[TargetInstrInfo] Fix the implementation of commuteInstruction to match the

comment of the API.

Relaxes the behavior of TargetInstrInfo::commuteInstruction when
TargetInstrInfo::findCommutedOpIndices returns false.

Previously TargetInstrInfo triggered a fatal error in such situation whereas based
on the comment in the API it should just return nullptr. Indeed the only
precondition that should be ensured is that the instruction must be commutable.

llvm-svn: 208371

1 files changed, 2 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/TargetInstrInfo.cpp b/llvm/lib/CodeGen/TargetInstrInfo.cpp
index c4c9c83120f..c3f84c64d7f 100644
--- a/llvm/lib/CodeGen/TargetInstrInfo.cpp
+++ b/llvm/lib/CodeGen/TargetInstrInfo.cpp
@@ -127,10 +127,8 @@ MachineInstr *TargetInstrInfo::commuteInstruction(MachineInstr *MI,
     return nullptr;
   unsigned Idx1, Idx2;
   if (!findCommutedOpIndices(MI, Idx1, Idx2)) {
-    std::string msg;
-    raw_string_ostream Msg(msg);
-    Msg << "Don't know how to commute: " << *MI;
-    report_fatal_error(Msg.str());
+    assert(MI->isCommutable() && "Precondition violation: MI must be commutable.");
+    return nullptr;
   }
 
   assert(MI->getOperand(Idx1).isReg() && MI->getOperand(Idx2).isReg() &&