Optionally enable more-aggressive FMA formation in DAGCombine
The heuristic used by DAGCombine to form FMAs checks that the FMUL has only one
use, but this is overly-conservative on some systems. Specifically, if the FMA
and the FADD have the same latency (and the FMA does not compete for resources
with the FMUL any more than the FADD does), there is no need for the
restriction, and furthermore, forming the FMA leaving the FMUL can still allow
for higher overall throughput and decreased critical-path length.
Here we add a new TLI callback, enableAggressiveFMAFusion, false by default, to
elide the hasOneUse check. This is enabled for PowerPC by default, as most
PowerPC systems will benefit.
Patch by Olivier Sallenave, thanks!
llvm-svn: 218120
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 6eded03..fd188fe 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -826,6 +826,11 @@
return VT.changeVectorElementTypeToInteger();
}
+bool PPCTargetLowering::enableAggressiveFMAFusion(EVT VT) const {
+ assert(VT.isFloatingPoint() && "Non-floating-point FMA?");
+ return true;
+}
+
//===----------------------------------------------------------------------===//
// Node matching predicates, for use by the tblgen matching code.
//===----------------------------------------------------------------------===//
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index de8f836..c53dc83 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -360,6 +360,11 @@
/// getSetCCResultType - Return the ISD::SETCC ValueType
EVT getSetCCResultType(LLVMContext &Context, EVT VT) const override;
+ /// Return true if target always beneficiates from combining into FMA for a
+ /// given value type. This must typically return false on targets where FMA
+ /// takes more cycles to execute than FADD.
+ bool enableAggressiveFMAFusion(EVT VT) const override;
+
/// getPreIndexedAddressParts - returns true by value, base pointer and
/// offset pointer and addressing mode by reference if the node's address
/// can be legally represented as pre-indexed load / store address.