[PATCH] D72312: [DAGCombine] Fold the (fma -x, y, -z) to -(fma x, y, z)

[qshanz via Phabricator via llvm-commits]

steven.zhang created this revision.
steven.zhang added reviewers: efriedma, craig.topper, RKSimon, dmgreen, arsenm, jsji, nemanjai, PowerPC.
Herald added subscribers: wuzish, hiraditya, wdng.
Herald added a project: LLVM.

This is a positive combination as long as the NEG is NOT free, as we are reducing the number of NEG from two to one.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72312

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/PowerPC/fma-combine.ll


Index: llvm/test/CodeGen/PowerPC/fma-combine.ll
===================================================================
--- llvm/test/CodeGen/PowerPC/fma-combine.ll
+++ llvm/test/CodeGen/PowerPC/fma-combine.ll
@@ -6,14 +6,12 @@
 define double @fma_combine1(double %a, double %b, double %c) {
 ; CHECK-FAST-LABEL: fma_combine1:
 ; CHECK-FAST:       # %bb.0: # %entry
-; CHECK-FAST-NEXT:    xsnegdp 0, 3
-; CHECK-FAST-NEXT:    xsmsubadp 1, 0, 2
+; CHECK-FAST-NEXT:    xsnmaddadp 1, 3, 2
 ; CHECK-FAST-NEXT:    blr
 ;
 ; CHECK-FAST-NOVSX-LABEL: fma_combine1:
 ; CHECK-FAST-NOVSX:       # %bb.0: # %entry
-; CHECK-FAST-NOVSX-NEXT:    fneg 0, 3
-; CHECK-FAST-NOVSX-NEXT:    fmsub 1, 0, 2, 1
+; CHECK-FAST-NOVSX-NEXT:    fnmadd 1, 3, 2, 1
 ; CHECK-FAST-NOVSX-NEXT:    blr
 ;
 ; CHECK-LABEL: fma_combine1:
@@ -32,14 +30,12 @@
 define double @fma_combine2(double %a, double %b, double %c) {
 ; CHECK-FAST-LABEL: fma_combine2:
 ; CHECK-FAST:       # %bb.0: # %entry
-; CHECK-FAST-NEXT:    xsnegdp 0, 3
-; CHECK-FAST-NEXT:    xsmsubadp 1, 2, 0
+; CHECK-FAST-NEXT:    xsnmaddadp 1, 2, 3
 ; CHECK-FAST-NEXT:    blr
 ;
 ; CHECK-FAST-NOVSX-LABEL: fma_combine2:
 ; CHECK-FAST-NOVSX:       # %bb.0: # %entry
-; CHECK-FAST-NOVSX-NEXT:    fneg 0, 3
-; CHECK-FAST-NOVSX-NEXT:    fmsub 1, 2, 0, 1
+; CHECK-FAST-NOVSX-NEXT:    fnmadd 1, 2, 3, 1
 ; CHECK-FAST-NOVSX-NEXT:    blr
 ;
 ; CHECK-LABEL: fma_combine2:
@@ -106,19 +102,17 @@
 define double @fma_combine_one_use(double %a, double %b, double %c) {
 ; CHECK-FAST-LABEL: fma_combine_one_use:
 ; CHECK-FAST:       # %bb.0: # %entry
-; CHECK-FAST-NEXT:    xsnegdp 0, 3
+; CHECK-FAST-NEXT:    xsnegdp 0, 1
 ; CHECK-FAST-NEXT:    addis 3, 2, v at toc@ha
-; CHECK-FAST-NEXT:    xsnegdp 3, 1
-; CHECK-FAST-NEXT:    xsmsubadp 1, 0, 2
-; CHECK-FAST-NEXT:    stfd 3, v at toc@l(3)
+; CHECK-FAST-NEXT:    xsnmaddadp 1, 3, 2
+; CHECK-FAST-NEXT:    stfd 0, v at toc@l(3)
 ; CHECK-FAST-NEXT:    blr
 ;
 ; CHECK-FAST-NOVSX-LABEL: fma_combine_one_use:
 ; CHECK-FAST-NOVSX:       # %bb.0: # %entry
-; CHECK-FAST-NOVSX-NEXT:    fneg 0, 3
-; CHECK-FAST-NOVSX-NEXT:    addis 3, 2, v at toc@ha
-; CHECK-FAST-NOVSX-NEXT:    fmsub 0, 0, 2, 1
+; CHECK-FAST-NOVSX-NEXT:    fnmadd 0, 3, 2, 1
 ; CHECK-FAST-NOVSX-NEXT:    fneg 2, 1
+; CHECK-FAST-NOVSX-NEXT:    addis 3, 2, v at toc@ha
 ; CHECK-FAST-NOVSX-NEXT:    fmr 1, 0
 ; CHECK-FAST-NOVSX-NEXT:    stfd 2, v at toc@l(3)
 ; CHECK-FAST-NOVSX-NEXT:    blr
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -12637,6 +12637,20 @@
                                      DAG.getConstantFP(-1.0, DL, VT), Flags),
                          Flags);
     }
+
+    if (N2.getOpcode() == ISD::FNEG && !TLI.isFNegFree(VT)) {
+      // (fma (fneg x), y, (fneg z)) -> fneg (fma x, y, z)
+      if (N0.getOpcode() == ISD::FNEG && (N2.hasOneUse() || N0.hasOneUse()))
+        return DAG.getNode(ISD::FNEG, DL, VT,
+                           DAG.getNode(ISD::FMA, DL, VT, N0.getOperand(0), N1,
+                                       N2.getOperand(0), Flags), Flags);
+
+      // (fma x, (fneg y), (fneg z)) -> fneg (fma x, y, z)
+      if (N1.getOpcode() == ISD::FNEG && (N2.hasOneUse() || N1.hasOneUse()))
+        return DAG.getNode(ISD::FNEG, DL, VT,
+                           DAG.getNode(ISD::FMA, DL, VT, N0, N1.getOperand(0),
+                                       N2.getOperand(0), Flags), Flags);
+    }
   }
 
   return SDValue();


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D72312.236496.patch
Type: text/x-patch
Size: 3538 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200107/902c37d5/attachment.bin>