Correctly preserve the input chain for potential tailcall nodes whose

return values are bitcasts.

The chain had previously been being clobbered with the entry node to
the dag, which sometimes caused other code in the function to be
erroneously deleted when tailcall optimization kicked in.

<rdar://problem/13827621>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181696 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM/ARMISelLowering.cpp

@@ -2147,7 +2147,7 @@ bool ARMTargetLowering::isUsedByReturnOnly(SDNode *N, SDValue &Chain) const {
     Copy = *Copy->use_begin();
     if (Copy->getOpcode() != ISD::CopyToReg || !Copy->hasNUsesOfValue(1, 0))
       return false;
-    Chain = Copy->getOperand(0);
+    TCChain = Copy->getOperand(0);
   } else {
     return false;
   }

test/CodeGen/ARM/call-tc.ll

@@ -162,3 +162,20 @@ define i32 @t9() nounwind {
 declare %class.MutexLock* @_ZN9MutexLockC1Ev(%class.MutexLock*) unnamed_addr nounwind align 2
 
 declare %class.MutexLock* @_ZN9MutexLockD1Ev(%class.MutexLock*) unnamed_addr nounwind align 2
+
+; rdar://13827621
+; Correctly preserve the input chain for the tailcall node in the bitcast case,
+; otherwise the call to floorf is lost.
+define float @libcall_tc_test2(float* nocapture %a, float %b) {
+; CHECKT2D: libcall_tc_test2:
+; CHECKT2D: blx _floorf
+; CHECKT2D: b.w _truncf
+  %1 = load float* %a, align 4
+  %call = tail call float @floorf(float %1)
+  store float %call, float* %a, align 4
+  %call1 = tail call float @truncf(float %b)
+  ret float %call1
+}
+
+declare float @floorf(float) readnone
+declare float @truncf(float) readnone