[ThinLTO] Prevent importing of "llvm.used" values

Summary:
This patch prevents importing from (and therefore exporting from) any
module with a "llvm.used" local value. Local values need to be promoted
and renamed when importing, and their presense on the llvm.used variable
indicates that there are opaque uses that won't see the rename. One such
example is a use in inline assembly.

See also the discussion at:
http://lists.llvm.org/pipermail/llvm-dev/2016-April/098047.html

As part of this, move collectUsedGlobalVariables out of Transforms/Utils
and into IR/Module so that it can be used more widely. There are several
other places in LLVM that used copies of this code that can be cleaned
up as a follow on NFC patch.

Reviewers: joker.eph

Subscribers: pcc, llvm-commits, joker.eph

Differential Revision: http://reviews.llvm.org/D18986

llvm-svn: 266877

1 files changed, 19 insertions, 0 deletions

diff --git a/llvm/test/Transforms/FunctionImport/inlineasm.ll b/llvm/test/Transforms/FunctionImport/inlineasm.ll
new file mode 100644
index 00000000000..d0516f14653
--- /dev/null
+++ b/llvm/test/Transforms/FunctionImport/inlineasm.ll
@@ -0,0 +1,19 @@
+; Do setup work for all below tests: generate bitcode and combined index
+; RUN: opt -module-summary %s -o %t.bc
+; RUN: opt -module-summary %p/Inputs/inlineasm.ll -o %t2.bc
+; RUN: llvm-lto -thinlto -o %t3 %t.bc %t2.bc
+
+; Attempt the import now, ensure below that file containing inline assembly
+; is not imported from. Otherwise we would need to promote its local variable
+; used in the inline assembly, which would not see the rename.
+; RUN: opt -function-import -summary-file %t3.thinlto.bc %t.bc -S 2>&1 | FileCheck %s --check-prefix=CHECK
+
+define i32 @main() #0 {
+entry:
+  %f = alloca i64, align 8
+  call void @foo(i64* %f)
+  ret i32 0
+}
+
+; CHECK: declare void @foo(i64*)
+declare void @foo(i64*) #1