[PATCH] D30455: [InstCombine] Avoid faulty combines of select-cmp-br
Bjorn Pettersson via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Thu Mar 2 01:52:14 PST 2017
bjope updated this revision to Diff 90301.
bjope added a comment.
Updated the test case (as suggested by spatel).
- Rebased to later revision on trunc
- Removed the irrelevant add from test6
- Generated names using opt --instnamer
- Generated checks using utils/update_test_checks.py
https://reviews.llvm.org/D30455
Files:
lib/Transforms/InstCombine/InstCombineCompares.cpp
test/Transforms/InstCombine/select-cmp-br.ll
Index: test/Transforms/InstCombine/select-cmp-br.ll
===================================================================
--- test/Transforms/InstCombine/select-cmp-br.ll
+++ test/Transforms/InstCombine/select-cmp-br.ll
@@ -242,3 +242,22 @@
br label %bb
}
+; Negative test. Must not trigger the select-cmp-br combine because the result
+; of the select is used in both flows following the br (the special case where
+; the conditional branch has the same target for both flows).
+define i32 @test6(i32 %arg, i1 %arg1) {
+; CHECK-LABEL: @test6(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 undef, label [[BB:%.*]], label [[BB]]
+; CHECK: bb:
+; CHECK-NEXT: [[TMP:%.*]] = select i1 [[ARG1:%.*]], i32 [[ARG:%.*]], i32 0
+; CHECK-NEXT: ret i32 [[TMP]]
+;
+entry:
+ %tmp = select i1 %arg1, i32 %arg, i32 0
+ %tmp2 = icmp eq i32 %tmp, 0
+ br i1 %tmp2, label %bb, label %bb
+
+bb: ; preds = %entry, %entry
+ ret i32 %tmp
+}
Index: lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3950,16 +3950,18 @@
assert((SIOpd == 1 || SIOpd == 2) && "Invalid select operand!");
if (isChainSelectCmpBranch(SI) && Icmp->getPredicate() == ICmpInst::ICMP_EQ) {
BasicBlock *Succ = SI->getParent()->getTerminator()->getSuccessor(1);
- // The check for the unique predecessor is not the best that can be
+ // The check for the single predecessor is not the best that can be
// done. But it protects efficiently against cases like when SI's
// home block has two successors, Succ and Succ1, and Succ1 predecessor
// of Succ. Then SI can't be replaced by SIOpd because the use that gets
// replaced can be reached on either path. So the uniqueness check
// guarantees that the path all uses of SI (outside SI's parent) are on
// is disjoint from all other paths out of SI. But that information
// is more expensive to compute, and the trade-off here is in favor
- // of compile-time.
- if (Succ->getUniquePredecessor() && dominatesAllUses(SI, Icmp, Succ)) {
+ // of compile-time. It should also be noticed that we check for a single
+ // predecessor and not only uniqueness. This to handle the situation when
+ // Succ and Succ1 points to the same basic block.
+ if (Succ->getSinglePredecessor() && dominatesAllUses(SI, Icmp, Succ)) {
NumSel++;
SI->replaceUsesOutsideBlock(SI->getOperand(SIOpd), SI->getParent());
return true;
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