ThinLTO: Don't import aliases of any kind (even linkonce_odr)

Summary:
Until a more advanced version of importing can be implemented for
aliases (one that imports an alias as an available_externally definition
of the aliasee), skip the narrow subset of cases that was possible but
came at a cost: aliases of linkonce_odr functions could be imported
because the linkonce_odr function could be safely duplicated from the
source module. This came/comes at the cost of not being able to 'home'
imported linkonce functions (they had to be emitted linkonce_odr in all
the destination modules (even if they weren't used by an alias) rather
than as available_externally - causing extra object size).

Tangentially, this also was the only reason ThinLTO would emit multiple
CUs in to the resulting DWARF - which happens to be a problem for
Fission (there's a fix for this in GDB but not released yet, etc).
(actually it's not the only reason - but I'm sending a patch to fix the
other reason shortly)

There's no reason to believe this particularly narrow alias importing
was especially/meaningfully important, only that it was /possible/ to
implement in this way. When a more general solution is done, it should
still satisfy the DWARF concerns above, since the import will still be
available_externally, and thus not create extra CUs.

Since now all aliases are treated the same, I removed/simplified some
test cases since they were testing corner cases where there are no
longer any corners.

Reviewers: tejohnson, mehdi_amini

Differential Revision: https://reviews.llvm.org/D35875

llvm-svn: 309278

1 files changed, 3 insertions, 6 deletions

diff --git a/llvm/test/Transforms/FunctionImport/funcimport.ll b/llvm/test/Transforms/FunctionImport/funcimport.ll
index cc732a3bd98..1aafd00318c 100644
--- a/llvm/test/Transforms/FunctionImport/funcimport.ll
+++ b/llvm/test/Transforms/FunctionImport/funcimport.ll
@@ -40,12 +40,9 @@ declare void @weakalias(...) #1
 ; CHECK-DAG: declare void @analias
 declare void @analias(...) #1
 
-; Aliases import the aliasee function
+; Aliases are not imported
 declare void @linkoncealias(...) #1
-; INSTLIMDEF-DAG: Import linkoncealias
-; INSTLIMDEF-DAG: Import linkoncefunc
-; CHECK-DAG: define linkonce_odr void @linkoncefunc()
-; CHECK-DAG: @linkoncealias = alias void (...), bitcast (void ()* @linkoncefunc to void (...)*
+; CHECK-DAG: declare void @linkoncealias(...)
 
 ; INSTLIMDEF-DAG: Import referencestatics
 ; INSTLIMDEF-DAG: define available_externally i32 @referencestatics(i32 %i) !thinlto_src_module !0 {
@@ -108,7 +105,7 @@ declare void @linkoncefunc2(...) #1
 declare void @variadic(...)
 
 ; INSTLIMDEF-DAG: Import globalfunc2
-; INSTLIMDEF-DAG: 13 function-import - Number of functions imported
+; INSTLIMDEF-DAG: 11 function-import - Number of functions imported
 ; CHECK-DAG: !0 = !{!"{{.*}}/Inputs/funcimport.ll"}
 
 ; The actual GUID values will depend on path to test.