From f59e4e34528a078c2db57ee72b2814b495989124 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 1 Jun 2012 05:29:15 +0000
Subject: enhance the logic for looking through tailcalls to look through
 transparent casts in multiple-return value scenarios, like what happens on
 X86-64 when returning small structs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157800 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/Analysis.cpp        | 22 +++++++++++++++++++-
 test/CodeGen/X86/tailcall-64.ll | 46 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 1 deletion(-)

diff --git a/lib/CodeGen/Analysis.cpp b/lib/CodeGen/Analysis.cpp
index dd11d15975..1a8968dd28 100644
--- a/lib/CodeGen/Analysis.cpp
+++ b/lib/CodeGen/Analysis.cpp
@@ -322,7 +322,27 @@ bool llvm::isInTailCallPosition(ImmutableCallSite CS, Attributes CalleeRetAttr,
     return false;
 
   // Otherwise, make sure the unmodified return value of I is the return value.
-  return getNoopInput(Ret->getOperand(0), TLI) == I;
+  // We handle two cases: multiple return values + scalars.
+  Value *RetVal = Ret->getOperand(0);
+  if (!isa<InsertValueInst>(RetVal) || !isa<StructType>(RetVal->getType()))
+    // Handle scalars first.
+    return getNoopInput(Ret->getOperand(0), TLI) == I;
+  
+  // If this is an aggregate return, look through the insert/extract values and
+  // see if each is transparent.
+  for (unsigned i = 0, e =cast<StructType>(RetVal->getType())->getNumElements();
+       i != e; ++i) {
+    const Value *InScalar = getNoopInput(FindInsertedValue(RetVal, i), TLI);
+    
+    // If the scalar value being inserted is an extractvalue of the right index
+    // from the call, then everything is good.
+    const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(InScalar);
+    if (EVI == 0 || EVI->getOperand(0) != I || EVI->getNumIndices() != 1 ||
+        EVI->getIndices()[0] != i)
+      return false;
+  }
+  
+  return true;
 }
 
 bool llvm::isInTailCallPosition(SelectionDAG &DAG, SDNode *Node,
diff --git a/test/CodeGen/X86/tailcall-64.ll b/test/CodeGen/X86/tailcall-64.ll
index a3ef2dc8ef..98e728c909 100644
--- a/test/CodeGen/X86/tailcall-64.ll
+++ b/test/CodeGen/X86/tailcall-64.ll
@@ -41,3 +41,49 @@ define <4 x i32> @test_vectorbitcast() {
 }
 ; CHECK: test_vectorbitcast:
 ; CHECK: jmp	_testv                  ## TAILCALL
+
+
+declare { i64, i64 } @testp()
+
+define {i64, i64} @test_pair_trivial() {
+  %A = tail call { i64, i64} @testp()
+  ret { i64, i64} %A
+}
+; CHECK: test_pair_trivial:
+; CHECK: jmp	_testp                  ## TAILCALL
+
+
+
+define {i64, i64} @test_pair_trivial_extract() {
+  %A = tail call { i64, i64} @testp()
+  %x = extractvalue { i64, i64} %A, 0
+  %y = extractvalue { i64, i64} %A, 1
+  
+  %b = insertvalue {i64, i64} undef, i64 %x, 0
+  %c = insertvalue {i64, i64} %b, i64 %y, 1
+  
+  ret { i64, i64} %c
+}
+
+; CHECK: test_pair_trivial_extract:
+; CHECK: jmp	_testp                  ## TAILCALL
+
+define {i8*, i64} @test_pair_conv_extract() {
+  %A = tail call { i64, i64} @testp()
+  %x = extractvalue { i64, i64} %A, 0
+  %y = extractvalue { i64, i64} %A, 1
+  
+  %x1 = inttoptr i64 %x to i8*
+  
+  %b = insertvalue {i8*, i64} undef, i8* %x1, 0
+  %c = insertvalue {i8*, i64} %b, i64 %y, 1
+  
+  ret { i8*, i64} %c
+}
+
+; CHECK: test_pair_conv_extract:
+; CHECK: jmp	_testp                  ## TAILCALL
+
+
+
+
-- 
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