[llvm] 310f839 - DAG: Lower is.fpclass fcInf to fcmp of fabs

[Matt Arsenault via llvm-commits]

Author: Matt Arsenault
Date: 2023-07-07T17:00:10-04:00
New Revision: 310f83961269a574d753932dc5f0c8fd44027781

URL: https://github.com/llvm/llvm-project/commit/310f83961269a574d753932dc5f0c8fd44027781
DIFF: https://github.com/llvm/llvm-project/commit/310f83961269a574d753932dc5f0c8fd44027781.diff

LOG: DAG: Lower is.fpclass fcInf to fcmp of fabs

InstCombine should have taken care of this, but I think
this is more useful in the future when the expansion
tries to handle multiple cases at a time with fcmp.

x87 looks worse to me but the only thing I know about it is that
I aggressively do not care about it.

https://reviews.llvm.org/D143198

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
    llvm/test/CodeGen/PowerPC/is_fpclass.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index e1296e69447944..41680061ff1f0e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -8125,6 +8125,18 @@ SDValue TargetLowering::expandIS_FPCLASS(EVT ResultVT, SDValue Op,
       return DAG.getSetCC(DL, ResultVT, Op, Op,
                           IsInverted ? ISD::SETO : ISD::SETUO);
     }
+
+    if (Test == fcInf &&
+        isCondCodeLegalOrCustom(IsInverted ? ISD::SETUNE : ISD::SETOEQ,
+                                OperandVT.getScalarType().getSimpleVT()) &&
+        isOperationLegalOrCustom(ISD::FABS, OperandVT.getScalarType())) {
+      // isinf(x) --> fabs(x) == inf
+      SDValue Abs = DAG.getNode(ISD::FABS, DL, OperandVT, Op);
+      SDValue Inf =
+          DAG.getConstantFP(APFloat::getInf(Semantics), DL, OperandVT);
+      return DAG.getSetCC(DL, ResultVT, Abs, Inf,
+                          IsInverted ? ISD::SETUNE : ISD::SETOEQ);
+    }
   }
 
   // In the general case use integer operations.

diff  --git a/llvm/test/CodeGen/PowerPC/is_fpclass.ll b/llvm/test/CodeGen/PowerPC/is_fpclass.ll
index a4368a1dca26e3..baf69dd787b250 100644
--- a/llvm/test/CodeGen/PowerPC/is_fpclass.ll
+++ b/llvm/test/CodeGen/PowerPC/is_fpclass.ll
@@ -117,13 +117,12 @@ define i1 @isinf_float(float %x) nounwind {
 define i1 @isinf_ppc_fp128(ppc_fp128 %x) nounwind {
 ; CHECK-LABEL: isinf_ppc_fp128:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    mffprd 3, 1
-; CHECK-NEXT:    li 4, 2047
-; CHECK-NEXT:    clrldi 3, 3, 1
-; CHECK-NEXT:    rldic 4, 4, 52, 1
-; CHECK-NEXT:    cmpd 3, 4
-; CHECK-NEXT:    li 3, 0
+; CHECK-NEXT:    addis 3, 2, .LCPI9_0 at toc@ha
+; CHECK-NEXT:    xsabsdp 0, 1
 ; CHECK-NEXT:    li 4, 1
+; CHECK-NEXT:    lfs 1, .LCPI9_0 at toc@l(3)
+; CHECK-NEXT:    li 3, 0
+; CHECK-NEXT:    fcmpu 0, 0, 1
 ; CHECK-NEXT:    iseleq 3, 4, 3
 ; CHECK-NEXT:    blr
   %1 = call i1 @llvm.is.fpclass.ppcf128(ppc_fp128 %x, i32 516)  ; 0x204 = "inf"