Propagate fmf for setcc/select folds

[mcberg2017]

Summary

This change facilitates propagating fmf which was placed on setcc from fcmp through folds with selects so that back ends can model this path for arithmetic folds on selects in SDAG.

[qcolombet]

LGTM.

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

7878 ↗

(On Diff #201775)

Nit: Period at the end of sentences.

llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

if (!LegalOperations && TLI.isOperationLegalOrCustom(ISD::UADDO, VT) &&
         //   %r = select %u1, -1, %u0
         SDVTList VTs = DAG.getVTList(VT, VT0);
         SDValue UAO = DAG.getNode(ISD::UADDO, DL, VTs, Cond0, N2.getOperand(1));
         return DAG.getSelect(DL, VT, UAO.getValue(1), N1, UAO.getValue(0));
       }
     }
 
     if (TLI.isOperationLegal(ISD::SELECT_CC, VT) ||
-        (!LegalOperations && TLI.isOperationLegalOrCustom(ISD::SELECT_CC, VT)))
-      return DAG.getNode(ISD::SELECT_CC, DL, VT, Cond0, Cond1, N1, N2,
-                         N0.getOperand(2));
+        (!LegalOperations &&
+         TLI.isOperationLegalOrCustom(ISD::SELECT_CC, VT))) {
+      // Any flags available in a select/setcc fold will be on the setcc as they
+      // migrated from fcmp
+      const SDNodeFlags Flags = N0.getNode()->getFlags();
+      SDValue SelectNode = DAG.getNode(ISD::SELECT_CC, DL, VT, Cond0, Cond1, N1,
+                                       N2, N0.getOperand(2));
+      SelectNode->setFlags(Flags);
+      return SelectNode;
+    }
 
     return SimplifySelect(DL, N0, N1, N2);
   }
 
   return SDValue();
 }
 
 static

llvm/trunk/test/CodeGen/PowerPC/fmf-propagation.ll

 ; GLOBAL-NEXT:    blr
   %rt = call fast float @llvm.sqrt.f32(float %x)
   ret float %rt
 }
 
 ; fcmp can have fast-math-flags.
 
 ; FMFDEBUG-LABEL: Optimized lowered selection DAG: %bb.0 'fcmp_nnan:'
-; FMFDEBUG:         select_cc {{t[0-9]+}}
+; FMFDEBUG:         select_cc nnan {{t[0-9]+}}
 ; FMFDEBUG:       Type-legalized selection DAG: %bb.0 'fcmp_nnan:'
 
 ; GLOBALDEBUG-LABEL: Optimized lowered selection DAG: %bb.0 'fcmp_nnan:'
-; GLOBALDEBUG:         select_cc {{t[0-9]+}}
+; GLOBALDEBUG:         select_cc nnan {{t[0-9]+}}
 ; GLOBALDEBUG:       Type-legalized selection DAG: %bb.0 'fcmp_nnan:'
 
 define double @fcmp_nnan(double %a, double %y, double %z) {
 ; FMF-LABEL: fcmp_nnan:
 ; FMF:       # %bb.0:
 ; FMF-NEXT:    xxlxor 0, 0, 0
 ; FMF-NEXT:    xscmpudp 0, 1, 0
 ; FMF-NEXT:    blt 0, .LBB12_2