[llvm] r324208 - [SimplifyCFG] Relax restriction for folding unconditional branches
Serguei Katkov via llvm-commits
llvm-commits at lists.llvm.org
Sun Feb 4 23:56:44 PST 2018
Author: skatkov
Date: Sun Feb 4 23:56:43 2018
New Revision: 324208
URL: http://llvm.org/viewvc/llvm-project?rev=324208&view=rev
Log:
[SimplifyCFG] Relax restriction for folding unconditional branches
The commit rL308422 introduces a restriction for folding unconditional
branches. Specifically if empty block with unconditional branch leads to
header of the loop then elimination of this basic block is prohibited.
However it seems this condition is redundantly strict.
If elimination of this basic block does not introduce more back edges
then we can eliminate this block.
The patch implements this relax of restriction.
Reviewers: efriedma, mcrosier, pacxx, hsung, davidxl
Reviewed By: pacxx
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D42691
Added:
llvm/trunk/test/Transforms/SimplifyCFG/UncondBranchToHeader.ll
Modified:
llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
llvm/trunk/test/Transforms/LoopUnroll/peel-loop.ll
llvm/trunk/test/Transforms/LoopUnswitch/2015-06-17-Metadata.ll
llvm/trunk/test/Transforms/LoopUnswitch/infinite-loop.ll
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=324208&r1=324207&r2=324208&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Sun Feb 4 23:56:43 2018
@@ -5733,9 +5733,12 @@ bool SimplifyCFGOpt::SimplifyUncondBranc
// header. (This is for early invocations before loop simplify and
// vectorization to keep canonical loop forms for nested loops. These blocks
// can be eliminated when the pass is invoked later in the back-end.)
+ // Note that if BB has only one predecessor then we do not introduce new
+ // backedge, so we can eliminate BB.
bool NeedCanonicalLoop =
Options.NeedCanonicalLoop &&
- (LoopHeaders && (LoopHeaders->count(BB) || LoopHeaders->count(Succ)));
+ (LoopHeaders && !BB->getSinglePredecessor() &&
+ (LoopHeaders->count(BB) || LoopHeaders->count(Succ)));
BasicBlock::iterator I = BB->getFirstNonPHIOrDbg()->getIterator();
if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
!NeedCanonicalLoop && TryToSimplifyUncondBranchFromEmptyBlock(BB))
Modified: llvm/trunk/test/Transforms/LoopUnroll/peel-loop.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/peel-loop.ll?rev=324208&r1=324207&r2=324208&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopUnroll/peel-loop.ll (original)
+++ llvm/trunk/test/Transforms/LoopUnroll/peel-loop.ll Sun Feb 4 23:56:43 2018
@@ -19,10 +19,8 @@
; CHECK: store i32 2, i32* %[[INC2]], align 4
; CHECK: %[[CMP3:.*]] = icmp eq i32 %k, 3
; CHECK: br i1 %[[CMP3]], label %for.end, label %[[LOOP_PH:.*]]
-; CHECK: [[LOOP_PH]]:
-; CHECK: br label %[[LOOP:.*]]
-; CHECK: [[LOOP]]:
-; CHECK: %[[IV:.*]] = phi i32 [ 3, %[[LOOP_PH]] ], [ {{.*}}, %[[LOOP]] ]
+; CHECK: for.end:
+; CHECK: ret void
define void @basic(i32* %p, i32 %k) #0 {
entry:
@@ -68,11 +66,8 @@ for.end:
; CHECK: store i32 2, i32* %[[INC2]], align 4
; CHECK: %[[CMP3:.*]] = icmp eq i32 %k, 3
; CHECK: br i1 %[[CMP3]], label %for.end, label %[[LOOP_PH:.*]]
-; CHECK: [[LOOP_PH]]:
-; CHECK: br label %[[LOOP:.*]]
-; CHECK: [[LOOP]]:
-; CHECK: %[[IV:.*]] = phi i32 [ 3, %[[LOOP_PH]] ], [ %[[IV:.*]], %[[LOOP]] ]
-; CHECK: %ret = phi i32 [ 0, %entry ], [ 1, %[[NEXT0]] ], [ 2, %[[NEXT1]] ], [ 3, %[[NEXT2]] ], [ %[[IV]], %[[LOOP]] ]
+; CHECK: for.end:
+; CHECK: %ret = phi i32 [ 0, %entry ], [ 1, %[[NEXT0]] ], [ 2, %[[NEXT1]] ], [ 3, %[[NEXT2]] ], [ %inc, %for.body ]
; CHECK: ret i32 %ret
define i32 @output(i32* %p, i32 %k) #0 {
entry:
Modified: llvm/trunk/test/Transforms/LoopUnswitch/2015-06-17-Metadata.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnswitch/2015-06-17-Metadata.ll?rev=324208&r1=324207&r2=324208&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopUnswitch/2015-06-17-Metadata.ll (original)
+++ llvm/trunk/test/Transforms/LoopUnswitch/2015-06-17-Metadata.ll Sun Feb 4 23:56:43 2018
@@ -16,7 +16,7 @@ for.body:
%cmp1 = icmp eq i32 %a, 12345
br i1 %cmp1, label %if.then, label %if.else, !prof !0
; CHECK: %cmp1 = icmp eq i32 %a, 12345
-; CHECK-NEXT: br i1 %cmp1, label %for.body.preheader.split.us, label %for.body.preheader.split, !prof !0
+; CHECK-NEXT: br i1 %cmp1, label %for.body.us, label %for.body, !prof !0
if.then: ; preds = %for.body
; CHECK: for.body.us:
; CHECK: add nsw i32 %{{.*}}, 123
@@ -53,7 +53,7 @@ entry:
br label %for.body
;CHECK: entry:
;CHECK-NEXT: %cmp1 = icmp eq i32 1, 2
-;CHECK-NEXT: br i1 %cmp1, label %entry.split, label %for.cond.cleanup.split, !prof !1
+;CHECK-NEXT: br i1 %cmp1, label %for.body, label %for.cond.cleanup.split, !prof !1
;CHECK: for.body:
for.body: ; preds = %for.inc, %entry
%inc.i = phi i32 [ 0, %entry ], [ %inc, %if.then ]
Modified: llvm/trunk/test/Transforms/LoopUnswitch/infinite-loop.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnswitch/infinite-loop.ll?rev=324208&r1=324207&r2=324208&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopUnswitch/infinite-loop.ll (original)
+++ llvm/trunk/test/Transforms/LoopUnswitch/infinite-loop.ll Sun Feb 4 23:56:43 2018
@@ -16,7 +16,7 @@
; CHECK-NEXT: br i1 %a, label %entry.split, label %abort0.split
; CHECK: entry.split:
-; CHECK-NEXT: br i1 %b, label %entry.split.split, label %abort1.split
+; CHECK-NEXT: br i1 %b, label %for.body, label %abort1.split
; CHECK: for.body:
; CHECK-NEXT: br label %for.body
Added: llvm/trunk/test/Transforms/SimplifyCFG/UncondBranchToHeader.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/UncondBranchToHeader.ll?rev=324208&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/UncondBranchToHeader.ll (added)
+++ llvm/trunk/test/Transforms/SimplifyCFG/UncondBranchToHeader.ll Sun Feb 4 23:56:43 2018
@@ -0,0 +1,18 @@
+; RUN: opt < %s -simplifycfg -S | FileCheck %s
+
+; Check that we can get rid of empty block leading to header
+; if it does not introduce new edge.
+define i32 @test(i32 %c) {
+entry:
+ br label %header
+header:
+ %i = phi i32 [0, %entry], [%i.1, %backedge]
+ %i.1 = add i32 %i, 1
+ %cmp = icmp slt i32 %i.1, %c
+ br i1 %cmp, label %backedge, label %exit
+; CHECK-NOT: backedge:
+backedge:
+ br label %header
+exit:
+ ret i32 %i
+}
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