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CodeGen: Don't create branch weight metadata from empty profiles 

If all of our weights are zero when calculating branch weights, it
means we haven't profiled the code in question. Avoid creating a
metadata node that says all branches are equally likely in this case.

The test also checks constructs that hit the other createBranchWeights
overload. These were already working.

llvm-svn: 205606
This commit is contained in:
Justin Bogner 2014-04-04 02:48:51 +00:00
parent 08d57b951c
commit f3aefca7c1
3 changed files with 106 additions and 2 deletions
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8
clang/lib/CodeGen/CodeGenPGO.cpp
View File

@ -1004,9 +1004,13 @@ llvm::MDNode *CodeGenPGO::createBranchWeights(ArrayRef<uint64_t> Weights) {
if (Weights.size() < 2)
return nullptr;
// Check for empty weights.
uint64_t MaxWeight = *std::max_element(Weights.begin(), Weights.end());
if (MaxWeight == 0)
return nullptr;
// Calculate how to scale down to 32-bits.
uint64_t Scale = calculateWeightScale(*std::max_element(Weights.begin(),
Weights.end()));
uint64_t Scale = calculateWeightScale(MaxWeight);
SmallVector<uint32_t, 16> ScaledWeights;
ScaledWeights.reserve(Weights.size());

32
clang/test/Profile/Inputs/c-unprofiled-blocks.profdata Normal file
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@ -0,0 +1,32 @@
never_called
9
9
0
0
0
0
0
0
0
0
0
main
1
1
1
dead_code
10
10
1
0
0
0
0
0
0
0
0
0

68
clang/test/Profile/c-unprofiled-blocks.c Normal file
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@ -0,0 +1,68 @@
// Blocks that we have no profile data for (ie, it was never reached in training
// runs) shouldn't have any branch weight metadata added.
// RUN: %clang_cc1 -triple x86_64-apple-macosx10.9 -main-file-name c-unprofiled-blocks.c %s -o - -emit-llvm -fprofile-instr-use=%S/Inputs/c-unprofiled-blocks.profdata | FileCheck -check-prefix=PGOUSE %s
// PGOUSE-LABEL: @never_called(i32 %i)
int never_called(int i) {
// PGOUSE: br i1 %{{[^,]*}}, label %{{[^,]*}}, label %{{[^,]*}}{{$}}
if (i) {}
// PGOUSE: br i1 %{{[^,]*}}, label %{{[^,]*}}, label %{{[^,]*}}{{$}}
for (i = 0; i < 100; ++i) {
}
// PGOUSE: br i1 %{{[^,]*}}, label %{{[^,]*}}, label %{{[^,]*}}{{$}}
while (--i) {}
// PGOUSE: br i1 %{{[^,]*}}, label %{{[^,]*}}, label %{{[^,]*}}{{$}}
do {} while (i++ < 75);
// PGOUSE: switch {{.*}} [
// PGOUSE-NEXT: i32 12
// PGOUSE-NEXT: i32 82
// PGOUSE-NEXT: ]{{$}}
switch (i) {
case 12: return 3;
case 82: return 0;
default: return 89;
}
}
// PGOUSE-LABEL: @dead_code(i32 %i)
int dead_code(int i) {
// PGOUSE: br {{.*}}, !prof !{{[0-9]+}}
if (i) {
// This branch is never reached.
// PGOUSE: br i1 %{{[^,]*}}, label %{{[^,]*}}, label %{{[^,]*}}{{$}}
if (!i) {}
// PGOUSE: br i1 %{{[^,]*}}, label %{{[^,]*}}, label %{{[^,]*}}{{$}}
for (i = 0; i < 100; ++i) {
}
// PGOUSE: br i1 %{{[^,]*}}, label %{{[^,]*}}, label %{{[^,]*}}{{$}}
while (--i) {}
// PGOUSE: br i1 %{{[^,]*}}, label %{{[^,]*}}, label %{{[^,]*}}{{$}}
do {} while (i++ < 75);
// PGOUSE: switch {{.*}} [
// PGOUSE-NEXT: i32 12
// PGOUSE-NEXT: i32 82
// PGOUSE-NEXT: ]{{$}}
switch (i) {
case 12: return 3;
case 82: return 0;
default: return 89;
}
}
return 2;
}
// PGOUSE-LABEL: @main(i32 %argc, i8** %argv)
int main(int argc, const char *argv[]) {
dead_code(0);
return 0;
}