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d2d01d1984
When eliminating or merging almost empty basic blocks, the existence of non-trivial PHI nodes
is currently used to recognize potential loops of which the block is the header and keep the block.
However, the current algorithm fails if the loops' exit condition is evaluated only with volatile
values hence no PHI nodes in the header. Especially when such a loop is an outer loop of a nested
loop, the loop is collapsed into a single loop which prevent later optimizations from being
applied (e.g., transforming nested loops into simplified forms and loop vectorization).
The patch augments the existing PHI node-based check by adding a pre-test if the BB actually
belongs to a set of loop headers and not eliminating it if yes.
llvm-svn: 264697
257 lines
6.8 KiB
LLVM
257 lines
6.8 KiB
LLVM
; Test merging of blocks with phi nodes.
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;
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; RUN: opt < %s -simplifycfg -S > %t
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; RUN: not grep N: %t
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; RUN: not grep X: %t
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; RUN: not grep 'switch i32[^U]+%U' %t
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; RUN: not grep "^BB.tomerge" %t
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; RUN: grep "^BB.nomerge" %t | count 4
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;
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; ModuleID = '<stdin>'
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declare i1 @foo()
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declare i1 @bar(i32)
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define i32 @test(i1 %a) {
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Q:
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br i1 %a, label %N, label %M
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N: ; preds = %Q
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br label %M
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M: ; preds = %N, %Q
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; It's ok to merge N and M because the incoming values for W are the
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; same for both cases...
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%W = phi i32 [ 2, %N ], [ 2, %Q ] ; <i32> [#uses=1]
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%R = add i32 %W, 1 ; <i32> [#uses=1]
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ret i32 %R
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}
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; Test merging of blocks with phi nodes where at least one incoming value
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; in the successor is undef.
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define i8 @testundef(i32 %u) {
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R:
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switch i32 %u, label %U [
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i32 0, label %S
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i32 1, label %T
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i32 2, label %T
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]
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S: ; preds = %R
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br label %U
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T: ; preds = %R, %R
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br label %U
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U: ; preds = %T, %S, %R
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; We should be able to merge either the S or T block into U by rewriting
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; R's incoming value with the incoming value of that predecessor since
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; R's incoming value is undef and both of those predecessors are simple
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; unconditional branches.
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%val.0 = phi i8 [ undef, %R ], [ 1, %T ], [ 0, %S ]
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ret i8 %val.0
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}
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; Test merging of blocks with phi nodes where at least one incoming value
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; in the successor is undef.
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define i8 @testundef2(i32 %u, i32* %A) {
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V:
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switch i32 %u, label %U [
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i32 0, label %W
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i32 1, label %X
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i32 2, label %X
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i32 3, label %Z
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]
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W: ; preds = %V
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br label %U
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Z:
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store i32 0, i32* %A, align 4
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br label %X
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X: ; preds = %V, %V, %Z
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br label %U
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U: ; preds = %X, %W, %V
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; We should be able to merge either the W or X block into U by rewriting
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; V's incoming value with the incoming value of that predecessor since
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; V's incoming value is undef and both of those predecessors are simple
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; unconditional branches. Note that X has predecessors beyond
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; the direct predecessors of U.
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%val.0 = phi i8 [ undef, %V ], [ 1, %X ], [ 1, %W ]
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ret i8 %val.0
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}
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define i8 @testmergesome(i32 %u, i32* %A) {
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V:
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switch i32 %u, label %Y [
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i32 0, label %W
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i32 1, label %X
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i32 2, label %X
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i32 3, label %Z
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]
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W: ; preds = %V
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store i32 1, i32* %A, align 4
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br label %Y
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Z:
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store i32 0, i32* %A, align 4
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br label %X
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X: ; preds = %V, %Z
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br label %Y
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Y: ; preds = %X, %W, %V
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; After merging X into Y, we should have 5 predecessors
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; and thus 5 incoming values to the phi.
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%val.0 = phi i8 [ 1, %V ], [ 1, %X ], [ 2, %W ]
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ret i8 %val.0
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}
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define i8 @testmergesome2(i32 %u, i32* %A) {
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V:
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switch i32 %u, label %W [
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i32 0, label %W
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i32 1, label %Y
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i32 2, label %X
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i32 4, label %Y
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]
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W: ; preds = %V
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store i32 1, i32* %A, align 4
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br label %Y
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X: ; preds = %V, %Z
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br label %Y
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Y: ; preds = %X, %W, %V
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; Ensure that we deal with both undef inputs for V when we merge in X.
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%val.0 = phi i8 [ undef, %V ], [ 1, %X ], [ 2, %W ], [ undef, %V ]
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ret i8 %val.0
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}
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; This function can't be merged
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define void @a() {
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entry:
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br label %BB.nomerge
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BB.nomerge: ; preds = %Common, %entry
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; This phi has a conflicting value (0) with below phi (2), so blocks
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; can't be merged.
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%a = phi i32 [ 1, %entry ], [ 0, %Common ] ; <i32> [#uses=1]
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br label %Succ
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Succ: ; preds = %Common, %BB.nomerge
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%b = phi i32 [ %a, %BB.nomerge ], [ 2, %Common ] ; <i32> [#uses=0]
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%conde = call i1 @foo( ) ; <i1> [#uses=1]
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br i1 %conde, label %Common, label %Exit
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Common: ; preds = %Succ
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%cond = call i1 @foo( ) ; <i1> [#uses=1]
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br i1 %cond, label %BB.nomerge, label %Succ
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Exit: ; preds = %Succ
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ret void
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}
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; This function can't be merged
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define void @b() {
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entry:
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br label %BB.nomerge
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BB.nomerge: ; preds = %Common, %entry
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br label %Succ
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Succ: ; preds = %Common, %BB.nomerge
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; This phi has confliction values for Common and (through BB) Common,
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; blocks can't be merged
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%b = phi i32 [ 1, %BB.nomerge ], [ 2, %Common ] ; <i32> [#uses=0]
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%conde = call i1 @foo( ) ; <i1> [#uses=1]
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br i1 %conde, label %Common, label %Exit
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Common: ; preds = %Succ
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%cond = call i1 @foo( ) ; <i1> [#uses=1]
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br i1 %cond, label %BB.nomerge, label %Succ
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Exit: ; preds = %Succ
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ret void
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}
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; This function can't be merged (for keeping canonical loop structures)
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define void @c() {
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entry:
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br label %BB.nomerge
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BB.nomerge: ; preds = %Common, %entry
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br label %Succ
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Succ: ; preds = %Common, %BB.tomerge, %Pre-Exit
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; This phi has identical values for Common and (through BB) Common,
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; blocks can't be merged
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%b = phi i32 [ 1, %BB.nomerge ], [ 1, %Common ], [ 2, %Pre-Exit ]
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%conde = call i1 @foo( ) ; <i1> [#uses=1]
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br i1 %conde, label %Common, label %Pre-Exit
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Common: ; preds = %Succ
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%cond = call i1 @foo( ) ; <i1> [#uses=1]
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br i1 %cond, label %BB.nomerge, label %Succ
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Pre-Exit: ; preds = %Succ
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; This adds a backedge, so the %b phi node gets a third branch and is
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; not completely trivial
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%cond2 = call i1 @foo( ) ; <i1> [#uses=1]
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br i1 %cond2, label %Succ, label %Exit
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Exit: ; preds = %Pre-Exit
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ret void
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}
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; This function can't be merged (for keeping canonical loop structures)
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define void @d() {
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entry:
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br label %BB.nomerge
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BB.nomerge: ; preds = %Common, %entry
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; This phi has a matching value (0) with below phi (0), so blocks
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; can be merged.
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%a = phi i32 [ 1, %entry ], [ 0, %Common ] ; <i32> [#uses=1]
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br label %Succ
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Succ: ; preds = %Common, %BB.tomerge
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%b = phi i32 [ %a, %BB.nomerge ], [ 0, %Common ] ; <i32> [#uses=0]
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%conde = call i1 @foo( ) ; <i1> [#uses=1]
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br i1 %conde, label %Common, label %Exit
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Common: ; preds = %Succ
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%cond = call i1 @foo( ) ; <i1> [#uses=1]
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br i1 %cond, label %BB.nomerge, label %Succ
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Exit: ; preds = %Succ
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ret void
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}
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; This function can be merged
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define void @e() {
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entry:
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br label %Succ
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Succ: ; preds = %Use, %entry
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; This phi is used somewhere else than Succ, but this should not prevent
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; merging this block
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%a = phi i32 [ 1, %entry ], [ 0, %Use ] ; <i32> [#uses=1]
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br label %BB.tomerge
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BB.tomerge: ; preds = %Succ
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%conde = call i1 @foo( ) ; <i1> [#uses=1]
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br i1 %conde, label %Use, label %Exit
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Use: ; preds = %Succ
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%cond = call i1 @bar( i32 %a ) ; <i1> [#uses=1]
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br i1 %cond, label %Succ, label %Exit
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Exit: ; preds = %Use, %Succ
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ret void
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}
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