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Fix a bug in IfConverter with nested predicates.
Prior to this patch, IfConverter may widen the cases where a sequence of instructions were executed because of the way it uses nested predicates. This result in incorrect execution. For instance, Let A be a basic block that flows conditionally into B and B be a predicated block. B can be predicated with A.BrToBPredicate into A iff B.Predicate is less "permissive" than A.BrToBPredicate, i.e., iff A.BrToBPredicate subsumes B.Predicate. The IfConverter was checking the opposite: B.Predicate subsumes A.BrToBPredicate. <rdar://problem/14379453> git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187071 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -720,9 +720,9 @@ bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
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if (BBI.IsDone || BBI.IsUnpredicable)
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return false;
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// If it is already predicated, check if its predicate subsumes the new
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// predicate.
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if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
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// If it is already predicated, check if the new predicate subsumes
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// its predicate.
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if (BBI.Predicate.size() && !TII->SubsumesPredicate(Pred, BBI.Predicate))
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return false;
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if (BBI.BrCond.size()) {
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@ -69,3 +69,62 @@ bb6.i350: ; preds = %bb2.i
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KBBlockZero.exit: ; preds = %bb2.i
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indirectbr i8* undef, [label %KBBlockZero_return_1, label %KBBlockZero_return_0]
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}
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; If-converter was checking for the wrong predicate subsumes pattern when doing
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; nested predicates.
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; E.g., Let A be a basic block that flows conditionally into B and B be a
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; predicated block.
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; B can be predicated with A.BrToBPredicate into A iff B.Predicate is less
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; "permissive" than A.BrToBPredicate, i.e., iff A.BrToBPredicate subsumes
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; B.Predicate.
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; <rdar://problem/14379453>
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; Hard-coded registers comes from the ABI.
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; CHECK: wrapDistance:
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; CHECK: cmp r1, #59
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; CHECK-NEXT: itt le
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; CHECK-NEXT: suble r0, r2, #1
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; CHECK-NEXT: bxle lr
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; CHECK-NEXT: subs [[REG:r[0-9]+]], #120
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; CHECK-NEXT: cmp [[REG]], r1
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; CHECK-NOT: it lt
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; CHECK-NEXT: bge [[LABEL:.+]]
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; Next BB
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; CHECK-NOT: cmplt
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; CHECK: cmp r0, #119
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; CHECK-NEXT: itt le
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; CHECK-NEXT: addle r0, r1, #1
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; CHECK-NEXT: bxle lr
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; Next BB
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; CHECK: [[LABEL]]:
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; CHECK-NEXT: subs r0, r1, r0
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; CHECK-NEXT: bx lr
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define i32 @wrapDistance(i32 %tx, i32 %sx, i32 %w) {
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entry:
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%cmp = icmp slt i32 %sx, 60
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br i1 %cmp, label %if.then, label %if.else
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if.then: ; preds = %entry
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%sub = add nsw i32 %w, -1
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br label %return
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if.else: ; preds = %entry
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%sub1 = add nsw i32 %w, -120
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%cmp2 = icmp slt i32 %sub1, %sx
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%cmp3 = icmp slt i32 %tx, 120
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%or.cond = and i1 %cmp2, %cmp3
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br i1 %or.cond, label %if.then4, label %if.end5
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if.then4: ; preds = %if.else
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%add = add nsw i32 %sx, 1
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br label %return
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if.end5: ; preds = %if.else
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%sub6 = sub nsw i32 %sx, %tx
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br label %return
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return: ; preds = %if.end5, %if.then4, %if.then
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%retval.0 = phi i32 [ %sub, %if.then ], [ %add, %if.then4 ], [ %sub6, %if.end5 ]
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ret i32 %retval.0
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}
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