From f318924b28fa2b2bee1c173e86424daff59fce34 Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Fri, 27 Jul 2012 21:21:26 +0000
Subject: [PATCH] Teach CodeGenPrep to look past bitcast when it's duplicating
 return instruction into predecessor blocks to enable tail call optimization.

rdar://11958338

llvm-svn: 160894
---
 lib/Transforms/Scalar/CodeGenPrepare.cpp | 17 ++++-
 lib/Transforms/Utils/BasicBlockUtils.cpp | 24 +++++--
 test/CodeGen/X86/tailcall-cgp-dup.ll     | 87 ++++++++++++++++++++++++
 3 files changed, 121 insertions(+), 7 deletions(-)
 create mode 100644 test/CodeGen/X86/tailcall-cgp-dup.ll

diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp
index f425cd03be6..4b4a8c598fc 100644
--- a/lib/Transforms/Scalar/CodeGenPrepare.cpp
+++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp
@@ -645,10 +645,18 @@ bool CodeGenPrepare::DupRetToEnableTailCallOpts(ReturnInst *RI) {
   if (!TLI)
     return false;
 
+  PHINode *PN = 0;
+  BitCastInst *BCI = 0;
   Value *V = RI->getReturnValue();
-  PHINode *PN = V ? dyn_cast<PHINode>(V) : NULL;
-  if (V && !PN)
-    return false;
+  if (V) {
+    BCI = dyn_cast<BitCastInst>(V);
+    if (BCI)
+      V = BCI->getOperand(0);
+
+    PN = dyn_cast<PHINode>(V);
+    if (!PN)
+      return false;
+  }
 
   BasicBlock *BB = RI->getParent();
   if (PN && PN->getParent() != BB)
@@ -666,6 +674,9 @@ bool CodeGenPrepare::DupRetToEnableTailCallOpts(ReturnInst *RI) {
   if (PN) {
     BasicBlock::iterator BI = BB->begin();
     do { ++BI; } while (isa<DbgInfoIntrinsic>(BI));
+    if (&*BI == BCI)
+      // Also skip over the bitcast.
+      ++BI;
     if (&*BI != RI)
       return false;
   } else {
diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index 55764321491..2679b933f6b 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -659,10 +659,26 @@ ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
   // If the return instruction returns a value, and if the value was a
   // PHI node in "BB", propagate the right value into the return.
   for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
-       i != e; ++i)
-    if (PHINode *PN = dyn_cast<PHINode>(*i))
-      if (PN->getParent() == BB)
-        *i = PN->getIncomingValueForBlock(Pred);
+       i != e; ++i) {
+    Value *V = *i;
+    Instruction *NewBC = 0;
+    if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
+      // Return value might be bitcasted. Clone and insert it before the
+      // return instruction.
+      V = BCI->getOperand(0);
+      NewBC = BCI->clone();
+      Pred->getInstList().insert(NewRet, NewBC);
+      *i = NewBC;
+    }
+    if (PHINode *PN = dyn_cast<PHINode>(V)) {
+      if (PN->getParent() == BB) {
+        if (NewBC)
+          NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
+        else
+          *i = PN->getIncomingValueForBlock(Pred);
+      }
+    }
+  }
       
   // Update any PHI nodes in the returning block to realize that we no
   // longer branch to them.
diff --git a/test/CodeGen/X86/tailcall-cgp-dup.ll b/test/CodeGen/X86/tailcall-cgp-dup.ll
new file mode 100644
index 00000000000..a80b90f9eee
--- /dev/null
+++ b/test/CodeGen/X86/tailcall-cgp-dup.ll
@@ -0,0 +1,87 @@
+; RUN: llc < %s -mtriple=x86_64-apple-darwin | FileCheck %s
+
+; Teach CGP to dup returns to enable tail call optimization.
+; rdar://9147433
+
+define i32 @foo(i32 %x) nounwind ssp {
+; CHECK: foo:
+entry:
+  switch i32 %x, label %return [
+    i32 1, label %sw.bb
+    i32 2, label %sw.bb1
+    i32 3, label %sw.bb3
+    i32 4, label %sw.bb5
+    i32 5, label %sw.bb7
+    i32 6, label %sw.bb9
+  ]
+
+sw.bb:                                            ; preds = %entry
+; CHECK: jmp _f1
+  %call = tail call i32 @f1() nounwind
+  br label %return
+
+sw.bb1:                                           ; preds = %entry
+; CHECK: jmp _f2
+  %call2 = tail call i32 @f2() nounwind
+  br label %return
+
+sw.bb3:                                           ; preds = %entry
+; CHECK: jmp _f3
+  %call4 = tail call i32 @f3() nounwind
+  br label %return
+
+sw.bb5:                                           ; preds = %entry
+; CHECK: jmp _f4
+  %call6 = tail call i32 @f4() nounwind
+  br label %return
+
+sw.bb7:                                           ; preds = %entry
+; CHECK: jmp _f5
+  %call8 = tail call i32 @f5() nounwind
+  br label %return
+
+sw.bb9:                                           ; preds = %entry
+; CHECK: jmp _f6
+  %call10 = tail call i32 @f6() nounwind
+  br label %return
+
+return:                                           ; preds = %entry, %sw.bb9, %sw.bb7, %sw.bb5, %sw.bb3, %sw.bb1, %sw.bb
+  %retval.0 = phi i32 [ %call10, %sw.bb9 ], [ %call8, %sw.bb7 ], [ %call6, %sw.bb5 ], [ %call4, %sw.bb3 ], [ %call2, %sw.bb1 ], [ %call, %sw.bb ], [ 0, %entry ]
+  ret i32 %retval.0
+}
+
+declare i32 @f1()
+
+declare i32 @f2()
+
+declare i32 @f3()
+
+declare i32 @f4()
+
+declare i32 @f5()
+
+declare i32 @f6()
+
+; rdar://11958338
+%0 = type opaque
+
+declare i8* @bar(i8*) uwtable optsize noinline ssp
+
+define hidden %0* @thingWithValue(i8* %self) uwtable ssp {
+entry:
+; CHECK: thingWithValue:
+; CHECK: jmp _bar
+  br i1 undef, label %if.then.i, label %if.else.i
+
+if.then.i:                                        ; preds = %entry
+  br label %someThingWithValue.exit
+
+if.else.i:                                        ; preds = %entry
+  %call4.i = tail call i8* @bar(i8* undef) optsize
+  br label %someThingWithValue.exit
+
+someThingWithValue.exit:                          ; preds = %if.else.i, %if.then.i
+  %retval.0.in.i = phi i8* [ undef, %if.then.i ], [ %call4.i, %if.else.i ]
+  %retval.0.i = bitcast i8* %retval.0.in.i to %0*
+  ret %0* %retval.0.i
+}