Make GlobalOpt's GV-by-alloca replacement work for PNaCl.

GlobalOpt currently assumes only an external "main" is the "real main".
This is no longer the case for PNaCl, where we internalize "main". Make
the test more strict and PNaCl specific by checking that "main" is just
used once - in a call from "_start", but does not have to be external.

Note that this also addresses a possible bug in the optimization for C
code, since C does not guarantee that main is not recursive.

This CL's purpose is to address a SPEC performance regression - 10% in
183.equake. The regression appeared after our ABI change that made 'main'
internal, which disabled this particular optimization. The CL addresses
this by re-enabling the optimization and also being more C-standard
conforming.

BUG=None

Review URL: https://codereview.chromium.org/18615015

2 files changed, 38 insertions, 0 deletions

diff --git a/test/NaCl/Localmods/lit.local.cfg b/test/NaCl/Localmods/lit.local.cfg
new file mode 100644
index 0000000000..c6106e4746
--- /dev/null
+++ b/test/NaCl/Localmods/lit.local.cfg
@@ -0,0 +1 @@
+config.suffixes = ['.ll']
diff --git a/test/NaCl/Localmods/test-globalopt-main.ll b/test/NaCl/Localmods/test-globalopt-main.ll
new file mode 100644
index 0000000000..90d0e3193c
--- /dev/null
+++ b/test/NaCl/Localmods/test-globalopt-main.ll
@@ -0,0 +1,37 @@
+; RUN: opt < %s -globalopt -S | FileCheck %s
+
+; Check that our LOCALMOD for the GlobalOpt optimization is working properly.
+; The user code entry point is a function named main that has a single user:
+; a call from _start.
+; @globchar can be folded into an alloca inside @main, and the global can be
+; deleted.
+
+@globchar = internal global i8* null, align 8
+; CHECK-NOT: @globchar = internal global
+
+define internal i32 @main(i32 %argc, i8** %argv) {
+  ; CHECK: @main(i32
+entry:
+  ; CHECK: %globchar = alloca i8*
+  %argc.addr = alloca i32, align 4
+  %argv.addr = alloca i8**, align 8
+  store i32 %argc, i32* %argc.addr, align 4
+  store i8** %argv, i8*** %argv.addr, align 8
+  %0 = load i8*** %argv.addr, align 8
+  %arrayidx = getelementptr inbounds i8** %0, i64 0
+  %1 = load i8** %arrayidx, align 8
+  store i8* %1, i8** @globchar, align 8
+  %2 = load i8** @globchar, align 8
+  %arrayidx1 = getelementptr inbounds i8* %2, i64 1
+  %3 = load i8* %arrayidx1, align 1
+  call void @somefunc(i8 signext %3)
+  ret i32 0
+}
+
+define i32 @_start(i32 %argc, i8** %argv) {
+  %rv = call i32 @main(i32 %argc, i8** %argv)
+  ret i32 %rv
+}
+
+declare void @somefunc(i8 signext)
+