MachineRegisterInfo: Introduce isPhysRegUsed()

This method checks whether a physical regiser or any of its aliases are
used in the function.

Using this function in SIRegisterInfo::findUnusedReg() should also fix
this reported failure:

http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20150803/292143.html
http://reviews.llvm.org/rL242173#inline-533

The report doesn't come with a testcase and I don't know enough about
AMDGPU to create one myself.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245329 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineRegisterInfo.h

@@ -644,9 +644,16 @@ public:
   /// Return true if the specified register is modified in this function.
   /// This checks that no defining machine operands exist for the register or
   /// any of its aliases. Definitions found on functions marked noreturn are
-  /// ignored.
+  /// ignored. The register is also considered modified when it is set in the
+  /// UsedPhysRegMask.
   bool isPhysRegModified(unsigned PhysReg) const;
 
+  /// Return true if the specified register is modified or read in this
+  /// function. This checks that no machine operands exist for the register or
+  /// any of its aliases. The register is also considered used when it is set
+  /// in the UsedPhysRegMask.
+  bool isPhysRegUsed(unsigned PhysReg) const;
+
   /// addPhysRegsUsedFromRegMask - Mark any registers not in RegMask as used.
   /// This corresponds to the bit mask attached to register mask operands.
   void addPhysRegsUsedFromRegMask(const uint32_t *RegMask) {

lib/CodeGen/ExecutionDepsFix.cpp

@@ -733,13 +733,12 @@ bool ExeDepsFix::runOnMachineFunction(MachineFunction &mf) {
   // completely.
   bool anyregs = false;
   const MachineRegisterInfo &MRI = mf.getRegInfo();
-  for (TargetRegisterClass::const_iterator I = RC->begin(), E = RC->end();
+  for (unsigned Reg : *RC) {
-       I != E && !anyregs; ++I)
+    if (MRI.isPhysRegUsed(Reg)) {
-    for (MCRegAliasIterator AI(*I, TRI, true); AI.isValid(); ++AI)
-      if (!MRI.reg_nodbg_empty(*AI)) {
       anyregs = true;
       break;
     }
+  }
   if (!anyregs) return false;
 
   // Initialize the AliasMap on the first use.

lib/CodeGen/MachineRegisterInfo.cpp

@@ -489,3 +489,15 @@ bool MachineRegisterInfo::isPhysRegModified(unsigned PhysReg) const {
   }
   return false;
 }
+
+bool MachineRegisterInfo::isPhysRegUsed(unsigned PhysReg) const {
+  if (UsedPhysRegMask.test(PhysReg))
+    return true;
+  const TargetRegisterInfo *TRI = getTargetRegisterInfo();
+  for (MCRegAliasIterator AliasReg(PhysReg, TRI, true); AliasReg.isValid();
+       ++AliasReg) {
+    if (!reg_nodbg_empty(*AliasReg))
+      return true;
+  }
+  return false;
+}

lib/Target/AMDGPU/SIRegisterInfo.cpp

@@ -495,12 +495,9 @@ unsigned SIRegisterInfo::getPreloadedValue(const MachineFunction &MF,
 //         AMDGPU::NoRegister.
 unsigned SIRegisterInfo::findUnusedRegister(const MachineRegisterInfo &MRI,
                                            const TargetRegisterClass *RC) const {
-
+  for (unsigned Reg : *RC)
-  for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end();
+    if (!MRI.isPhysRegUsed(Reg))
-       I != E; ++I) {
+      return Reg;
-    if (MRI.reg_nodbg_empty(*I))
-      return *I;
-  }
   return AMDGPU::NoRegister;
 }