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Generalize GVN's conditional propagation logic slightly:

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it's OK for the false/true destination to have multiple
predecessors as long as the extra ones are dominated by
the branch destination.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141176 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2011-10-05 14:17:01 +00:00
parent 4cbc5a1118
commit 452c58f4c4
2 changed files with 50 additions and 5 deletions
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33
lib/Transforms/Scalar/GVN.cpp
View File

@ -1921,14 +1921,39 @@ bool GVN::processInstruction(Instruction *I) {
BasicBlock *TrueSucc = BI->getSuccessor(0);
BasicBlock *FalseSucc = BI->getSuccessor(1);
if (TrueSucc->getSinglePredecessor())
BasicBlock *Parent = BI->getParent();
// If the true and false branches are to the same basic block then the
// branch gives no information about the condition. Eliminating this
// here simplifies the rest of the logic.
if (TrueSucc == FalseSucc)
return false;
// If the true block can be reached without executing the true edge then we
// can't say anything about the value of the condition there.
for (pred_iterator PI = pred_begin(TrueSucc), PE = pred_end(TrueSucc);
PI != PE; ++PI)
if (*PI != Parent && !DT->dominates(TrueSucc, *PI)) {
TrueSucc = 0;
break;
}
// If the false block can be reached without executing the false edge then
// we can't say anything about the value of the condition there.
for (pred_iterator PI = pred_begin(FalseSucc), PE = pred_end(FalseSucc);
PI != PE; ++PI)
if (*PI != Parent && !DT->dominates(FalseSucc, *PI)) {
FalseSucc = 0;
break;
}
if (TrueSucc)
addToLeaderTable(CondVN,
ConstantInt::getTrue(TrueSucc->getContext()),
TrueSucc);
if (FalseSucc->getSinglePredecessor())
if (FalseSucc)
addToLeaderTable(CondVN,
ConstantInt::getFalse(TrueSucc->getContext()),
ConstantInt::getFalse(FalseSucc->getContext()),
FalseSucc);
return false;

22
test/Transforms/GVN/condprop.ll
View File

@ -52,4 +52,24 @@ bb8: ; preds = %bb7, %bb6, %bb4, %bb2, %bb
return: ; preds = %bb8
ret i32 %.0
}
}
declare void @ext(i1)
; CHECK: @bar
define void @bar(i1 %x, i1 %y) {
%z = or i1 %x, %y
br i1 %z, label %true, label %false
true:
; CHECK: true:
%z2 = or i1 %x, %y
call void @ext(i1 %z2)
; CHECK: call void @ext(i1 true)
br label %true
false:
; CHECK: false:
%z3 = or i1 %x, %y
call void @ext(i1 %z3)
; CHECK: call void @ext(i1 false)
br label %false
}