Add Paul's test case

Author: mysterymath

llvm/test/LTO/Resolution/X86/bcmp-libcall.ll

@@ -0,0 +1,34 @@
+;; This test comes from a real world scenario in LTO, where the
+;; definition of bcmp is deleted because it has no uses, but later instcombine
+;; re-introduces a call to bcmp() as part of SimplifyLibCalls.
+
+; RUN: opt %s -o %t -module-summary -mtriple x86_64-unknown-linux-musl
+; RUN: llvm-lto2 run -o %t2 \
+; RUN:   -r %t,foo,plx \
+; RUN:   -r %t,memcmp,x \
+; RUN:   -r %t,bcmp,pl %t -save-temps
+; RUN: llvm-dis %t2.1.2.internalize.bc -o - | FileCheck %s
+
+define i1 @foo(ptr %0, [2 x i32] %1) {
+  ; CHECK-LABEL: define{{.*}}i1 @foo
+  ; CHECK-NEXT: %size = extractvalue [2 x i32] %1, 1
+  ; CHECK-NEXT: %cmp = {{.*}}call i32 @memcmp
+  ; CHECK-NEXT: %eq = icmp eq i32 %cmp, 0
+  ; CHECK-NEXT: ret i1 %eq
+
+  %size = extractvalue [2 x i32] %1, 1
+  %cmp = call i32 @memcmp(ptr %0, ptr null, i32 %size)
+  %eq = icmp eq i32 %cmp, 0
+  ret i1 %eq
+}
+
+; CHECK: declare i32 @memcmp(ptr, ptr, i32)
+declare i32 @memcmp(ptr, ptr, i32)
+
+;; Ensure bcmp is removed from module. Follow up patches can address this.
+; CHECK-NOT: declare{{.*}}i32 @bcmp
+; CHECK-NOT: define{{.*}}i32 @bcmp
+define i32 @bcmp(ptr %0, ptr %1, i32 %2) {
+  ret i32 0
+}
+