AArch64/PowerPC/SystemZ/X86: This patch fixes the interface, usage, and all

in-tree implementations of TargetLoweringBase::isFMAFasterThanMulAndAdd in
order to resolve the following issues with fmuladd (i.e. optional FMA)
intrinsics:

1. On X86(-64) targets, ISD::FMA nodes are formed when lowering fmuladd
intrinsics even if the subtarget does not support FMA instructions, leading
to laughably bad code generation in some situations.

2. On AArch64 targets, ISD::FMA nodes are formed for operations on fp128,
resulting in a call to a software fp128 FMA implementation.

3. On PowerPC targets, FMAs are not generated from fmuladd intrinsics on types
like v2f32, v8f32, v4f64, etc., even though they promote, split, scalarize,
etc. to types that support hardware FMAs.

The function has also been slightly renamed for consistency and to force a
merge/build conflict for any out-of-tree target implementing it. To resolve,
see comments and fixed in-tree examples.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185956 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 10 insertions, 5 deletions

diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index 70b285e..d1c98f6 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -1213,11 +1213,16 @@ public:
     return false;
   }
 
-  /// isFMAFasterThanMulAndAdd - Return true if an FMA operation is faster than
-  /// a pair of mul and add instructions. fmuladd intrinsics will be expanded to
-  /// FMAs when this method returns true (and FMAs are legal), otherwise fmuladd
-  /// is expanded to mul + add.
-  virtual bool isFMAFasterThanMulAndAdd(EVT) const {
+  /// isFMAFasterThanFMulAndFAdd - Return true if an FMA operation is faster
+  /// than a pair of fmul and fadd instructions. fmuladd intrinsics will be
+  /// expanded to FMAs when this method returns true, otherwise fmuladd is
+  /// expanded to fmul + fadd.
+  ///
+  /// NOTE: This may be called before legalization on types for which FMAs are
+  /// not legal, but should return true if those types will eventually legalize
+  /// to types that support FMAs. After legalization, it will only be called on
+  /// types that support FMAs (via Legal or Custom actions)
+  virtual bool isFMAFasterThanFMulAndFAdd(EVT) const {
     return false;
   }