Recommit r52459, rewriting of the dead argument elimination pass.

This is a fixed version that no longer uses multimap::equal_range, which
resulted in a pointer invalidation problem.

Also, DAE::InspectedFunctions was not really necessary, so it got removed.

Lastly, this version no longer applies the extra arg hack on functions who did
not have any arguments to start with.

llvm-svn: 52532

llvm/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
+}