[PATCH] D17294: Fix for PR 26500

[Kit Barton via llvm-commits]

kbarton added inline comments.

================
Comment at: lib/Target/PowerPC/PPCFrameLowering.cpp:621
@@ +620,3 @@
+    int FirstScratchReg = BV.find_first();
+    *SR1 = FirstScratchReg == -1 ? (unsigned)PPC::NoRegister : FirstScratchReg;
+  }
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I don't think we can use PPC::NoRegister here - it breaks the contract of the function.
Read the comments in the function carefully - it cleary states what is expected if all registers are not available. We return false and return the default registers (R0 and R12). 

I think it's a much better idea to always check the return code, and assert in cases where it is expected to return true. That is, when we are asking whether there are registers available, the return value is used to make a decision (i.e., in canUseAsPrologue). Once the decision is made, we use the same function to get the actual registers available (i.e., emitPrologue). In that case, this function should always return true, or something went wrong.


Repository:
  rL LLVM

http://reviews.llvm.org/D17294