Fix a pretty serious misfeature of the inliner: if it inlines a function

with multiple return values it inserts a PHI to merge them all together.
However, if the return values are all the same, it ends up with a pointless
PHI and this pointless PHI happens to really block SRoA from happening in 
at least a silly C++ example written by Doug, but probably others.  This 
fixes rdar://7339069.

llvm-svn: 85206

llvm/lib/Transforms/Utils/InlineFunction.cpp

@@ -619,8 +619,17 @@ bool llvm::InlineFunction(CallSite CS, CallGraph *CG, const TargetData *TD,
                "Ret value not consistent in function!");
         PHI->addIncoming(RI->getReturnValue(), RI->getParent());
       }
+    
+      // Now that we inserted the PHI, check to see if it has a single value
+      // (e.g. all the entries are the same or undef).  If so, remove the PHI so
+      // it doesn't block other optimizations.
+      if (Value *V = PHI->hasConstantValue()) {
+        PHI->replaceAllUsesWith(V);
+        PHI->eraseFromParent();
+      }
     }
 
+
     // Add a branch to the merge points and remove return instructions.
     for (unsigned i = 0, e = Returns.size(); i != e; ++i) {
       ReturnInst *RI = Returns[i];

llvm/test/Transforms/Inline/basictest.ll

@@ -1,4 +1,4 @@
-; RUN: opt < %s -inline -S | FileCheck %s
+; RUN: opt < %s -inline -scalarrepl -S | FileCheck %s
 
 define i32 @test1f(i32 %i) {
         ret i32 %i
@@ -13,3 +13,34 @@ define i32 @test1(i32 %W) {
 ; CHECK-NEXT: ret i32 %Y
 }
 
+
+
+; rdar://7339069
+
+%T = type { i32, i32 }
+
+; CHECK-NOT: @test2f
+define internal %T* @test2f(i1 %cond, %T* %P) {
+  br i1 %cond, label %T, label %F
+  
+T:
+  %A = getelementptr %T* %P, i32 0, i32 0
+  store i32 42, i32* %A
+  ret %T* %P
+  
+F:
+  ret %T* %P
+}
+
+define i32 @test2(i1 %cond) {
+  %A = alloca %T
+  
+  %B = call %T* @test2f(i1 %cond, %T* %A)
+  %C = getelementptr %T* %B, i32 0, i32 0
+  %D = load i32* %C
+  ret i32 %D
+  
+; CHECK: @test2(
+; CHECK-NOT: = alloca
+; CHECK: ret i32 42
+}