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

[Reid Kleckner]

Hi chandlerc,

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

http://reviews.llvm.org/D3630

Files:
  lib/Transforms/Utils/InlineFunction.cpp
  test/Transforms/Inline/inline-tail.ll

Index: lib/Transforms/Utils/InlineFunction.cpp
===================================================================
--- lib/Transforms/Utils/InlineFunction.cpp
+++ lib/Transforms/Utils/InlineFunction.cpp
@@ -741,8 +741,13 @@
       }
 
       builder.CreateLifetimeStart(AI, AllocaSize);
-      for (ReturnInst *RI : Returns)
+      for (ReturnInst *RI : Returns) {
+        // Don't insert lifetime.end calls after a musttail call, the allocas
+        // are trivially dead.
+        if (InlinedMustTailCalls && isPrecededByMustTailCall(RI))
+          continue;
         IRBuilder<>(RI).CreateLifetimeEnd(AI, AllocaSize);
+      }
     }
   }
 
Index: test/Transforms/Inline/inline-tail.ll
===================================================================
--- test/Transforms/Inline/inline-tail.ll
+++ test/Transforms/Inline/inline-tail.ll
@@ -49,6 +49,42 @@
   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(
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