From 7e20a574eb3f4fc3840a0490c814443d756e2e0e Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Wed, 11 May 2011 01:03:01 +0000
Subject: Add a late optimization to BranchFolding that hoist common
 instruction sequences at the start of basic blocks to their common
 predecessor. It's actually quite common (e.g. about 50 times in JM/lencod)
 and has shown to be a nice code size benefit. e.g.

        pushq   %rax
        testl   %edi, %edi
        jne     LBB0_2
## BB#1:
        xorb    %al, %al
        popq    %rdx
        ret
LBB0_2:
        xorb    %al, %al
        callq   _foo
        popq    %rdx
        ret

=>

        pushq   %rax
        xorb    %al, %al
        testl   %edi, %edi
        je      LBB0_2
## BB#1:
        callq   _foo
LBB0_2:
        popq    %rdx
        ret

rdar://9145558


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131172 91177308-0d34-0410-b5e6-96231b3b80d8
---
 test/CodeGen/X86/hoist-common.ll | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 test/CodeGen/X86/hoist-common.ll

(limited to 'test')

diff --git a/test/CodeGen/X86/hoist-common.ll b/test/CodeGen/X86/hoist-common.ll
new file mode 100644
index 0000000..2b1550a
--- /dev/null
+++ b/test/CodeGen/X86/hoist-common.ll
@@ -0,0 +1,28 @@
+; RUN: llc < %s -march=x86-64  | FileCheck %s
+
+; Common "xorb al, al" instruction in the two successor blocks should be
+; moved to the entry block above the test + je.
+
+; rdar://9145558
+
+define zeroext i1 @t(i32 %c) nounwind ssp {
+entry:
+; CHECK: t:
+; CHECK: xorb %al, %al
+; CHECK: test
+; CHECK: je
+  %tobool = icmp eq i32 %c, 0
+  br i1 %tobool, label %return, label %if.then
+
+if.then:
+; CHECK: callq
+  %call = tail call zeroext i1 (...)* @foo() nounwind
+  br label %return
+
+return:
+; CHECK: ret
+  %retval.0 = phi i1 [ %call, %if.then ], [ false, %entry ]
+  ret i1 %retval.0
+}
+
+declare zeroext i1 @foo(...)
-- 
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