From 05f18920e11f9427201ff3f023d11a8863deac37 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Mon, 1 Dec 2008 02:34:36 +0000
Subject: Teach inst combine to merge GEPs through PHIs.  This is really
 important because it is sinking the loads using the GEPs, but not the GEPs
 themselves.  This triggers 647 times on 403.gcc and makes the .s file much
 much nicer.  For example before:

        je      LBB1_87 ## bb78
LBB1_62:        ## bb77
        leal    84(%esi), %eax
LBB1_63:        ## bb79
        movl    (%eax), %eax
...
LBB1_87:        ## bb78
        movl    $0, 4(%esp)
        movl    %esi, (%esp)
        call    L_make_decl_rtl$stub
        jmp     LBB1_62 ## bb77


after:

        jne     LBB1_63 ## bb79
LBB1_62:        ## bb78
        movl    $0, 4(%esp)
        movl    %esi, (%esp)
        call    L_make_decl_rtl$stub
LBB1_63:        ## bb79
        movl    84(%esi), %eax

The input code was (and the GEPs are merged and
the PHI is now eliminated by instcombine):

        br i1 %tmp233, label %bb78, label %bb77
bb77:
        %tmp234 = getelementptr %struct.tree_node* %t_addr.3, i32 0, i32 0, i32 22
        br label %bb79
bb78:
        call void @make_decl_rtl(%struct.tree_node* %t_addr.3, i8* null) nounwind
        %tmp235 = getelementptr %struct.tree_node* %t_addr.3, i32 0, i32 0, i32 22
        br label %bb79
bb79:
        %iftmp.12.0.in = phi %struct.rtx_def** [ %tmp235, %bb78 ], [ %tmp234, %bb77 ]
        %iftmp.12.0 = load %struct.rtx_def** %iftmp.12.0.in



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60322 91177308-0d34-0410-b5e6-96231b3b80d8
---
 test/Transforms/InstCombine/phi.ll | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

(limited to 'test/Transforms/InstCombine/phi.ll')

diff --git a/test/Transforms/InstCombine/phi.ll b/test/Transforms/InstCombine/phi.ll
index 6f0ef6b549..4efbb79d9d 100644
--- a/test/Transforms/InstCombine/phi.ll
+++ b/test/Transforms/InstCombine/phi.ll
@@ -1,7 +1,6 @@
 ; This test makes sure that these instructions are properly eliminated.
 ;
 ; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep phi
-; END.
 
 define i32 @test1(i32 %A, i1 %b) {
 BB0:
@@ -98,4 +97,19 @@ Exit:           ; preds = %Loop
         ret i32 0
 }
 
+define i32* @test8({ i32, i32 } *%A, i1 %b) {
+BB0:
+        %X = getelementptr { i32, i32 } *%A, i32 0, i32 1
+        br i1 %b, label %BB1, label %BB2
+
+BB1:
+        %Y = getelementptr { i32, i32 } *%A, i32 0, i32 1
+        br label %BB2
+
+BB2:
+        ;; Suck GEPs into phi
+        %B = phi i32* [ %X, %BB0 ], [ %Y, %BB1 ]
+        ret i32* %B
+}
+
 
-- 
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