TryToSimplifyUncondBranchFromEmptyBlock was checking that any common

predecessors of the two blocks it is attempting to merge supply the
same incoming values to any phi in the successor block.  This change
allows merging in the case where there is one or more incoming values
that are undef.  The undef values are rewritten to match the non-undef
value that flows from the other edge.  Patch by Mark Lacey.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186069 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 239 insertions, 1 deletions

diff --git a/test/Transforms/SimplifyCFG/EqualPHIEdgeBlockMerge.ll b/test/Transforms/SimplifyCFG/EqualPHIEdgeBlockMerge.ll
index 912c755..b07ef97 100644
--- a/test/Transforms/SimplifyCFG/EqualPHIEdgeBlockMerge.ll
+++ b/test/Transforms/SimplifyCFG/EqualPHIEdgeBlockMerge.ll
@@ -1,8 +1,18 @@
 ; Test merging of blocks with phi nodes.
 ;
-; RUN: opt < %s -simplifycfg -S | not grep N:
+; RUN: opt < %s -simplifycfg -S > %t
+; RUN: not grep N: %t
+; RUN: not grep X: %t
+; RUN: not grep 'switch i32[^U]+%U' %t
+; RUN: not grep "^BB.tomerge" %t
+; RUN: grep "^BB.nomerge" %t | count 2
 ;
 
+; ModuleID = '<stdin>'
+declare i1 @foo()
+
+declare i1 @bar(i32)
+
 define i32 @test(i1 %a) {
 Q:
         br i1 %a, label %N, label %M
@@ -16,3 +26,231 @@ M:              ; preds = %N, %Q
         ret i32 %R
 }
 
+; Test merging of blocks with phi nodes where at least one incoming value
+; in the successor is undef.
+define i8 @testundef(i32 %u) {
+R:
+  switch i32 %u, label %U [
+    i32 0, label %S
+    i32 1, label %T
+    i32 2, label %T
+  ]
+
+S:                                            ; preds = %R
+  br label %U
+
+T:                                           ; preds = %R, %R
+  br label %U
+
+U:                                        ; preds = %T, %S, %R
+  ; We should be able to merge either the S or T block into U by rewriting
+  ; R's incoming value with the incoming value of that predecessor since
+  ; R's incoming value is undef and both of those predecessors are simple
+  ; unconditional branches.
+  %val.0 = phi i8 [ undef, %R ], [ 1, %T ], [ 0, %S ]
+  ret i8 %val.0
+}
+
+; Test merging of blocks with phi nodes where at least one incoming value
+; in the successor is undef.
+define i8 @testundef2(i32 %u, i32* %A) {
+V:
+  switch i32 %u, label %U [
+    i32 0, label %W
+    i32 1, label %X
+    i32 2, label %X
+    i32 3, label %Z
+  ]
+
+W:                                            ; preds = %V
+  br label %U
+
+Z:
+  store i32 0, i32* %A, align 4
+  br label %X
+
+X:                                           ; preds = %V, %V, %Z
+  br label %U
+
+U:                                        ; preds = %X, %W, %V
+  ; We should be able to merge either the W or X block into U by rewriting
+  ; V's incoming value with the incoming value of that predecessor since
+  ; V's incoming value is undef and both of those predecessors are simple
+  ; unconditional branches. Note that X has predecessors beyond
+  ; the direct predecessors of U.
+  %val.0 = phi i8 [ undef, %V ], [ 1, %X ], [ 1, %W ]
+  ret i8 %val.0
+}
+
+define i8 @testmergesome(i32 %u, i32* %A) {
+V:
+  switch i32 %u, label %Y [
+    i32 0, label %W
+    i32 1, label %X
+    i32 2, label %X
+    i32 3, label %Z
+  ]
+
+W:                                            ; preds = %V
+  store i32 1, i32* %A, align 4
+  br label %Y
+
+Z:
+  store i32 0, i32* %A, align 4
+  br label %X
+
+X:                                           ; preds = %V, %Z
+  br label %Y
+
+Y:                                        ; preds = %X, %W, %V
+  ; After merging X into Y, we should have 5 predecessors
+  ; and thus 5 incoming values to the phi.
+  %val.0 = phi i8 [ 1, %V ], [ 1, %X ], [ 2, %W ]
+  ret i8 %val.0
+}
+
+
+define i8 @testmergesome2(i32 %u, i32* %A) {
+V:
+  switch i32 %u, label %W [
+    i32 0, label %W
+    i32 1, label %Y
+    i32 2, label %X
+    i32 4, label %Y
+  ]
+
+W:                                            ; preds = %V
+  store i32 1, i32* %A, align 4
+  br label %Y
+
+X:                                           ; preds = %V, %Z
+  br label %Y
+
+Y:                                        ; preds = %X, %W, %V
+  ; Ensure that we deal with both undef inputs for V when we merge in X.
+  %val.0 = phi i8 [ undef, %V ], [ 1, %X ], [ 2, %W ], [ undef, %V ]
+  ret i8 %val.0
+}
+
+; This function can't be merged
+define void @a() {
+entry:
+	br label %BB.nomerge
+
+BB.nomerge:		; preds = %Common, %entry
+        ; This phi has a conflicting value (0) with below phi (2), so blocks
+        ; can't be merged.
+	%a = phi i32 [ 1, %entry ], [ 0, %Common ]		; <i32> [#uses=1]
+	br label %Succ
+
+Succ:		; preds = %Common, %BB.nomerge
+	%b = phi i32 [ %a, %BB.nomerge ], [ 2, %Common ]		; <i32> [#uses=0]
+	%conde = call i1 @foo( )		; <i1> [#uses=1]
+	br i1 %conde, label %Common, label %Exit
+
+Common:		; preds = %Succ
+	%cond = call i1 @foo( )		; <i1> [#uses=1]
+	br i1 %cond, label %BB.nomerge, label %Succ
+
+Exit:		; preds = %Succ
+	ret void
+}
+
+; This function can't be merged
+define void @b() {
+entry:
+	br label %BB.nomerge
+
+BB.nomerge:		; preds = %Common, %entry
+	br label %Succ
+
+Succ:		; preds = %Common, %BB.nomerge
+        ; This phi has confliction values for Common and (through BB) Common,
+        ; blocks can't be merged
+	%b = phi i32 [ 1, %BB.nomerge ], [ 2, %Common ]		; <i32> [#uses=0]
+	%conde = call i1 @foo( )		; <i1> [#uses=1]
+	br i1 %conde, label %Common, label %Exit
+
+Common:		; preds = %Succ
+	%cond = call i1 @foo( )		; <i1> [#uses=1]
+	br i1 %cond, label %BB.nomerge, label %Succ
+
+Exit:		; preds = %Succ
+	ret void
+}
+
+; This function can be merged
+define void @c() {
+entry:
+	br label %BB.tomerge
+
+BB.tomerge:		; preds = %Common, %entry
+	br label %Succ
+
+Succ:		; preds = %Common, %BB.tomerge, %Pre-Exit
+        ; This phi has identical values for Common and (through BB) Common,
+        ; blocks can't be merged
+	%b = phi i32 [ 1, %BB.tomerge ], [ 1, %Common ], [ 2, %Pre-Exit ]
+	%conde = call i1 @foo( )		; <i1> [#uses=1]
+	br i1 %conde, label %Common, label %Pre-Exit
+
+Common:		; preds = %Succ
+	%cond = call i1 @foo( )		; <i1> [#uses=1]
+	br i1 %cond, label %BB.tomerge, label %Succ
+
+Pre-Exit:       ; preds = %Succ
+        ; This adds a backedge, so the %b phi node gets a third branch and is
+        ; not completely trivial
+	%cond2 = call i1 @foo( )		; <i1> [#uses=1]
+	br i1 %cond2, label %Succ, label %Exit
+
+Exit:		; preds = %Pre-Exit
+	ret void
+}
+
+; This function can be merged
+define void @d() {
+entry:
+	br label %BB.tomerge
+
+BB.tomerge:		; preds = %Common, %entry
+        ; This phi has a matching value (0) with below phi (0), so blocks
+        ; can be merged.
+	%a = phi i32 [ 1, %entry ], [ 0, %Common ]		; <i32> [#uses=1]
+	br label %Succ
+
+Succ:		; preds = %Common, %BB.tomerge
+	%b = phi i32 [ %a, %BB.tomerge ], [ 0, %Common ]		; <i32> [#uses=0]
+	%conde = call i1 @foo( )		; <i1> [#uses=1]
+	br i1 %conde, label %Common, label %Exit
+
+Common:		; preds = %Succ
+	%cond = call i1 @foo( )		; <i1> [#uses=1]
+	br i1 %cond, label %BB.tomerge, label %Succ
+
+Exit:		; preds = %Succ
+	ret void
+}
+
+; This function can be merged
+define void @e() {
+entry:
+	br label %BB.tomerge
+
+BB.tomerge:		; preds = %Use, %entry
+        ; This phi is used somewhere else than Succ, but this should not prevent
+        ; merging this block
+	%a = phi i32 [ 1, %entry ], [ 0, %Use ]		; <i32> [#uses=1]
+	br label %Succ
+
+Succ:		; preds = %BB.tomerge
+	%conde = call i1 @foo( )		; <i1> [#uses=1]
+	br i1 %conde, label %Use, label %Exit
+
+Use:		; preds = %Succ
+	%cond = call i1 @bar( i32 %a )		; <i1> [#uses=1]
+	br i1 %cond, label %BB.tomerge, label %Exit
+
+Exit:		; preds = %Use, %Succ
+	ret void
+}