[PATCH] D27573: [X86] Fix bug in r288804.

[Ayman Musa via Phabricator via llvm-commits]

aymanmus created this revision.
aymanmus added reviewers: mkuper, RKSimon, spatel, zvi.
aymanmus added a subscriber: llvm-commits.

When creating the load from constant pool, check if there was already a load to the same constant, and abort if found.
The additional use of the load will prevent the pattern from memory folding the broadcast.


https://reviews.llvm.org/D27573

Files:
  lib/Target/X86/X86ISelLowering.cpp


Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -6394,6 +6394,7 @@
       const TargetLowering &TLI = DAG.getTargetLoweringInfo();
       LLVMContext *Ctx = DAG.getContext();
       MVT PVT = TLI.getPointerTy(DAG.getDataLayout());
+      SDValue Brdcst;
       if (Subtarget.hasAVX()) {
         if (SplatBitSize <= 64 && Subtarget.hasAVX2() &&
             !(SplatBitSize == 64 && Subtarget.is32Bit())) {
@@ -6410,9 +6411,8 @@
               CVT, dl, DAG.getEntryNode(), CP,
               MachinePointerInfo::getConstantPool(DAG.getMachineFunction()),
               Alignment);
-          SDValue Brdcst = DAG.getNode(X86ISD::VBROADCAST, dl,
+          Brdcst = DAG.getNode(X86ISD::VBROADCAST, dl,
                                        MVT::getVectorVT(CVT, Repeat), Ld);
-          return DAG.getBitcast(VT, Brdcst);
         } else if (SplatBitSize == 32 || SplatBitSize == 64) {
           // Splatted value can fit in one FLOAT constant in constant pool.
           // Load the constant and broadcast it.
@@ -6432,9 +6432,8 @@
               CVT, dl, DAG.getEntryNode(), CP,
               MachinePointerInfo::getConstantPool(DAG.getMachineFunction()),
               Alignment);
-          SDValue Brdcst = DAG.getNode(X86ISD::VBROADCAST, dl,
+          Brdcst = DAG.getNode(X86ISD::VBROADCAST, dl,
                                        MVT::getVectorVT(CVT, Repeat), Ld);
-          return DAG.getBitcast(VT, Brdcst);
         } else if (SplatBitSize > 64) {
           // Load the vector of constants and broadcast it.
           MVT CVT = VT.getScalarType();
@@ -6447,9 +6446,15 @@
               MVT::getVectorVT(CVT, NumElm), dl, DAG.getEntryNode(), VCP,
               MachinePointerInfo::getConstantPool(DAG.getMachineFunction()),
               Alignment);
-          SDValue Brdcst = DAG.getNode(X86ISD::SUBV_BROADCAST, dl, VT, Ld);
-          return DAG.getBitcast(VT, Brdcst);
+          Brdcst = DAG.getNode(X86ISD::SUBV_BROADCAST, dl, VT, Ld);
+        } else {
+          return SDValue();
         }
+        // If the load already had a use, we can't fold it into the broadcast.
+        // So fallback to the original state.
+        if (!Ld.hasOneUse())
+          return SDValue();
+        return DAG.getBitcast(VT, Brdcst);
       }
     }
     return SDValue();


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