Merging r339636:

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r339636 | rnk | 2018-08-13 18:24:35 -0700 (Mon, 13 Aug 2018) | 17 lines

[BasicAA] Don't assume tail calls with byval don't alias allocas

Summary:
Calls marked 'tail' cannot read or write allocas from the current frame
because the current frame might be destroyed by the time they run.
However, a tail call may use an alloca with byval. Calling with byval
copies the contents of the alloca into argument registers or stack
slots, so there is no lifetime issue. Tail calls never modify allocas,
so we can return just ModRefInfo::Ref.

Fixes PR38466, a longstanding bug.

Reviewers: hfinkel, nlewycky, gbiv, george.burgess.iv

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D50679
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_70@339698 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 38 insertions, 0 deletions

diff --git a/test/Analysis/BasicAA/tail-byval.ll b/test/Analysis/BasicAA/tail-byval.ll
new file mode 100644
index 00000000000..0aa8dfdaedf
--- /dev/null
+++ b/test/Analysis/BasicAA/tail-byval.ll
@@ -0,0 +1,15 @@
+; RUN: opt -basicaa -aa-eval -print-all-alias-modref-info -disable-output < %s 2>&1 | FileCheck %s
+
+declare void @takebyval(i32* byval %p)
+
+define i32 @tailbyval() {
+entry:
+  %p = alloca i32
+  store i32 42, i32* %p
+  tail call void @takebyval(i32* byval %p)
+  %rv = load i32, i32* %p
+  ret i32 %rv
+}
+; FIXME: This should be Just Ref.
+; CHECK-LABEL: Function: tailbyval: 1 pointers, 1 call sites
+; CHECK-NEXT:   Both ModRef:  Ptr: i32* %p       <->  tail call void @takebyval(i32* byval %p)
diff --git a/test/Transforms/DeadStoreElimination/tail-byval.ll b/test/Transforms/DeadStoreElimination/tail-byval.ll
new file mode 100644
index 00000000000..ed2fbd434a7
--- /dev/null
+++ b/test/Transforms/DeadStoreElimination/tail-byval.ll
@@ -0,0 +1,23 @@
+; RUN: opt -dse -S < %s | FileCheck %s
+
+; Don't eliminate stores to allocas before tail calls to functions that use
+; byval. It's correct to mark calls like these as 'tail'. To implement this tail
+; call, the backend should copy the bytes from the alloca into the argument area
+; before clearing the stack.
+
+target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128"
+target triple = "i386-unknown-linux-gnu"
+
+declare void @g(i32* byval %p)
+
+define void @f(i32* byval %x) {
+entry:
+  %p = alloca i32
+  %v = load i32, i32* %x
+  store i32 %v, i32* %p
+  tail call void @g(i32* byval %p)
+  ret void
+}
+; CHECK-LABEL: define void @f(i32* byval %x)
+; CHECK:   store i32 %v, i32* %p
+; CHECK:   tail call void @g(i32* byval %p)