[PATCH] D81893: [AArch64][GlobalISel] Emit constant pool loads for 64 bit fp immediates.

[Amara Emerson via Phabricator via llvm-commits]

aemerson created this revision.
aemerson added a reviewer: paquette.
aemerson added a project: LLVM.
Herald added subscribers: danielkiss, hiraditya, kristof.beyls, rovka.

Note: don't don this for integer 64 bit materialization to match SDAG.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D81893

Files:
  llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/select-imm.mir


Index: llvm/test/CodeGen/AArch64/GlobalISel/select-imm.mir
===================================================================
--- llvm/test/CodeGen/AArch64/GlobalISel/select-imm.mir
+++ llvm/test/CodeGen/AArch64/GlobalISel/select-imm.mir
@@ -6,6 +6,7 @@
 
   define void @imm_s32_gpr() { ret void }
   define void @imm_s64_gpr() { ret void }
+  define void @test_f64_cp() { ret void }
 
 ...
 
@@ -49,3 +50,29 @@
     %0(s64) = G_CONSTANT i64 1234
     $x0 = COPY %0(s64)
 ...
+
+# 64b FP immediates need to be loaded.
+---
+name:            test_f64_cp
+legalized:       true
+regBankSelected: true
+liveins:
+  - { reg: '$d0' }
+body:             |
+  bb.1 (%ir-block.0):
+    liveins: $d0
+
+    ; CHECK-LABEL: name: test_f64_cp
+    ; CHECK: [[COPY:%[0-9]+]]:fpr64 = COPY $d0
+    ; CHECK: [[ADRP:%[0-9]+]]:gpr64common = ADRP target-flags(aarch64-page) %const.0
+    ; CHECK: [[LDRDui:%[0-9]+]]:fpr64 = LDRDui [[ADRP]], target-flags(aarch64-pageoff, aarch64-nc) %const.0
+    ; CHECK: [[FADDDrr:%[0-9]+]]:fpr64 = FADDDrr [[COPY]], [[LDRDui]]
+    ; CHECK: $d0 = COPY [[FADDDrr]]
+    ; CHECK: RET_ReallyLR implicit $d0
+    %0:fpr(s64) = COPY $d0
+    %1:fpr(s64) = G_FCONSTANT double 0x3FEFF7CED916872B
+    %2:fpr(s64) = G_FADD %0, %1
+    $d0 = COPY %2(s64)
+    RET_ReallyLR implicit $d0
+
+...
Index: llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
===================================================================
--- llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
+++ llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
@@ -144,8 +144,9 @@
   bool selectBrJT(MachineInstr &I, MachineRegisterInfo &MRI) const;
   bool selectTLSGlobalValue(MachineInstr &I, MachineRegisterInfo &MRI) const;
 
-  unsigned emitConstantPoolEntry(Constant *CPVal, MachineFunction &MF) const;
-  MachineInstr *emitLoadFromConstantPool(Constant *CPVal,
+  unsigned emitConstantPoolEntry(const Constant *CPVal,
+                                 MachineFunction &MF) const;
+  MachineInstr *emitLoadFromConstantPool(const Constant *CPVal,
                                          MachineIRBuilder &MIRBuilder) const;
 
   // Emit a vector concat operation.
@@ -2046,6 +2047,21 @@
       if (emitFMovForFConstant(I, MRI))
         return true;
 
+      // For 64b values, emit a constant pool load instead.
+      if (DefSize == 64) {
+        auto *FPImm = I.getOperand(1).getFPImm();
+        MachineIRBuilder MIB(I);
+        auto *LoadMI =
+            AArch64InstructionSelector::emitLoadFromConstantPool(FPImm, MIB);
+        if (!LoadMI) {
+          LLVM_DEBUG(dbgs() << "Failed to load double constant pool entry\n");
+          return false;
+        }
+        MIB.buildCopy({DefReg}, {LoadMI->getOperand(0).getReg()});
+        I.eraseFromParent();
+        return RBI.constrainGenericRegister(DefReg, FPRRC, MRI);
+      }
+
       // Nope. Emit a copy and use a normal mov instead.
       const Register DefGPRReg = MRI.createVirtualRegister(&GPRRC);
       MachineOperand &RegOp = I.getOperand(0);
@@ -3572,7 +3588,7 @@
 }
 
 unsigned
-AArch64InstructionSelector::emitConstantPoolEntry(Constant *CPVal,
+AArch64InstructionSelector::emitConstantPoolEntry(const Constant *CPVal,
                                                   MachineFunction &MF) const {
   Type *CPTy = CPVal->getType();
   Align Alignment = MF.getDataLayout().getPrefTypeAlign(CPTy);
@@ -3582,7 +3598,7 @@
 }
 
 MachineInstr *AArch64InstructionSelector::emitLoadFromConstantPool(
-    Constant *CPVal, MachineIRBuilder &MIRBuilder) const {
+    const Constant *CPVal, MachineIRBuilder &MIRBuilder) const {
   unsigned CPIdx = emitConstantPoolEntry(CPVal, MIRBuilder.getMF());
 
   auto Adrp =


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