When a live virtual register is being clobbered by an implicit def, it is spilled

and the spill is its kill. However, if the local allocator has determined the
register has not been modified (possible when its value was reloaded), it would
not issue a restore. In that case, mark the last use of the virtual register as
kill.

llvm-svn: 46111

Author: Evan Cheng

llvm/lib/CodeGen/RegAllocLocal.cpp

@@ -86,6 +86,16 @@ namespace {
     //
     std::vector<unsigned> PhysRegsUseOrder;
 
+    // Virt2LastUseMap - This maps each virtual register to its last use
+    // (MachineInstr*, operand index pair).
+    IndexedMap<std::pair<MachineInstr*, unsigned>, VirtReg2IndexFunctor>
+    Virt2LastUseMap;
+
+    std::pair<MachineInstr*,unsigned>& getVirtRegLastUse(unsigned Reg) {
+      assert(MRegisterInfo::isVirtualRegister(Reg) && "Illegal VirtReg!");
+      return Virt2LastUseMap[Reg];
+    }
+
     // VirtRegModified - This bitset contains information about which virtual
     // registers need to be spilled back to memory when their registers are
     // scavenged.  If a virtual register has simply been rematerialized, there
@@ -282,8 +292,12 @@ void RALocal::spillVirtReg(MachineBasicBlock &MBB,
 
   const TargetInstrInfo* TII = MBB.getParent()->getTarget().getInstrInfo();
 
-  if (!isVirtRegModified(VirtReg))
+  if (!isVirtRegModified(VirtReg)) {
     DOUT << " which has not been modified, so no store necessary!";
+    std::pair<MachineInstr*, unsigned> &LastUse = getVirtRegLastUse(VirtReg);
+    if (LastUse.first)
+      LastUse.first->getOperand(LastUse.second).setIsKill();
+  }
 
   // Otherwise, there is a virtual register corresponding to this physical
   // register.  We only need to spill it into its stack slot if it has been
@@ -507,6 +521,7 @@ MachineInstr *RALocal::reloadVirtReg(MachineBasicBlock &MBB, MachineInstr *MI,
 
   MF->getRegInfo().setPhysRegUsed(PhysReg);
   MI->getOperand(OpNum).setReg(PhysReg);  // Assign the input register
+  getVirtRegLastUse(VirtReg) = std::make_pair(MI, OpNum);
   return MI;
 }
 
@@ -722,6 +737,7 @@ void RALocal::AllocateBasicBlock(MachineBasicBlock &MBB) {
           DestPhysReg = getReg(MBB, MI, DestVirtReg);
         MF->getRegInfo().setPhysRegUsed(DestPhysReg);
         markVirtRegModified(DestVirtReg);
+        getVirtRegLastUse(DestVirtReg) = std::make_pair((MachineInstr*)0, 0);
         MI->getOperand(i).setReg(DestPhysReg);  // Assign the output register
       }
     }
@@ -823,7 +839,8 @@ bool RALocal::runOnMachineFunction(MachineFunction &Fn) {
   // mapping for all virtual registers
   unsigned LastVirtReg = MF->getRegInfo().getLastVirtReg();
   Virt2PhysRegMap.grow(LastVirtReg);
-  VirtRegModified.resize(LastVirtReg-MRegisterInfo::FirstVirtualRegister);
+  Virt2LastUseMap.grow(LastVirtReg);
+  VirtRegModified.resize(LastVirtReg+1-MRegisterInfo::FirstVirtualRegister);
 
   // Loop over all of the basic blocks, eliminating virtual register references
   for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
@@ -834,6 +851,7 @@ bool RALocal::runOnMachineFunction(MachineFunction &Fn) {
   PhysRegsUsed.clear();
   VirtRegModified.clear();
   Virt2PhysRegMap.clear();
+  Virt2LastUseMap.clear();
   return true;
 }
 

llvm/test/CodeGen/X86/2008-01-16-FPStackifierAssert.ll

@@ -0,0 +1,35 @@
+; RUN: llvm-as < %s | llc -march=x86 -mattr=+sse2 -regalloc=local
+
+define void @SolveCubic(double %a, double %b, double %c, double %d, i32* %solutions, double* %x) {
+entry:
+	%tmp71 = load x86_fp80* null, align 16		; <x86_fp80> [#uses=1]
+	%tmp72 = fdiv x86_fp80 %tmp71, 0xKC000C000000000000000		; <x86_fp80> [#uses=1]
+	%tmp73 = add x86_fp80 0xK00000000000000000000, %tmp72		; <x86_fp80> [#uses=1]
+	%tmp7374 = fptrunc x86_fp80 %tmp73 to double		; <double> [#uses=1]
+	store double %tmp7374, double* null, align 8
+	%tmp81 = load double* null, align 8		; <double> [#uses=1]
+	%tmp82 = add double %tmp81, 0x401921FB54442D18		; <double> [#uses=1]
+	%tmp83 = fdiv double %tmp82, 3.000000e+00		; <double> [#uses=1]
+	%tmp84 = call double @cos( double %tmp83 )		; <double> [#uses=1]
+	%tmp85 = mul double 0.000000e+00, %tmp84		; <double> [#uses=1]
+	%tmp8586 = fpext double %tmp85 to x86_fp80		; <x86_fp80> [#uses=1]
+	%tmp87 = load x86_fp80* null, align 16		; <x86_fp80> [#uses=1]
+	%tmp88 = fdiv x86_fp80 %tmp87, 0xKC000C000000000000000		; <x86_fp80> [#uses=1]
+	%tmp89 = add x86_fp80 %tmp8586, %tmp88		; <x86_fp80> [#uses=1]
+	%tmp8990 = fptrunc x86_fp80 %tmp89 to double		; <double> [#uses=1]
+	store double %tmp8990, double* null, align 8
+	%tmp97 = load double* null, align 8		; <double> [#uses=1]
+	%tmp98 = add double %tmp97, 0x402921FB54442D18		; <double> [#uses=1]
+	%tmp99 = fdiv double %tmp98, 3.000000e+00		; <double> [#uses=1]
+	%tmp100 = call double @cos( double %tmp99 )		; <double> [#uses=1]
+	%tmp101 = mul double 0.000000e+00, %tmp100		; <double> [#uses=1]
+	%tmp101102 = fpext double %tmp101 to x86_fp80		; <x86_fp80> [#uses=1]
+	%tmp103 = load x86_fp80* null, align 16		; <x86_fp80> [#uses=1]
+	%tmp104 = fdiv x86_fp80 %tmp103, 0xKC000C000000000000000		; <x86_fp80> [#uses=1]
+	%tmp105 = add x86_fp80 %tmp101102, %tmp104		; <x86_fp80> [#uses=1]
+	%tmp105106 = fptrunc x86_fp80 %tmp105 to double		; <double> [#uses=1]
+	store double %tmp105106, double* null, align 8
+	ret void
+}
+
+declare double @cos(double)