[AArch64] Enable aggressive FMA on T99 and provide AArch64 options for others.

This patch enables aggressive FMA by default on T99, and provides a -mllvm
option to enable the same on other AArch64 micro-arch's (-mllvm
-aarch64-enable-aggressive-fma).

Test case demonstrating the effects on T99 is included.

Patch by: steleman (Stefan Teleman)

Differential Revision: https://reviews.llvm.org/D40696

llvm-svn: 323474

lib/Target/AArch64/AArch64.td

@@ -149,6 +149,12 @@ def FeatureLSLFast : SubtargetFeature<
     "lsl-fast", "HasLSLFast", "true",
     "CPU has a fastpath logical shift of up to 3 places">;
 
+def FeatureAggressiveFMA :
+  SubtargetFeature<"aggressive-fma",
+                   "HasAggressiveFMA",
+                   "true",
+                   "Enable Aggressive FMA for floating-point.">;
+
 //===----------------------------------------------------------------------===//
 // Architectures.
 //
@@ -390,6 +396,7 @@ def ProcSaphira  : SubtargetFeature<"saphira", "ARMProcFamily", "Saphira",
 def ProcThunderX2T99  : SubtargetFeature<"thunderx2t99", "ARMProcFamily",
                                          "ThunderX2T99",
                                          "Cavium ThunderX2 processors", [
+                                          FeatureAggressiveFMA,
                                           FeatureCRC,
                                           FeatureCrypto,
                                           FeatureFPARMv8,

lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -10982,6 +10982,10 @@ bool AArch64TargetLowering::isIntDivCheap(EVT VT, AttributeList Attr) const {
   return OptSize && !VT.isVector();
 }
 
+bool AArch64TargetLowering::enableAggressiveFMAFusion(EVT VT) const {
+  return Subtarget->hasAggressiveFMA() && VT.isFloatingPoint();
+}
+
 unsigned
 AArch64TargetLowering::getVaListSizeInBits(const DataLayout &DL) const {
   if (Subtarget->isTargetDarwin() || Subtarget->isTargetWindows())

lib/Target/AArch64/AArch64ISelLowering.h

@@ -456,6 +456,9 @@ public:
     return true;
   }
 
+  /// Enable aggressive FMA fusion on targets that want it.
+  bool enableAggressiveFMAFusion(EVT VT) const override;
+
   /// Returns the size of the platform's va_list object.
   unsigned getVaListSizeInBits(const DataLayout &DL) const override;
 

lib/Target/AArch64/AArch64Subtarget.h

@@ -80,6 +80,7 @@ protected:
   bool HasLSLFast = false;
   bool HasSVE = false;
   bool HasRCPC = false;
+  bool HasAggressiveFMA = false;
 
   // HasZeroCycleRegMove - Has zero-cycle register mov instructions.
   bool HasZeroCycleRegMove = false;
@@ -269,6 +270,7 @@ public:
   bool hasLSLFast() const { return HasLSLFast; }
   bool hasSVE() const { return HasSVE; }
   bool hasRCPC() const { return HasRCPC; }
+  bool hasAggressiveFMA() const { return HasAggressiveFMA; }
 
   bool isLittleEndian() const { return IsLittle; }