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Fix a bug in IfConverter with nested predicates.

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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
This commit is contained in:
Quentin Colombet 2013-07-24 20:20:37 +00:00
parent 6482427926
commit e644b7743b
2 changed files with 62 additions and 3 deletions
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6
lib/CodeGen/IfConversion.cpp
View File

@ -720,9 +720,9 @@ bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
if (BBI.IsDone || BBI.IsUnpredicable)
return false;
// If it is already predicated, check if its predicate subsumes the new
// predicate.
if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
// If it is already predicated, check if the new predicate subsumes
// its predicate.
if (BBI.Predicate.size() && !TII->SubsumesPredicate(Pred, BBI.Predicate))
return false;
if (BBI.BrCond.size()) {

59
test/CodeGen/ARM/2013-05-05-IfConvertBug.ll
View File

@ -69,3 +69,62 @@ bb6.i350: ; preds = %bb2.i
KBBlockZero.exit: ; preds = %bb2.i
indirectbr i8* undef, [label %KBBlockZero_return_1, label %KBBlockZero_return_0]
}
; If-converter was checking for the wrong predicate subsumes pattern when doing
; nested predicates.
; E.g., 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.
; <rdar://problem/14379453>
; Hard-coded registers comes from the ABI.
; CHECK: wrapDistance:
; CHECK: cmp r1, #59
; CHECK-NEXT: itt le
; CHECK-NEXT: suble r0, r2, #1
; CHECK-NEXT: bxle lr
; CHECK-NEXT: subs [[REG:r[0-9]+]], #120
; CHECK-NEXT: cmp [[REG]], r1
; CHECK-NOT: it lt
; CHECK-NEXT: bge [[LABEL:.+]]
; Next BB
; CHECK-NOT: cmplt
; CHECK: cmp r0, #119
; CHECK-NEXT: itt le
; CHECK-NEXT: addle r0, r1, #1
; CHECK-NEXT: bxle lr
; Next BB
; CHECK: [[LABEL]]:
; CHECK-NEXT: subs r0, r1, r0
; CHECK-NEXT: bx lr
define i32 @wrapDistance(i32 %tx, i32 %sx, i32 %w) {
entry:
%cmp = icmp slt i32 %sx, 60
br i1 %cmp, label %if.then, label %if.else
if.then: ; preds = %entry
%sub = add nsw i32 %w, -1
br label %return
if.else: ; preds = %entry
%sub1 = add nsw i32 %w, -120
%cmp2 = icmp slt i32 %sub1, %sx
%cmp3 = icmp slt i32 %tx, 120
%or.cond = and i1 %cmp2, %cmp3
br i1 %or.cond, label %if.then4, label %if.end5
if.then4: ; preds = %if.else
%add = add nsw i32 %sx, 1
br label %return
if.end5: ; preds = %if.else
%sub6 = sub nsw i32 %sx, %tx
br label %return
return: ; preds = %if.end5, %if.then4, %if.then
%retval.0 = phi i32 [ %sub, %if.then ], [ %add, %if.then4 ], [ %sub6, %if.end5 ]
ret i32 %retval.0
}