[PATCH] [mips][FastISel] Clobber HI0/LO0 registers in MUL instructions.

[Vasileios Kalintiris]

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D9825

Files:
  llvm/trunk/lib/Target/Mips/MipsFastISel.cpp
  llvm/trunk/test/CodeGen/Mips/Fast-ISel/mul1.ll

Index: llvm/trunk/lib/Target/Mips/MipsFastISel.cpp
===================================================================
--- llvm/trunk/lib/Target/Mips/MipsFastISel.cpp
+++ llvm/trunk/lib/Target/Mips/MipsFastISel.cpp
@@ -156,6 +156,12 @@
                                    unsigned MemReg, int64_t MemOffset) {
     return emitInst(Opc, DstReg).addReg(MemReg).addImm(MemOffset);
   }
+
+  unsigned fastEmitInst_rr(unsigned MachineInstOpcode,
+                           const TargetRegisterClass *RC,
+                           unsigned Op0, bool Op0IsKill,
+                           unsigned Op1, bool Op1IsKill);
+
   // for some reason, this default is not generated by tablegen
   // so we explicitly generate it here.
   //
@@ -1563,6 +1569,33 @@
   }
 }
 
+unsigned MipsFastISel::fastEmitInst_rr(unsigned MachineInstOpcode,
+                                       const TargetRegisterClass *RC,
+                                       unsigned Op0, bool Op0IsKill,
+                                       unsigned Op1, bool Op1IsKill) {
+  // We treat the MUL instruction in a special way because it clobbers
+  // the HI0 & LO0 registers. The TableGen definition of this instruction can
+  // mark these registers only as implicitly defined. As a result, the
+  // register allocator runs out of registers when this instruction is
+  // followed by another instruction that defines the same registers too.
+  // We can fix this by explicitly marking those registers as dead.
+  if (MachineInstOpcode == Mips::MUL) {
+    unsigned ResultReg = createResultReg(RC);
+    const MCInstrDesc &II = TII.get(MachineInstOpcode);
+    Op0 = constrainOperandRegClass(II, Op0, II.getNumDefs());
+    Op1 = constrainOperandRegClass(II, Op1, II.getNumDefs() + 1);
+    BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, II, ResultReg)
+      .addReg(Op0, getKillRegState(Op0IsKill))
+      .addReg(Op1, getKillRegState(Op1IsKill))
+      .addReg(Mips::HI0, RegState::ImplicitDefine | RegState::Dead)
+      .addReg(Mips::LO0, RegState::ImplicitDefine | RegState::Dead);
+    return ResultReg;
+  }
+
+  return FastISel::fastEmitInst_rr(MachineInstOpcode, RC, Op0, Op0IsKill, Op1,
+                                   Op1IsKill);
+}
+
 namespace llvm {
 FastISel *Mips::createFastISel(FunctionLoweringInfo &funcInfo,
                                const TargetLibraryInfo *libInfo) {
Index: llvm/trunk/test/CodeGen/Mips/Fast-ISel/mul1.ll
===================================================================
--- llvm/trunk/test/CodeGen/Mips/Fast-ISel/mul1.ll
+++ llvm/trunk/test/CodeGen/Mips/Fast-ISel/mul1.ll
@@ -0,0 +1,18 @@
+; RUN: llc < %s -march=mipsel -mcpu=mips32 -O0 \
+; RUN:    -fast-isel -mips-fast-isel -relocation-model=pic
+; RUN: llc < %s -march=mipsel -mcpu=mips32r2 -O0 \
+; RUN:    -fast-isel -mips-fast-isel -relocation-model=pic
+
+; The test is just to make sure it is able to allocate
+; registers for this example. There was an issue with allocating AC0
+; after a mul instruction.
+
+declare { i32, i1 } @llvm.smul.with.overflow.i32(i32, i32)
+
+define i32 @foo(i32 %a, i32 %b)  {
+entry:
+  %0 = mul i32 %a, %b
+  %1 = call { i32, i1 } @llvm.smul.with.overflow.i32(i32 %0, i32 %b)
+  %2 = extractvalue { i32, i1 } %1, 0
+  ret i32 %2
+}

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