LTO: Include live bit in ThinLTO cache key.

As of r323633, this bit started controlling whether symbol definitions
appear in object files, and it also became sensitive to the prevailing
bit, so it needs to be included in the key.

Differential Revision: https://reviews.llvm.org/D43109

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@324711 91177308-0d34-0410-b5e6-96231b3b80d8

Author: pcc

lib/LTO/LTO.cpp

@@ -177,6 +177,7 @@ static void computeCacheKey(
 
   auto AddUsedThings = [&](GlobalValueSummary *GS) {
     if (!GS) return;
+    AddUnsigned(GS->isLive());
     for (const ValueInfo &VI : GS->refs()) {
       AddUnsigned(VI.isDSOLocal());
       AddUsedCfiGlobal(VI.getGUID());

test/LTO/Resolution/X86/cache-prevailing.ll

@@ -0,0 +1,18 @@
+; Tests whether the cache is sensitive to the prevailing bit.
+; RUN: rm -rf %t.cache
+; RUN: opt -module-hash -module-summary -o %t.bc %s
+; RUN: llvm-lto2 run -o %t.o %t.bc -cache-dir %t.cache \
+; RUN:   -r %t.bc,foo,p -r %t.bc,bar,px
+; RUN: llvm-lto2 run -o %t.o %t.bc -cache-dir %t.cache \
+; RUN:   -r %t.bc,foo, -r %t.bc,bar,px
+; RUN: ls %t.cache | count 2
+
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.11.0"
+
+@foo = linkonce_odr constant i32 1, comdat
+$foo = comdat any
+
+define i32* @bar() {
+  ret i32* @foo
+}