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

2 files changed, 26 insertions, 5 deletions

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index a680ac0..f00df35 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -12966,6 +12966,27 @@ bool X86TargetLowering::isZExtFree(SDValue Val, EVT VT2) const {
   return false;
 }
 
+bool
+X86TargetLowering::isFMAFasterThanFMulAndFAdd(EVT VT) const {
+  if (!(Subtarget->hasFMA() || Subtarget->hasFMA4()))
+    return false;
+
+  VT = VT.getScalarType();
+
+  if (!VT.isSimple())
+    return false;
+
+  switch (VT.getSimpleVT().SimpleTy) {
+  case MVT::f32:
+  case MVT::f64:
+    return true;
+  default:
+    break;
+  }
+
+  return false;
+}
+
 bool X86TargetLowering::isNarrowingProfitable(EVT VT1, EVT VT2) const {
   // i16 instructions are longer (0x66 prefix) and potentially slower.
   return !(VT1 == MVT::i32 && VT2 == MVT::i16);
diff --git a/lib/Target/X86/X86ISelLowering.h b/lib/Target/X86/X86ISelLowering.h
index 0e5e822..8317824 100644
--- a/lib/Target/X86/X86ISelLowering.h
+++ b/lib/Target/X86/X86ISelLowering.h
@@ -646,11 +646,11 @@ namespace llvm {
     virtual bool isZExtFree(EVT VT1, EVT VT2) const;
     virtual bool isZExtFree(SDValue Val, EVT VT2) const;
 
-    /// 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 { return true; }
+    /// 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.
+    virtual bool isFMAFasterThanFMulAndFAdd(EVT VT) const;
 
     /// isNarrowingProfitable - Return true if it's profitable to narrow
     /// operations of type VT1 to VT2. e.g. on x86, it's profitable to narrow