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[IfConversion] Only renormalize probabilities if branches are analyzable

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If a block has non-analyzable branches, the listed successors don't need
to add up to one. For example, if a block has a conditional tail call,
that tail call will not have a corresponding successor in the successor
list, but will still be a possible branch.

Differential Revision: https://reviews.llvm.org/D30556


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297054 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Krzysztof Parzyszek 2017-03-06 19:12:42 +00:00
parent b440d4eaba
commit a3e49c560a
2 changed files with 40 additions and 2 deletions
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6
lib/CodeGen/IfConversion.cpp
View File

@ -2148,7 +2148,8 @@ void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges) {
// unknown probabilities into known ones.
// FIXME: This usage is too tricky and in the future we would like to
// eliminate all unknown probabilities in MBB.
ToBBI.BB->normalizeSuccProbs();
if (ToBBI.IsBrAnalyzable)
ToBBI.BB->normalizeSuccProbs();
SmallVector<MachineBasicBlock *, 4> FromSuccs(FromMBB.succ_begin(),
FromMBB.succ_end());
@ -2228,7 +2229,8 @@ void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges) {
// Normalize the probabilities of ToBBI.BB's successors with all adjustment
// we've done above.
ToBBI.BB->normalizeSuccProbs();
if (ToBBI.IsBrAnalyzable && FromBBI.IsBrAnalyzable)
ToBBI.BB->normalizeSuccProbs();
ToBBI.Predicate.append(FromBBI.Predicate.begin(), FromBBI.Predicate.end());
FromBBI.Predicate.clear();

36
test/CodeGen/Hexagon/ifcvt-simple-bprob.ll Normal file
View File

@ -0,0 +1,36 @@
; RUN: llc -march=hexagon < %s
; Check that branch probabilities are set correctly after performing the
; simple variant of if-conversion. The converted block has a branch that
; is not analyzable.
target triple = "hexagon"
declare void @foo()
; CHECK-LABEL: danny
; CHECK: if (p0.new) jump:nt foo
define void @danny(i32 %x) {
%t0 = icmp sgt i32 %x, 0
br i1 %t0, label %tail, label %exit, !prof !0
tail:
tail call void @foo();
ret void
exit:
ret void
}
; CHECK-LABEL: sammy
; CHECK: if (!p0.new) jump:t foo
define void @sammy(i32 %x) {
%t0 = icmp sgt i32 %x, 0
br i1 %t0, label %exit, label %tail, !prof !0
tail:
tail call void @foo();
ret void
exit:
ret void
}
!0 = !{!"branch_weights", i32 1, i32 2000}