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make jump threading handle lexically identical compare instructions
as if they were multiple uses of the same instruction. This interacts well with the existing loadpre that j-t does to open up many new jump threads earlier. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73768 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -324,10 +324,6 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
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}
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}
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// If there is only a single predecessor of this block, nothing to fold.
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if (BB->getSinglePredecessor())
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return false;
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// All the rest of our checks depend on the condition being an instruction.
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if (CondInst == 0)
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return false;
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@ -358,6 +354,23 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
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if (ProcessBranchOnCompare(CondCmp, BB))
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return true;
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}
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// If we have a comparison, loop over the predecessors to see if there is
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// a condition with the same value.
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pred_iterator PI = pred_begin(BB), E = pred_end(BB);
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for (; PI != E; ++PI)
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if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
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if (PBI->isConditional() && *PI != BB) {
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if (CmpInst *CI = dyn_cast<CmpInst>(PBI->getCondition())) {
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if (CI->getOperand(0) == CondCmp->getOperand(0) &&
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CI->getOperand(1) == CondCmp->getOperand(1) &&
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CI->getPredicate() == CondCmp->getPredicate()) {
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// TODO: Could handle things like (x != 4) --> (x == 17)
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if (ProcessBranchOnDuplicateCond(*PI, BB))
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return true;
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}
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}
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}
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}
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// Check for some cases that are worth simplifying. Right now we want to look
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30
test/Transforms/JumpThreading/dup-cond.ll
Normal file
30
test/Transforms/JumpThreading/dup-cond.ll
Normal file
@ -0,0 +1,30 @@
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; RUN: llvm-as < %s | opt -jump-threading -die | llvm-dis | grep icmp | count 1
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declare void @f1()
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declare void @f2()
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declare void @f3()
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define i32 @test(i32 %A) {
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%tmp455 = icmp eq i32 %A, 42
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br i1 %tmp455, label %BB1, label %BB2
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BB2:
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call void @f1()
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br label %BB1
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BB1:
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%tmp459 = icmp eq i32 %A, 42
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br i1 %tmp459, label %BB3, label %BB4
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BB3:
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call void @f2()
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ret i32 3
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BB4:
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call void @f3()
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ret i32 4
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}
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