[complex] Teach Clang to preserve different-type operands to arithmetic

operators where one type is a C complex type, and to emit both the
efficient and correct implementation for complex arithmetic according to
C11 Annex G using this extra information.

For both multiply and divide the old code was writing a long-hand
reduced version of the math without any of the special handling of inf
and NaN recommended by the standard here. Instead of putting more
complexity here, this change does what GCC does which is to emit
a libcall for the fully general case.

However, the old code also failed to do the proper minimization of the
set of operations when there was a mixed complex and real operation. In
those cases, C provides a spec for much more minimal operations that are
valid. Clang now emits the exact suggested operations. This change isn't
*just* about performance though, without minimizing these operations, we
again lose the correct handling of infinities and NaNs. It is critical
that this happen in the frontend based on assymetric type operands to
complex math operations.

The performance implications of this change aren't trivial either. I've
run a set of benchmarks in Eigen, an open source mathematics library
that makes heavy use of complex. While a few have slowed down due to the
libcall being introduce, most sped up and some by a huge amount: up to
100% and 140%.

In order to make all of this work, also match the algorithm in the
constant evaluator to the one in the runtime library. Currently it is
a broken port of the simplifications from C's Annex G to the long-hand
formulation of the algorithm.

Splitting this patch up is very hard because none of this works without
the AST change to preserve non-complex operands. Sorry for the enormous
change.

Follow-up changes will include support for sinking the libcalls onto
cold paths in common cases and fastmath improvements to allow more
aggressive backend folding.

Differential Revision: http://reviews.llvm.org/D5698

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219557 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 29 insertions, 82 deletions

diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 4090953462..c0c074d316 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -938,68 +938,6 @@ static bool handleIntegerToComplexFloatConversion(Sema &S, ExprResult &IntExpr,
   return false;
 }
 
-/// \brief Takes two complex float types and converts them to the same type.
-/// Helper function of UsualArithmeticConversions()
-static QualType
-handleComplexFloatToComplexFloatConverstion(Sema &S, ExprResult &LHS,
-                                            ExprResult &RHS, QualType LHSType,
-                                            QualType RHSType,
-                                            bool IsCompAssign) {
-  int order = S.Context.getFloatingTypeOrder(LHSType, RHSType);
-
-  if (order < 0) {
-    // _Complex float -> _Complex double
-    if (!IsCompAssign)
-      LHS = S.ImpCastExprToType(LHS.get(), RHSType, CK_FloatingComplexCast);
-    return RHSType;
-  }
-  if (order > 0)
-    // _Complex float -> _Complex double
-    RHS = S.ImpCastExprToType(RHS.get(), LHSType, CK_FloatingComplexCast);
-  return LHSType;
-}
-
-/// \brief Converts otherExpr to complex float and promotes complexExpr if
-/// necessary.  Helper function of UsualArithmeticConversions()
-static QualType handleOtherComplexFloatConversion(Sema &S,
-                                                  ExprResult &ComplexExpr,
-                                                  ExprResult &OtherExpr,
-                                                  QualType ComplexTy,
-                                                  QualType OtherTy,
-                                                  bool ConvertComplexExpr,
-                                                  bool ConvertOtherExpr) {
-  int order = S.Context.getFloatingTypeOrder(ComplexTy, OtherTy);
-
-  // If just the complexExpr is complex, the otherExpr needs to be converted,
-  // and the complexExpr might need to be promoted.
-  if (order > 0) { // complexExpr is wider
-    // float -> _Complex double
-    if (ConvertOtherExpr) {
-      QualType fp = cast<ComplexType>(ComplexTy)->getElementType();
-      OtherExpr = S.ImpCastExprToType(OtherExpr.get(), fp, CK_FloatingCast);
-      OtherExpr = S.ImpCastExprToType(OtherExpr.get(), ComplexTy,
-                                      CK_FloatingRealToComplex);
-    }
-    return ComplexTy;
-  }
-
-  // otherTy is at least as wide.  Find its corresponding complex type.
-  QualType result = (order == 0 ? ComplexTy :
-                                  S.Context.getComplexType(OtherTy));
-
-  // double -> _Complex double
-  if (ConvertOtherExpr)
-    OtherExpr = S.ImpCastExprToType(OtherExpr.get(), result,
-                                    CK_FloatingRealToComplex);
-
-  // _Complex float -> _Complex double
-  if (ConvertComplexExpr && order < 0)
-    ComplexExpr = S.ImpCastExprToType(ComplexExpr.get(), result,
-                                      CK_FloatingComplexCast);
-
-  return result;
-}
-
 /// \brief Handle arithmetic conversion with complex types.  Helper function of
 /// UsualArithmeticConversions()
 static QualType handleComplexFloatConversion(Sema &S, ExprResult &LHS,
@@ -1025,26 +963,35 @@ static QualType handleComplexFloatConversion(Sema &S, ExprResult &LHS,
   // when combining a "long double" with a "double _Complex", the
   // "double _Complex" is promoted to "long double _Complex".
 
-  bool LHSComplexFloat = LHSType->isComplexType();
-  bool RHSComplexFloat = RHSType->isComplexType();
-
-  // If both are complex, just cast to the more precise type.
-  if (LHSComplexFloat && RHSComplexFloat)
-    return handleComplexFloatToComplexFloatConverstion(S, LHS, RHS,
-                                                       LHSType, RHSType,
-                                                       IsCompAssign);
-
-  // If only one operand is complex, promote it if necessary and convert the
-  // other operand to complex.
-  if (LHSComplexFloat)
-    return handleOtherComplexFloatConversion(
-        S, LHS, RHS, LHSType, RHSType, /*convertComplexExpr*/!IsCompAssign,
-        /*convertOtherExpr*/ true);
-
-  assert(RHSComplexFloat);
-  return handleOtherComplexFloatConversion(
-      S, RHS, LHS, RHSType, LHSType, /*convertComplexExpr*/true,
-      /*convertOtherExpr*/ !IsCompAssign);
+  // Compute the rank of the two types, regardless of whether they are complex.
+  int Order = S.Context.getFloatingTypeOrder(LHSType, RHSType);
+
+  auto *LHSComplexType = dyn_cast<ComplexType>(LHSType);
+  auto *RHSComplexType = dyn_cast<ComplexType>(RHSType);
+  QualType LHSElementType =
+      LHSComplexType ? LHSComplexType->getElementType() : LHSType;
+  QualType RHSElementType =
+      RHSComplexType ? RHSComplexType->getElementType() : RHSType;
+
+  QualType ResultType = S.Context.getComplexType(LHSElementType);
+  if (Order < 0) {
+    // Promote the precision of the LHS if not an assignment.
+    ResultType = S.Context.getComplexType(RHSElementType);
+    if (!IsCompAssign) {
+      if (LHSComplexType)
+        LHS =
+            S.ImpCastExprToType(LHS.get(), ResultType, CK_FloatingComplexCast);
+      else
+        LHS = S.ImpCastExprToType(LHS.get(), RHSElementType, CK_FloatingCast);
+    }
+  } else if (Order > 0) {
+    // Promote the precision of the RHS.
+    if (RHSComplexType)
+      RHS = S.ImpCastExprToType(RHS.get(), ResultType, CK_FloatingComplexCast);
+    else
+      RHS = S.ImpCastExprToType(RHS.get(), LHSElementType, CK_FloatingCast);
+  }
+  return ResultType;
 }
 
 /// \brief Hande arithmetic conversion from integer to float.  Helper function