiftOpenCL.cl

@@ -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);
+}