Fixing bug committed in rev. 278321

[myatsina]

Summary

In theory the indices of RC (and thus the index used for LiveRegs) may differ from the indices of OpRC.
Fixed the code to extract the correct RC index.
OpRC contains the first X consecutive elements of RC, and thus their indices are currently de facto the same, therefore a test cannot be added at this point.

[mkuper]

lib/CodeGen/ExecutionDepsFix.cpp

512

If the only thing you use rx for is OpRC->getRegister(), can you just iterate over OpRC directly? This will make it less confusing.
I see TargetRegisterClass has a begin()/end(), but I don't see a method that returns a range - perhaps it's worth adding as well, so you can use a range for here.

[myatsina]

Added use of range iterator over registers in the RegisterClass

[mkuper]

LGTM with a small nit about the naming.

include/llvm/Target/TargetRegisterInfo.h

92 ↗

(On Diff #68156)

For iterator_ranges, we tend to use names that follow the STL convention, not LLVM. So I'd suggest something like "registers()" or "regs()".

[MatzeB]

llvm/trunk/include/llvm/Target/TargetRegisterInfo.h

91–94 ↗

(On Diff #68334)

Why did you add this?

for (unsigned Reg : RegClass) { } already worked!

lib/CodeGen/ExecutionDepsFix.cpp

for (MachineOperand &CurrMO : MI->operands()) {
     MO.setReg(CurrMO.getReg());
     return;
   }
 
   // Go over all registers in the register class and find the register with
   // max clearance or clearance higher than Pref.
   unsigned MaxClearance = 0;
   unsigned MaxClearanceReg = OriginalReg;
   for (unsigned rx = 0; rx < OpRC->getNumRegs(); ++rx) {
-    unsigned Clearance = CurInstr - LiveRegs[rx].Def;
+    unsigned Reg = OpRC->getRegister(rx);
+    assert(AliasMap[Reg].size() == 1 &&
+           "Reg is expected to be mapped to a single index");
+    int RCrx = *regIndices(Reg).begin();
+    unsigned Clearance = CurInstr - LiveRegs[RCrx].Def;
     if (Clearance <= MaxClearance)
       continue;
     MaxClearance = Clearance;
-    MaxClearanceReg = OpRC->getRegister(rx);
+    MaxClearanceReg = Reg;
 
     if (MaxClearance > Pref)
       break;
   }
 
   // Update the operand if we found a register with better clearance.
   if (MaxClearanceReg != OriginalReg)
     MO.setReg(MaxClearanceReg);