Rewrite the DeadArgumentElimination pass, to use a more explicit tracking of

dependencies between return values and/or arguments. Also make the handling of
arguments and return values the same.

The pass now looks properly inside returned structs, but only at the first                                                                                     
level (ie, not inside nested structs).

Also add a testcase for testing various variations of (multiple) dead rerturn
values.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52459 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/DeadArgElim/multdeadretval.ll

@@ -0,0 +1,39 @@
+; This test sees if return values (and arguments) are properly removed when they
+; are unused. All unused values are typed i16, so we can easily check. We also
+; run instcombine to fold insert/extractvalue chains and we run dce to clean up
+; any remaining dead stuff.
+; RUN: llvm-as < %s | opt -deadargelim -instcombine -dce | llvm-dis | not grep i16
+
+define internal {i16, i32} @test(i16 %DEADARG) {
+        %A = insertvalue {i16,i32} undef, i16 1, 0
+        %B = insertvalue {i16,i32} %A, i32 1001, 1
+        ret {i16,i32} %B
+}
+
+define internal {i32, i16} @test2() {
+        %DEAD = call i16 @test4()
+        %A = insertvalue {i32,i16} undef, i32 1, 0
+        %B = insertvalue {i32,i16} %A, i16 %DEAD, 1
+        ret {i32,i16} %B
+}
+
+define internal i32 @test3(i16 %A) {
+        %ret = call {i16, i32} @test( i16 %A )                ; <i32> [#uses=0]
+        %DEAD = extractvalue {i16, i32} %ret, 0
+        %LIVE = extractvalue {i16, i32} %ret, 1
+        ret i32 %LIVE
+}
+
+define internal i16 @test4() {
+        ret i16 0
+}
+
+define i32 @main() {
+        %ret = call {i32, i16} @test2()                ; <i32> [#uses=1]
+        %LIVE = extractvalue {i32, i16} %ret, 0
+        %DEAD = extractvalue {i32, i16} %ret, 1
+        %Y = add i32 %LIVE, -123           ; <i32> [#uses=1]
+        %LIVE2 = call i32 @test3(i16 %DEAD)                ; <i32> [#uses=1]
+        %Z = add i32 %LIVE2, %Y           ; <i32> [#uses=1]
+        ret i32 %Z
+}