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Make jump threading eliminate blocks that just contain phi nodes,

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debug intrinsics, and an unconditional branch when possible.  This
reuses the TryToSimplifyUncondBranchFromEmptyBlock function split
out of simplifycfg.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86722 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-11-10 21:40:01 +00:00
parent 81ebdcf7dd
commit f3183f6da6
2 changed files with 34 additions and 3 deletions
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21
lib/Transforms/Scalar/JumpThreading.cpp
View File

@ -115,6 +115,7 @@ bool JumpThreading::runOnFunction(Function &F) {
bool Changed = false;
for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
BasicBlock *BB = I;
// Thread all of the branches we can over this block.
while (ProcessBlock(BB))
Changed = true;
@ -129,6 +130,26 @@ bool JumpThreading::runOnFunction(Function &F) {
LoopHeaders.erase(BB);
DeleteDeadBlock(BB);
Changed = true;
} else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
// Can't thread an unconditional jump, but if the block is "almost
// empty", we can replace uses of it with uses of the successor and make
// this dead.
if (BI->isUnconditional() &&
BB != &BB->getParent()->getEntryBlock()) {
BasicBlock::iterator BBI = BB->getFirstNonPHI();
// Ignore dbg intrinsics.
while (isa<DbgInfoIntrinsic>(BBI))
++BBI;
// If the terminator is the only non-phi instruction, try to nuke it.
if (BBI->isTerminator()) {
bool Erased = LoopHeaders.erase(BB);
if (TryToSimplifyUncondBranchFromEmptyBlock(BB))
Changed = true;
else if (Erased)
LoopHeaders.insert(BB);
}
}
}
}
AnotherIteration = Changed;

16
test/Transforms/JumpThreading/basic.ll
View File

@ -211,19 +211,29 @@ define i32 @test8b(i1 %cond, i1 %cond2) {
T0:
%A = call i1 @test8a()
br i1 %A, label %T1, label %F1
; CHECK: T0:
; CHECK-NEXT: call
; CHECK-NEXT: br i1 %A, label %T1, label %Y
T1:
%B = call i1 @test8a()
br i1 %B, label %T2, label %F1
; CHECK: T1:
; CHECK-NEXT: call
; CHECK-NEXT: br i1 %B, label %T2, label %Y
T2:
%C = call i1 @test8a()
br i1 %cond, label %T3, label %F1
; CHECK: T2:
; CHECK-NEXT: call
; CHECK-NEXT: br i1 %cond, label %T3, label %Y
T3:
ret i32 0
F1:
; TODO: F1 uncond branch block should be removed, T2 should jump directly to Y.
; CHECK: F1:
; CHECK-NEXT br label %Y
%D = phi i32 [0, %T0], [0, %T1], [1, %T2]
%E = icmp eq i32 %D, 1
%F = and i1 %E, %cond