Don't insert lifetime.end markers between a musttail call and ret

The allocas going out of scope are immediately killed by the return
instruction.

This is a resend of r208912, which was committed accidentally.

Reviewers: chandlerc

Differential Revision: http://reviews.llvm.org/D3792

llvm-svn: 208920

llvm/lib/Transforms/Utils/InlineFunction.cpp

@@ -755,8 +755,13 @@ bool llvm::InlineFunction(CallSite CS, InlineFunctionInfo &IFI,
       }
 
       builder.CreateLifetimeStart(AI, AllocaSize);
-      for (ReturnInst *RI : Returns)
+      for (ReturnInst *RI : Returns) {
+        // Don't insert llvm.lifetime.end calls between a musttail call and a
+        // return.  The return kills all local allocas.
+        if (InlinedMustTailCalls && getPrecedingMustTailCall(RI))
+          continue;
         IRBuilder<>(RI).CreateLifetimeEnd(AI, AllocaSize);
+      }
     }
   }
 
@@ -774,8 +779,13 @@ bool llvm::InlineFunction(CallSite CS, InlineFunctionInfo &IFI,
 
     // Insert a call to llvm.stackrestore before any return instructions in the
     // inlined function.
-    for (ReturnInst *RI : Returns)
+    for (ReturnInst *RI : Returns) {
+      // Don't insert llvm.stackrestore calls between a musttail call and a
+      // return.  The return will restore the stack pointer.
+      if (InlinedMustTailCalls && getPrecedingMustTailCall(RI))
+        continue;
       IRBuilder<>(RI).CreateCall(StackRestore, SavedPtr);
+    }
   }
 
   // If we are inlining for an invoke instruction, we must make sure to rewrite

llvm/test/Transforms/Inline/inline-tail.ll

@@ -49,6 +49,42 @@ define void @test_musttail_basic_a(i32* %p) {
   ret void
 }
 
+; Don't insert lifetime end markers here, the lifetime is trivially over due
+; the return.
+; CHECK: define void @test_byval_a(
+; CHECK: musttail call void @test_byval_c(
+; CHECK-NEXT: ret void
+
+declare void @test_byval_c(i32* byval %p)
+define internal void @test_byval_b(i32* byval %p) {
+  musttail call void @test_byval_c(i32* byval %p)
+  ret void
+}
+define void @test_byval_a(i32* byval %p) {
+  musttail call void @test_byval_b(i32* byval %p)
+  ret void
+}
+
+; Don't insert a stack restore, we're about to return.
+; CHECK: define void @test_dynalloca_a(
+; CHECK: call i8* @llvm.stacksave(
+; CHECK: alloca i8, i32 %n
+; CHECK: musttail call void @test_dynalloca_c(
+; CHECK-NEXT: ret void
+
+declare void @escape(i8* %buf)
+declare void @test_dynalloca_c(i32* byval %p, i32 %n)
+define internal void @test_dynalloca_b(i32* byval %p, i32 %n) alwaysinline {
+  %buf = alloca i8, i32 %n              ; dynamic alloca
+  call void @escape(i8* %buf)           ; escape it
+  musttail call void @test_dynalloca_c(i32* byval %p, i32 %n)
+  ret void
+}
+define void @test_dynalloca_a(i32* byval %p, i32 %n) {
+  musttail call void @test_dynalloca_b(i32* byval %p, i32 %n)
+  ret void
+}
+
 ; We can't merge the returns.
 ; CHECK: define void @test_multiret_a(
 ; CHECK: musttail call void @test_multiret_c(