forked from OSchip/llvm-project
[SimplifyCFG] Re-apply 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. The test profile/Linux/counter_promo_nest.c in compiler-rt project is updated to meet this change. Reviewers: efriedma, mcrosier, pacxx, hsung, davidxl Reviewed By: pacxx Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D42691 llvm-svn: 324572
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parent
d535c4d9d2
commit
66182d6c38
llvm
lib/Transforms/Utils
test/Transforms
LoopUnroll
LoopUnswitch
SimplifyCFG
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@ -5733,9 +5733,12 @@ bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI,
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// header. (This is for early invocations before loop simplify and
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// vectorization to keep canonical loop forms for nested loops. These blocks
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// can be eliminated when the pass is invoked later in the back-end.)
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// Note that if BB has only one predecessor then we do not introduce new
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// backedge, so we can eliminate BB.
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bool NeedCanonicalLoop =
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Options.NeedCanonicalLoop &&
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(LoopHeaders && (LoopHeaders->count(BB) || LoopHeaders->count(Succ)));
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(LoopHeaders && std::distance(pred_begin(BB), pred_end(BB)) > 1 &&
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(LoopHeaders->count(BB) || LoopHeaders->count(Succ)));
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BasicBlock::iterator I = BB->getFirstNonPHIOrDbg()->getIterator();
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if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
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!NeedCanonicalLoop && TryToSimplifyUncondBranchFromEmptyBlock(BB))
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@ -19,10 +19,8 @@
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; CHECK: store i32 2, i32* %[[INC2]], align 4
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; CHECK: %[[CMP3:.*]] = icmp eq i32 %k, 3
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; CHECK: br i1 %[[CMP3]], label %for.end, label %[[LOOP_PH:.*]]
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; CHECK: [[LOOP_PH]]:
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; CHECK: br label %[[LOOP:.*]]
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; CHECK: [[LOOP]]:
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; CHECK: %[[IV:.*]] = phi i32 [ 3, %[[LOOP_PH]] ], [ {{.*}}, %[[LOOP]] ]
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; CHECK: for.end:
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; CHECK: ret void
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define void @basic(i32* %p, i32 %k) #0 {
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entry:
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@ -68,11 +66,8 @@ for.end: ; preds = %for.cond.for.end_cr
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; CHECK: store i32 2, i32* %[[INC2]], align 4
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; CHECK: %[[CMP3:.*]] = icmp eq i32 %k, 3
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; CHECK: br i1 %[[CMP3]], label %for.end, label %[[LOOP_PH:.*]]
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; CHECK: [[LOOP_PH]]:
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; CHECK: br label %[[LOOP:.*]]
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; CHECK: [[LOOP]]:
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; CHECK: %[[IV:.*]] = phi i32 [ 3, %[[LOOP_PH]] ], [ %[[IV:.*]], %[[LOOP]] ]
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; CHECK: %ret = phi i32 [ 0, %entry ], [ 1, %[[NEXT0]] ], [ 2, %[[NEXT1]] ], [ 3, %[[NEXT2]] ], [ %[[IV]], %[[LOOP]] ]
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; CHECK: for.end:
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; CHECK: %ret = phi i32 [ 0, %entry ], [ 1, %[[NEXT0]] ], [ 2, %[[NEXT1]] ], [ 3, %[[NEXT2]] ], [ %inc, %for.body ]
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; CHECK: ret i32 %ret
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define i32 @output(i32* %p, i32 %k) #0 {
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entry:
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@ -16,7 +16,7 @@ for.body: ; preds = %for.inc, %for.body.
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%cmp1 = icmp eq i32 %a, 12345
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br i1 %cmp1, label %if.then, label %if.else, !prof !0
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; CHECK: %cmp1 = icmp eq i32 %a, 12345
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; CHECK-NEXT: br i1 %cmp1, label %for.body.preheader.split.us, label %for.body.preheader.split, !prof !0
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; CHECK-NEXT: br i1 %cmp1, label %for.body.us, label %for.body, !prof !0
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if.then: ; preds = %for.body
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; CHECK: for.body.us:
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; CHECK: add nsw i32 %{{.*}}, 123
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@ -53,7 +53,7 @@ entry:
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br label %for.body
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;CHECK: entry:
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;CHECK-NEXT: %cmp1 = icmp eq i32 1, 2
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;CHECK-NEXT: br i1 %cmp1, label %entry.split, label %for.cond.cleanup.split, !prof !1
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;CHECK-NEXT: br i1 %cmp1, label %for.body, label %for.cond.cleanup.split, !prof !1
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;CHECK: for.body:
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for.body: ; preds = %for.inc, %entry
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%inc.i = phi i32 [ 0, %entry ], [ %inc, %if.then ]
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@ -16,7 +16,7 @@
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; CHECK-NEXT: br i1 %a, label %entry.split, label %abort0.split
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; CHECK: entry.split:
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; CHECK-NEXT: br i1 %b, label %entry.split.split, label %abort1.split
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; CHECK-NEXT: br i1 %b, label %for.body, label %abort1.split
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; CHECK: for.body:
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; CHECK-NEXT: br label %for.body
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@ -0,0 +1,18 @@
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; RUN: opt < %s -simplifycfg -S | FileCheck %s
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; Check that we can get rid of empty block leading to header
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; if it does not introduce new edge.
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define i32 @test(i32 %c) {
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entry:
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br label %header
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header:
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%i = phi i32 [0, %entry], [%i.1, %backedge]
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%i.1 = add i32 %i, 1
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%cmp = icmp slt i32 %i.1, %c
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br i1 %cmp, label %backedge, label %exit
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; CHECK-NOT: backedge:
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backedge:
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br label %header
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exit:
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ret i32 %i
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}
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