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Index: test/Transforms/JumpThreading/header-succ.ll
===================================================================
--- a/test/Transforms/JumpThreading/header-succ.ll
+++ b/test/Transforms/JumpThreading/header-succ.ll
@@ -0,0 +1,99 @@
+; RUN: opt -S -jump-threading < %s | FileCheck %s
+
+; Check that the heuristic for avoiding accidental introduction of irreducible
+; loops doesn't also prevent us from threading simple constructs where this
+; isn't a problem.
+
+declare void @opaque_body()
+
+define void @jump_threading_loopheader() {
+; CHECK-LABEL: @jump_threading_loopheader
+top:
+ br label %entry
+
+entry:
+ %ind = phi i32 [0, %top], [%nextind, %latch]
+ %nextind = add i32 %ind, 1
+ %cmp = icmp ule i32 %ind, 10
+; CHECK: br i1 %cmp, label %latch, label %exit
+ br i1 %cmp, label %body, label %latch
+
+body:
+ call void @opaque_body()
+; CHECK: br label %entry
+ br label %latch
+
+latch:
+ %cond = phi i2 [1, %entry], [2, %body]
+ switch i2 %cond, label %unreach [
+ i2 2, label %entry
+ i2 1, label %exit
+ ]
+
+unreach:
+ unreachable
+
+exit:
+ ret void
+}
+
+; We also need to check the opposite order of the branches, in the switch
+; instruction because jump-threading relies on that to decide which edge to
+; try to thread first.
+define void @jump_threading_loopheader2() {
+; CHECK-LABEL: @jump_threading_loopheader2
+top:
+ br label %entry
+
+entry:
+ %ind = phi i32 [0, %top], [%nextind, %latch]
+ %nextind = add i32 %ind, 1
+ %cmp = icmp ule i32 %ind, 10
+; CHECK: br i1 %cmp, label %exit, label %latch
+ br i1 %cmp, label %body, label %latch
+
+body:
+ call void @opaque_body()
+; CHECK: br label %entry
+ br label %latch
+
+latch:
+ %cond = phi i2 [1, %entry], [2, %body]
+ switch i2 %cond, label %unreach [
+ i2 1, label %entry
+ i2 2, label %exit
+ ]
+
+unreach:
+ unreachable
+
+exit:
+ ret void
+}
+
+; Check if we can handle undef branch condition.
+define void @jump_threading_loopheader3() {
+; CHECK-LABEL: @jump_threading_loopheader3
+top:
+ br label %entry
+
+entry:
+ %ind = phi i32 [0, %top], [%nextind, %latch]
+ %nextind = add i32 %ind, 1
+ %cmp = icmp ule i32 %ind, 10
+; CHECK: br i1 %cmp, label %latch, label %exit
+ br i1 %cmp, label %body, label %latch
+
+body:
+ call void @opaque_body()
+; CHECK: br label %entry
+ br label %latch
+
+latch:
+ %phi = phi i32 [undef, %entry], [0, %body]
+ %cmp1 = icmp eq i32 %phi, 0
+ br i1 %cmp1, label %entry, label %exit
+
+exit:
+ ret void
+}
Index: lib/Transforms/Scalar/JumpThreading.cpp
===================================================================
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1499,6 +1499,9 @@
if (PredToDest.second)
DestPopularity[PredToDest.second]++;
+ if (DestPopularity.empty())
+ return nullptr;
+
// Find the most popular dest.
DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin();
BasicBlock *MostPopularDest = DPI->first;
@@ -1679,8 +1682,20 @@
// threadable destination (the common case) we can avoid this.
BasicBlock *MostPopularDest = OnlyDest;
- if (MostPopularDest == MultipleDestSentinel)
+ if (MostPopularDest == MultipleDestSentinel) {
+ // Remove any loop headers from the Dest list, ThreadEdge conservatively
+ // won't process them, but we might have other destination that are eligible
+ // and we still want to process.
+ erase_if(PredToDestList,
+ [&](const std::pair<BasicBlock *, BasicBlock *> &PredToDest) {
+ return LoopHeaders.count(PredToDest.second) != 0;
+ });
+
+ if (PredToDestList.empty())
+ return false;
+
MostPopularDest = FindMostPopularDest(BB, PredToDestList);
+ }
// Now that we know what the most popular destination is, factor all
// predecessors that will jump to it into a single predecessor.
|
