[OPENMP] Fix use of unsigned counters in loops with zero trip count.
Patch fixes bugs in codegen for loops with unsigned counters and zero trip count. Previously preconditions for all loops were built using logic (Upper - Lower) > 0. But if the loop is a loop with zero trip count, then Upper - Lower is < 0 only for signed integer, for unsigned we're running into an underflow situation.
In this patch we're using original Lower<Upper condition to check that loop body can be executed at least once. Also this allows to skip code generation for loops, if it is known that preconditions for the loop are always false.
Differential Revision: http://reviews.llvm.org/D9103
llvm-svn: 235500
diff --git a/clang/lib/Sema/SemaOpenMP.cpp b/clang/lib/Sema/SemaOpenMP.cpp
index fed0ac7..0cfb94e 100644
--- a/clang/lib/Sema/SemaOpenMP.cpp
+++ b/clang/lib/Sema/SemaOpenMP.cpp
@@ -1977,6 +1977,8 @@
bool ShouldSubtractStep() const { return SubtractStep; }
/// \brief Build the expression to calculate the number of iterations.
Expr *BuildNumIterations(Scope *S, const bool LimitedType) const;
+ /// \brief Build the precondition expression for the loops.
+ Expr *BuildPreCond(Scope *S, Expr *Cond) const;
/// \brief Build reference expression to the counter be used for codegen.
Expr *BuildCounterVar() const;
/// \brief Build initization of the counter be used for codegen.
@@ -2380,6 +2382,19 @@
return Diff.get();
}
+Expr *OpenMPIterationSpaceChecker::BuildPreCond(Scope *S, Expr *Cond) const {
+ // Try to build LB <op> UB, where <op> is <, >, <=, or >=.
+ bool Suppress = SemaRef.getDiagnostics().getSuppressAllDiagnostics();
+ SemaRef.getDiagnostics().setSuppressAllDiagnostics(/*Val=*/true);
+ auto CondExpr = SemaRef.BuildBinOp(
+ S, DefaultLoc, TestIsLessOp ? (TestIsStrictOp ? BO_LT : BO_LE)
+ : (TestIsStrictOp ? BO_GT : BO_GE),
+ LB, UB);
+ SemaRef.getDiagnostics().setSuppressAllDiagnostics(Suppress);
+ // Otherwise use original loop conditon and evaluate it in runtime.
+ return CondExpr.isUsable() ? CondExpr.get() : Cond;
+}
+
/// \brief Build reference expression to the counter be used for codegen.
Expr *OpenMPIterationSpaceChecker::BuildCounterVar() const {
return DeclRefExpr::Create(SemaRef.Context, NestedNameSpecifierLoc(),
@@ -2395,6 +2410,8 @@
/// \brief Iteration space of a single for loop.
struct LoopIterationSpace {
+ /// \brief Condition of the loop.
+ Expr *PreCond;
/// \brief This expression calculates the number of iterations in the loop.
/// It is always possible to calculate it before starting the loop.
Expr *NumIterations;
@@ -2535,6 +2552,7 @@
return HasErrors;
// Build the loop's iteration space representation.
+ ResultIterSpace.PreCond = ISC.BuildPreCond(DSA.getCurScope(), For->getCond());
ResultIterSpace.NumIterations = ISC.BuildNumIterations(
DSA.getCurScope(), /* LimitedType */ isOpenMPWorksharingDirective(DKind));
ResultIterSpace.CounterVar = ISC.BuildCounterVar();
@@ -2545,7 +2563,8 @@
ResultIterSpace.IncSrcRange = ISC.GetIncrementSrcRange();
ResultIterSpace.Subtract = ISC.ShouldSubtractStep();
- HasErrors |= (ResultIterSpace.NumIterations == nullptr ||
+ HasErrors |= (ResultIterSpace.PreCond == nullptr ||
+ ResultIterSpace.NumIterations == nullptr ||
ResultIterSpace.CounterVar == nullptr ||
ResultIterSpace.CounterInit == nullptr ||
ResultIterSpace.CounterStep == nullptr);
@@ -2690,6 +2709,9 @@
// Last iteration number is (I1 * I2 * ... In) - 1, where I1, I2 ... In are
// the iteration counts of the collapsed for loops.
+ // Precondition tests if there is at least one iteration (all conditions are
+ // true).
+ auto PreCond = ExprResult(IterSpaces[0].PreCond);
auto N0 = IterSpaces[0].NumIterations;
ExprResult LastIteration32 = WidenIterationCount(32 /* Bits */, N0, SemaRef);
ExprResult LastIteration64 = WidenIterationCount(64 /* Bits */, N0, SemaRef);
@@ -2702,6 +2724,10 @@
Scope *CurScope = DSA.getCurScope();
for (unsigned Cnt = 1; Cnt < NestedLoopCount; ++Cnt) {
+ if (PreCond.isUsable()) {
+ PreCond = SemaRef.BuildBinOp(CurScope, SourceLocation(), BO_LAnd,
+ PreCond.get(), IterSpaces[Cnt].PreCond);
+ }
auto N = IterSpaces[Cnt].NumIterations;
AllCountsNeedLessThan32Bits &= C.getTypeSize(N->getType()) < 32;
if (LastIteration32.isUsable())
@@ -2763,11 +2789,6 @@
SourceLocation InitLoc = IterSpaces[0].InitSrcRange.getBegin();
- // Precondition tests if there is at least one iteration (LastIteration > 0).
- ExprResult PreCond = SemaRef.BuildBinOp(
- CurScope, InitLoc, BO_GT, LastIteration.get(),
- SemaRef.ActOnIntegerConstant(SourceLocation(), 0).get());
-
QualType VType = LastIteration.get()->getType();
// Build variables passed into runtime, nesessary for worksharing directives.
ExprResult LB, UB, IL, ST, EUB;