[PATCH] Teach the inliner how to preserve musttail invariants

[Reid Kleckner]

================
Comment at: lib/Transforms/Utils/InlineFunction.cpp:697
@@ +696,3 @@
+      for (Instruction &I : *BB) {
+        if (CallInst *CI = dyn_cast<CallInst>(&I)) {
+          CallInst::TailCallKind ChildTCK = CI->getTailCallKind();
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Chandler Carruth wrote:
> nit: invert and use continue to reduce indentation
done

================
Comment at: lib/Transforms/Utils/InlineFunction.cpp:794
@@ +793,3 @@
+
+      if (NeedBitCast) {
+        // Strip any possible inlined bitcast and grab the musttail call.
----------------
Chandler Carruth wrote:
> nit: as above, invert and continue to reduce indentation.
done

================
Comment at: lib/Transforms/Utils/InlineFunction.cpp:795-800
@@ +794,8 @@
+      if (NeedBitCast) {
+        // Strip any possible inlined bitcast and grab the musttail call.
+        Value *RV = RI->getReturnValue();
+        BitCastInst *OldCast = dyn_cast<BitCastInst>(RV);
+        if (OldCast)
+          RV = OldCast->getOperand(0);
+        assert(cast<CallInst>(RV)->isMustTailCall());
+
----------------
Chandler Carruth wrote:
> Rather than duplicating isPrecededByMustTailCall, make that function getPrecedingMustTailCallInst or some such, and have it return null when there is no call? That should make this loop simplify quite a bit.
Sure.  It helps a bit, but I have to get the bitcast instr so I can erase it.

http://reviews.llvm.org/D3491