From 4494d69862451827cf0a64a101c279728626fb84 Mon Sep 17 00:00:00 2001
From: Tim Northover <tnorthover@apple.com>
Date: Tue, 18 Oct 2016 19:47:57 +0000
Subject: [PATCH] GlobalISel: support floating-point constants on AArch64.

Patch from Ahmed Bougacha.

llvm-svn: 284523
---
 .../Target/AArch64/AArch64InstructionSelector.cpp  | 81 ++++++++++++++++++++--
 .../AArch64/GlobalISel/arm64-instructionselect.mir | 35 ++++++++++
 2 files changed, 109 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
index 1f2be90..ebfd78b 100644
--- a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
@@ -513,14 +513,81 @@ bool AArch64InstructionSelector::select(MachineInstr &I) const {
     return constrainSelectedInstRegOperands(*MIB.getInstr(), TII, TRI, RBI);
   }
 
+  case TargetOpcode::G_FCONSTANT:
   case TargetOpcode::G_CONSTANT: {
-    if (Ty.getSizeInBits() <= 32)
-      I.setDesc(TII.get(AArch64::MOVi32imm));
-    else if (Ty.getSizeInBits() <= 64)
-      I.setDesc(TII.get(AArch64::MOVi64imm));
-    else
-      return false;
-    return constrainSelectedInstRegOperands(I, TII, TRI, RBI);
+    const bool isFP = Opcode == TargetOpcode::G_FCONSTANT;
+
+    const LLT s32 = LLT::scalar(32);
+    const LLT s64 = LLT::scalar(64);
+    const LLT p0 = LLT::pointer(0, 64);
+
+    const unsigned DefReg = I.getOperand(0).getReg();
+    const LLT DefTy = MRI.getType(DefReg);
+    const unsigned DefSize = DefTy.getSizeInBits();
+    const RegisterBank &RB = *RBI.getRegBank(DefReg, MRI, TRI);
+
+    // FIXME: Redundant check, but even less readable when factored out.
+    if (isFP) {
+      if (Ty != s32 && Ty != s64) {
+        DEBUG(dbgs() << "Unable to materialize FP " << Ty
+                     << " constant, expected: " << s32 << " or " << s64
+                     << '\n');
+        return false;
+      }
+
+      if (RB.getID() != AArch64::FPRRegBankID) {
+        DEBUG(dbgs() << "Unable to materialize FP " << Ty
+                     << " constant on bank: " << RB << ", expected: FPR\n");
+        return false;
+      }
+    } else {
+      if (Ty != s32 && Ty != s64 && Ty != p0) {
+        DEBUG(dbgs() << "Unable to materialize integer " << Ty
+                     << " constant, expected: " << s32 << ", " << s64 << ", or "
+                     << p0 << '\n');
+        return false;
+      }
+
+      if (RB.getID() != AArch64::GPRRegBankID) {
+        DEBUG(dbgs() << "Unable to materialize integer " << Ty
+                     << " constant on bank: " << RB << ", expected: GPR\n");
+        return false;
+      }
+    }
+
+    const unsigned MovOpc =
+        DefSize == 32 ? AArch64::MOVi32imm : AArch64::MOVi64imm;
+
+    I.setDesc(TII.get(MovOpc));
+
+    if (isFP) {
+      const TargetRegisterClass &GPRRC =
+          DefSize == 32 ? AArch64::GPR32RegClass : AArch64::GPR64RegClass;
+      const TargetRegisterClass &FPRRC =
+          DefSize == 32 ? AArch64::FPR32RegClass : AArch64::FPR64RegClass;
+
+      const unsigned DefGPRReg = MRI.createVirtualRegister(&GPRRC);
+      MachineOperand &RegOp = I.getOperand(0);
+      RegOp.setReg(DefGPRReg);
+
+      BuildMI(MBB, std::next(I.getIterator()), I.getDebugLoc(),
+              TII.get(AArch64::COPY))
+          .addDef(DefReg)
+          .addUse(DefGPRReg);
+
+      if (!RBI.constrainGenericRegister(DefReg, FPRRC, MRI)) {
+        DEBUG(dbgs() << "Failed to constrain G_FCONSTANT def operand\n");
+        return false;
+      }
+
+      MachineOperand &ImmOp = I.getOperand(1);
+      // FIXME: Is going through int64_t always correct?
+      ImmOp.ChangeToImmediate(
+          ImmOp.getFPImm()->getValueAPF().bitcastToAPInt().getZExtValue());
+    }
+
+    constrainSelectedInstRegOperands(I, TII, TRI, RBI);
+    return true;
   }
 
   case TargetOpcode::G_FRAME_INDEX: {
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-instructionselect.mir b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-instructionselect.mir
index 2d34dfe..6ea29f0 100644
--- a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-instructionselect.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-instructionselect.mir
@@ -103,6 +103,9 @@
   define i32 @const_s32() { ret i32 42 }
   define i64 @const_s64() { ret i64 1234567890123 }
 
+  define i32 @fconst_s32() { ret i32 42 }
+  define i64 @fconst_s64() { ret i64 1234567890123 }
+
   define i8* @gep(i8* %in) { ret i8* undef }
 
   @var_local = global i8 0
@@ -1879,6 +1882,38 @@ body:             |
 ...
 
 ---
+# CHECK-LABEL: name: fconst_s32
+name:            fconst_s32
+legalized:       true
+regBankSelected: true
+registers:
+  - { id: 0, class: fpr }
+
+# CHECK:  body:
+# CHECK: [[TMP:%[0-9]+]] = MOVi32imm 1080033280
+# CHECK: %0 = COPY [[TMP]]
+body:             |
+  bb.0:
+    %0(s32) = G_FCONSTANT float 3.5
+...
+
+---
+# CHECK-LABEL: name: fconst_s64
+name:            fconst_s64
+legalized:       true
+regBankSelected: true
+registers:
+  - { id: 0, class: fpr }
+
+# CHECK:  body:
+# CHECK: [[TMP:%[0-9]+]] = MOVi64imm 4607182418800017408
+# CHECK: %0 = COPY [[TMP]]
+body:             |
+  bb.0:
+    %0(s64) = G_FCONSTANT double 1.0
+...
+
+---
 # CHECK-LABEL: name: gep
 name:            gep
 legalized:       true
-- 
2.7.4