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PGO branch weight: keep halving the weights until they can fit into

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uint32.

When folding branches to common destination, the updated branch weights
can exceed uint32 by more than factor of 2. We should keep halving the
weights until they can fit into uint32.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200262 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manman Ren 2014-01-27 23:39:03 +00:00
parent 01df6842c1
commit aa6627016f
2 changed files with 44 additions and 13 deletions
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25
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -748,21 +748,22 @@ static void GetBranchWeights(TerminatorInst *TI,
}
}
/// Sees if any of the weights are too big for a uint32_t, and halves all the
/// weights if any are.
/// Keep halving the weights until all can fit in uint32_t.
static void FitWeights(MutableArrayRef<uint64_t> Weights) {
bool Halve = false;
for (unsigned i = 0; i < Weights.size(); ++i)
if (Weights[i] > UINT_MAX) {
Halve = true;
break;
}
while (true) {
bool Halve = false;
for (unsigned i = 0; i < Weights.size(); ++i)
if (Weights[i] > UINT_MAX) {
Halve = true;
break;
}
if (! Halve)
return;
if (! Halve)
return;
for (unsigned i = 0; i < Weights.size(); ++i)
Weights[i] /= 2;
for (unsigned i = 0; i < Weights.size(); ++i)
Weights[i] /= 2;
}
}
/// FoldValueComparisonIntoPredecessors - The specified terminator is a value

32
test/Transforms/SimplifyCFG/preserve-branchweights.ll
View File

@ -338,6 +338,32 @@ c:
ret void
}
;; When folding branches to common destination, the updated branch weights
;; can exceed uint32 by more than factor of 2. We should keep halving the
;; weights until they can fit into uint32.
@max_regno = common global i32 0, align 4
define void @test14(i32* %old, i32 %final) {
; CHECK-LABEL: @test14
; CHECK: br i1 %or.cond, label %for.exit, label %for.inc, !prof !10
for.cond:
br label %for.cond2
for.cond2:
%i.1 = phi i32 [ %inc19, %for.inc ], [ 0, %for.cond ]
%bit.0 = phi i32 [ %shl, %for.inc ], [ 1, %for.cond ]
%tobool = icmp eq i32 %bit.0, 0
br i1 %tobool, label %for.exit, label %for.body3, !prof !10
for.body3:
%v3 = load i32* @max_regno, align 4
%cmp4 = icmp eq i32 %i.1, %v3
br i1 %cmp4, label %for.exit, label %for.inc, !prof !11
for.inc:
%shl = shl i32 %bit.0, 1
%inc19 = add nsw i32 %i.1, 1
br label %for.cond2
for.exit:
ret void
}
!0 = metadata !{metadata !"branch_weights", i32 3, i32 5}
!1 = metadata !{metadata !"branch_weights", i32 1, i32 1}
!2 = metadata !{metadata !"branch_weights", i32 1, i32 2}
@ -348,6 +374,8 @@ c:
!7 = metadata !{metadata !"branch_weights", i32 33, i32 9, i32 8, i32 7}
!8 = metadata !{metadata !"branch_weights", i32 33, i32 9, i32 8}
!9 = metadata !{metadata !"branch_weights", i32 7, i32 6}
!10 = metadata !{metadata !"branch_weights", i32 672646, i32 21604207}
!11 = metadata !{metadata !"branch_weights", i32 6960, i32 21597248}
; CHECK: !0 = metadata !{metadata !"branch_weights", i32 5, i32 11}
; CHECK: !1 = metadata !{metadata !"branch_weights", i32 1, i32 5}
@ -359,4 +387,6 @@ c:
; CHECK: !7 = metadata !{metadata !"branch_weights", i32 17, i32 9, i32 8, i32 7, i32 17}
; CHECK: !8 = metadata !{metadata !"branch_weights", i32 24, i32 33}
; CHECK: !9 = metadata !{metadata !"branch_weights", i32 8, i32 33}
; CHECK-NOT: !9
;; The false weight prints out as a negative integer here, but inside llvm, we
;; treat the weight as an unsigned integer.
; CHECK: !10 = metadata !{metadata !"branch_weights", i32 112017436, i32 -735157296}