Bitcode: Add a string table to the bitcode format.

Add a top-level STRTAB block containing a string table blob, and start storing
strings for module codes FUNCTION, GLOBALVAR, ALIAS, IFUNC and COMDAT in
the string table.

This change allows us to share names between globals and comdats as well
as between modules, and improves the efficiency of loading bitcode files by
no longer using a bit encoding for symbol names. Once we start writing the
irsymtab to the bitcode file we will also be able to share strings between
it and the module.

On my machine, link time for Chromium for Linux with ThinLTO decreases by
about 7% for no-op incremental builds or about 1% for full builds. Total
bitcode file size decreases by about 3%.

As discussed on llvm-dev:
http://lists.llvm.org/pipermail/llvm-dev/2017-April/111732.html

Differential Revision: https://reviews.llvm.org/D31838

llvm-svn: 300464

1 files changed, 17 insertions, 19 deletions

diff --git a/llvm/test/Bitcode/thinlto-alias.ll b/llvm/test/Bitcode/thinlto-alias.ll
index cfdf8f7b0bd..2c235f0620e 100644
--- a/llvm/test/Bitcode/thinlto-alias.ll
+++ b/llvm/test/Bitcode/thinlto-alias.ll
@@ -5,33 +5,31 @@
 ; RUN: llvm-lto -thinlto -o %t3 %t.o %t2.o
 ; RUN: llvm-bcanalyzer -dump %t3.thinlto.bc | FileCheck %s --check-prefix=COMBINED
 
+; CHECK: <SOURCE_FILENAME
+; "main"
+; CHECK-NEXT: <FUNCTION op0=0 op1=4
+; "analias"
+; CHECK-NEXT: <FUNCTION op0=4 op1=7
 ; CHECK:       <GLOBALVAL_SUMMARY_BLOCK
 ; CHECK-NEXT:    <VERSION
-; See if the call to func is registered, using the expected callsite count
-; and value id matching the subsequent value symbol table.
-; CHECK-NEXT:    <PERMODULE {{.*}} op4=[[FUNCID:[0-9]+]]/>
+; See if the call to func is registered.
+; The value id 1 matches the second FUNCTION record above.
+; CHECK-NEXT:    <PERMODULE {{.*}} op4=1/>
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
-; CHECK-NEXT:  <VALUE_SYMTAB
-; CHECK-NEXT:    <FNENTRY {{.*}} record string = 'main'
-; External function analias should have entry with value id FUNCID
-; CHECK-NEXT:    <ENTRY {{.*}} op0=[[FUNCID]] {{.*}} record string = 'analias'
-; CHECK-NEXT:  </VALUE_SYMTAB>
+
+; CHECK: <STRTAB_BLOCK
+; CHECK-NEXT: blob data = 'mainanalias'
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
-; See if the call to analias is registered, using the expected callsite count
-; and value id matching the subsequent value symbol table.
-; COMBINED-NEXT:    <COMBINED {{.*}} op5=[[ALIASID:[0-9]+]]/>
-; Followed by the alias and aliasee
+; See if the call to analias is registered, using the expected value id.
+; COMBINED-NEXT:    <VALUE_GUID op0=[[ALIASID:[0-9]+]] op1=-5751648690987223394/>
+; COMBINED-NEXT:    <VALUE_GUID
+; COMBINED-NEXT:    <VALUE_GUID op0=[[ALIASEEID:[0-9]+]] op1=-1039159065113703048/>
+; COMBINED-NEXT:    <COMBINED {{.*}} op5=[[ALIASID]]/>
 ; COMBINED-NEXT:    <COMBINED {{.*}}
-; COMBINED-NEXT:    <COMBINED_ALIAS  {{.*}} op3=[[ALIASEEID:[0-9]+]]
+; COMBINED-NEXT:    <COMBINED_ALIAS  {{.*}} op3=[[ALIASEEID]]
 ; COMBINED-NEXT:  </GLOBALVAL_SUMMARY_BLOCK
-; COMBINED-NEXT:  <VALUE_SYMTAB
-; Entry for function func should have entry with value id ALIASID
-; COMBINED-NEXT:    <COMBINED_ENTRY {{.*}} op0=[[ALIASID]] op1=-5751648690987223394/>
-; COMBINED-NEXT:    <COMBINED
-; COMBINED-NEXT:    <COMBINED_ENTRY {{.*}} op0=[[ALIASEEID]] op1=-1039159065113703048/>
-; COMBINED-NEXT:  </VALUE_SYMTAB>
 
 ; ModuleID = 'thinlto-function-summary-callgraph.ll'
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"