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Nick pointed out on IRC that GVN's propagateEquality wasn't propagating
equalities into phi node operands for which the equality is known to hold in the incoming basic block. That's because replaceAllDominatedUsesWith wasn't handling phi nodes correctly in general (that this didn't give wrong results was just luck: the specific way GVN uses replaceAllDominatedUsesWith precluded wrong changes to phi nodes). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152006 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -1953,7 +1953,17 @@ unsigned GVN::replaceAllDominatedUsesWith(Value *From, Value *To,
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for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
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UI != UE; ) {
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Use &U = (UI++).getUse();
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if (DT->dominates(Root, cast<Instruction>(U.getUser())->getParent())) {
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// If From occurs as a phi node operand then the use implicitly lives in the
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// corresponding incoming block. Otherwise it is the block containing the
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// user that must be dominated by Root.
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BasicBlock *UsingBlock;
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if (PHINode *PN = dyn_cast<PHINode>(U.getUser()))
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UsingBlock = PN->getIncomingBlock(U);
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else
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UsingBlock = cast<Instruction>(U.getUser())->getParent();
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if (DT->dominates(Root, UsingBlock)) {
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U.set(To);
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++Count;
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}
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@ -232,3 +232,20 @@ cond_true2:
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next2:
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ret i32 0
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}
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; CHECK: @test12
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define i32 @test12(i32 %x) {
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%cmp = icmp eq i32 %x, 0
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br i1 %cmp, label %cond_true, label %cond_false
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cond_true:
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br label %ret
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cond_false:
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br label %ret
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ret:
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%res = phi i32 [ %x, %cond_true ], [ %x, %cond_false ]
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; CHECK: %res = phi i32 [ 0, %cond_true ], [ %x, %cond_false ]
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ret i32 %res
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}
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