Take math-errno into account with '#pragma float_control(precise,on)' and

'attribute__((optnone)).

Differential Revision: https://reviews.llvm.org/D151834

3 files changed, 77 insertions, 4 deletions

diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index a513eae..5f9199d 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -2312,6 +2312,26 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
   const unsigned BuiltinIDIfNoAsmLabel =
       FD->hasAttr<AsmLabelAttr>() ? 0 : BuiltinID;
 
+  bool ErrnoOverriden = false;
+  // True if math-errno is overriden via the
+  // '#pragma float_control(precise, on)'. This pragma disables fast-math,
+  // which implies math-errno.
+  if (E->hasStoredFPFeatures()) {
+    FPOptionsOverride OP = E->getFPFeatures();
+    if (OP.hasMathErrnoOverride())
+      ErrnoOverriden = OP.getMathErrnoOverride();
+  }
+  // True if 'atttibute__((optnone)) is used. This attibute overrides
+  // fast-math which implies math-errno.
+  bool OptNone = CurFuncDecl && CurFuncDecl->hasAttr<OptimizeNoneAttr>();
+
+  // True if we are compiling at -O2 and errno has been disabled
+  // using the '#pragma float_control(precise, off)', and
+  // attribute opt-none hasn't been seen.
+  bool ErrnoOverridenToFalseWithOpt =
+      !ErrnoOverriden && !OptNone &&
+      CGM.getCodeGenOpts().OptimizationLevel != 0;
+
   // There are LLVM math intrinsics/instructions corresponding to math library
   // functions except the LLVM op will never set errno while the math library
   // might. Also, math builtins have the same semantics as their math library
@@ -2323,9 +2343,38 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
       getContext().BuiltinInfo.isConstWithoutErrnoAndExceptions(BuiltinID);
   bool ConstWithoutExceptions =
       getContext().BuiltinInfo.isConstWithoutExceptions(BuiltinID);
-  if (FD->hasAttr<ConstAttr>() ||
-      ((ConstWithoutErrnoAndExceptions || ConstWithoutExceptions) &&
-       (!ConstWithoutErrnoAndExceptions || (!getLangOpts().MathErrno)))) {
+
+  // ConstAttr is enabled in fast-math mode. In fast-math mode, math-errno is
+  // disabled.
+  // Math intrinsics are generated only when math-errno is disabled. Any pragmas
+  // or attributes that affect math-errno should prevent or allow math
+  // intrincs to be generated. Intrinsics are generated:
+  //   1- In fast math mode, unless math-errno is overriden
+  //      via '#pragma float_control(precise, on)', or via an
+  //      'attribute__((optnone))'.
+  //   2- If math-errno was enabled on command line but overriden
+  //      to false via '#pragma float_control(precise, off))' and
+  //      'attribute__((optnone))' hasn't been used.
+  //   3- If we are compiling with optimization and errno has been disabled
+  //      via '#pragma float_control(precise, off)', and
+  //      'attribute__((optnone))' hasn't been used.
+
+  bool ConstWithoutErrnoOrExceptions =
+      ConstWithoutErrnoAndExceptions || ConstWithoutExceptions;
+  bool GenerateIntrinsics =
+      FD->hasAttr<ConstAttr>() && !ErrnoOverriden && !OptNone;
+  if (!GenerateIntrinsics) {
+    GenerateIntrinsics =
+        ConstWithoutErrnoOrExceptions && !ConstWithoutErrnoAndExceptions;
+    if (!GenerateIntrinsics)
+      GenerateIntrinsics =
+          ConstWithoutErrnoOrExceptions &&
+          (!getLangOpts().MathErrno && !ErrnoOverriden && !OptNone);
+    if (!GenerateIntrinsics)
+      GenerateIntrinsics =
+          ConstWithoutErrnoOrExceptions && ErrnoOverridenToFalseWithOpt;
+  }
+  if (GenerateIntrinsics) {
     switch (BuiltinIDIfNoAsmLabel) {
     case Builtin::BIceil:
     case Builtin::BIceilf:
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 37de280..e15a463 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -2279,6 +2279,17 @@ static llvm::FPClassTest getNoFPClassTestMask(const LangOptions &LangOpts) {
   return Mask;
 }
 
+void CodeGenModule::AdjustMemoryAttribute(StringRef Name,
+                                          CGCalleeInfo CalleeInfo,
+                                          llvm::AttributeList &Attrs) {
+  if (Attrs.getMemoryEffects().getModRef() == llvm::ModRefInfo::NoModRef) {
+    Attrs = Attrs.removeFnAttribute(getLLVMContext(), llvm::Attribute::Memory);
+    llvm::Attribute MemoryAttr = llvm::Attribute::getWithMemoryEffects(
+        getLLVMContext(), llvm::MemoryEffects::writeOnly());
+    Attrs = Attrs.addFnAttribute(getLLVMContext(), MemoryAttr);
+  }
+}
+
 /// Construct the IR attribute list of a function or call.
 ///
 /// When adding an attribute, please consider where it should be handled:
@@ -5501,11 +5512,18 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
                              /*AttrOnCallSite=*/true,
                              /*IsThunk=*/false);
 
-  if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(CurFuncDecl))
+  if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(CurFuncDecl)) {
     if (FD->hasAttr<StrictFPAttr>())
       // All calls within a strictfp function are marked strictfp
       Attrs = Attrs.addFnAttribute(getLLVMContext(), llvm::Attribute::StrictFP);
 
+    // If -ffast-math is enabled and the function is guarded by an
+    // '__attribute__((optnone)) adjust the memory attribute so the BE emits the
+    // library call instead of the intrinsic.
+    if (FD->hasAttr<OptimizeNoneAttr>() && getLangOpts().FastMath)
+      CGM.AdjustMemoryAttribute(CalleePtr->getName(), Callee.getAbstractInfo(),
+                                Attrs);
+  }
   // Add call-site nomerge attribute if exists.
   if (InNoMergeAttributedStmt)
     Attrs = Attrs.addFnAttribute(getLLVMContext(), llvm::Attribute::NoMerge);
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 79f48b6..073b471 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -1260,6 +1260,12 @@ public:
                               llvm::AttributeList &Attrs, unsigned &CallingConv,
                               bool AttrOnCallSite, bool IsThunk);
 
+  /// Adjust Memory attribute to ensure that the BE gets the right attribute
+  // in order to generate the library call or the intrinsic for the function
+  // name 'Name'.
+  void AdjustMemoryAttribute(StringRef Name, CGCalleeInfo CalleeInfo,
+                             llvm::AttributeList &Attrs);
+
   /// Like the overload taking a `Function &`, but intended specifically
   /// for frontends that want to build on Clang's target-configuration logic.
   void addDefaultFunctionDefinitionAttributes(llvm::AttrBuilder &attrs);