r205606 - CodeGen: Don't create branch weight metadata from empty profiles
Justin Bogner
mail at justinbogner.com
Thu Apr 3 19:48:51 PDT 2014
Author: bogner
Date: Thu Apr 3 21:48:51 2014
New Revision: 205606
URL: http://llvm.org/viewvc/llvm-project?rev=205606&view=rev
Log:
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.
Added:
cfe/trunk/test/Profile/Inputs/c-unprofiled-blocks.profdata
cfe/trunk/test/Profile/c-unprofiled-blocks.c
Modified:
cfe/trunk/lib/CodeGen/CodeGenPGO.cpp
Modified: cfe/trunk/lib/CodeGen/CodeGenPGO.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenPGO.cpp?rev=205606&r1=205605&r2=205606&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CodeGenPGO.cpp (original)
+++ cfe/trunk/lib/CodeGen/CodeGenPGO.cpp Thu Apr 3 21:48:51 2014
@@ -1004,9 +1004,13 @@ llvm::MDNode *CodeGenPGO::createBranchWe
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());
Added: cfe/trunk/test/Profile/Inputs/c-unprofiled-blocks.profdata
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Profile/Inputs/c-unprofiled-blocks.profdata?rev=205606&view=auto
==============================================================================
--- cfe/trunk/test/Profile/Inputs/c-unprofiled-blocks.profdata (added)
+++ cfe/trunk/test/Profile/Inputs/c-unprofiled-blocks.profdata Thu Apr 3 21:48:51 2014
@@ -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
+
Added: cfe/trunk/test/Profile/c-unprofiled-blocks.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Profile/c-unprofiled-blocks.c?rev=205606&view=auto
==============================================================================
--- cfe/trunk/test/Profile/c-unprofiled-blocks.c (added)
+++ cfe/trunk/test/Profile/c-unprofiled-blocks.c Thu Apr 3 21:48:51 2014
@@ -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;
+}
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