[PATCH] D32999: [UnreachableBlockElim] Check return value of constrainRegClass().

[Mikael Holmén via Phabricator via llvm-commits]

uabelho created this revision.

MachineRegisterInfo::constrainRegClass() can fail if two register classes
don't have a common subclass or if the register class doesn't contain
enough registers. Check the return value before trying to remove Phi nodes,
and if we can't constrain, we output a COPY instead of simply replacing
registers.


https://reviews.llvm.org/D32999

Files:
  lib/CodeGen/UnreachableBlockElim.cpp


Index: lib/CodeGen/UnreachableBlockElim.cpp
===================================================================
--- lib/CodeGen/UnreachableBlockElim.cpp
+++ lib/CodeGen/UnreachableBlockElim.cpp
@@ -206,8 +206,8 @@
         if (InputReg != OutputReg) {
           MachineRegisterInfo &MRI = F.getRegInfo();
           unsigned InputSub = Input.getSubReg();
-          if (InputSub == 0) {
-            MRI.constrainRegClass(InputReg, MRI.getRegClass(OutputReg));
+          if (InputSub == 0 &&
+              MRI.constrainRegClass(InputReg, MRI.getRegClass(OutputReg))) {
             MRI.replaceRegWith(OutputReg, InputReg);
           } else {
             // The input register to the PHI has a subregister:


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