Do not set branch weight if the branch weight annotation is present.

Summary: ThinLTO will annotate the CFG twice. If the branch weight is set by the first annotation, we should not set the branch weight again in the second annotation because the first annotation is more accurate as there is less optimization that could affect debug info accuracy.

Reviewers: tejohnson, davidxl

Reviewed By: tejohnson

Subscribers: mehdi_amini, aprantl, llvm-commits

Differential Revision: https://reviews.llvm.org/D31228

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298602 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/IPO/SampleProfile.cpp b/lib/Transforms/IPO/SampleProfile.cpp
index e8a1acf3c9c85ea0b1a11acaf24560bdf580bc48..d2ccbd811bae9bb2470d30ffd93b16e4f0034a05 100644 (file)
--- a/lib/Transforms/IPO/SampleProfile.cpp
+++ b/lib/Transforms/IPO/SampleProfile.cpp
@@ -1162,9 +1162,13 @@ void SampleProfileLoader::propagateWeights(Function &F) {
       }
     }
 
+    uint64_t TempWeight;
     // Only set weights if there is at least one non-zero weight.
     // In any other case, let the analyzer set weights.
-    if (MaxWeight > 0) {
+    // Do not set weights if the weights are present. In ThinLTO, the profile
+    // annotation is done twice. If the first annotation already set the
+    // weights, the second pass does not need to set it.
+    if (MaxWeight > 0 && !TI->extractProfTotalWeight(TempWeight)) {
       DEBUG(dbgs() << "SUCCESS. Found non-zero weights.\n");
       TI->setMetadata(llvm::LLVMContext::MD_prof,
                       MDB.createBranchWeights(Weights));

diff --git a/test/Transforms/SampleProfile/branch.ll b/test/Transforms/SampleProfile/branch.ll
index 2ef01a76b0f0856ea14b68736c876c1f7cb3a740..5a5160e6343aa829eebfce75671412cff254c629 100644 (file)
--- a/test/Transforms/SampleProfile/branch.ll
+++ b/test/Transforms/SampleProfile/branch.ll
@@ -87,7 +87,9 @@ for.cond:                                         ; preds = %for.inc, %if.then.2
   %6 = load i32, i32* %u, align 4, !dbg !46
   %7 = load i32, i32* %limit, align 4, !dbg !48
   %cmp5 = icmp slt i32 %6, %7, !dbg !49
-  br i1 %cmp5, label %for.body, label %for.end, !dbg !50
+  br i1 %cmp5, label %for.body, label %for.end, !dbg !50, !prof !80
+; CHECK: edge for.cond -> for.body probability is 0x73333333 / 0x80000000 = 90.00%
+; CHECK: edge for.cond -> for.end probability is 0x0ccccccd / 0x80000000 = 10.00%
 
 for.body:                                         ; preds = %for.cond
   call void @llvm.dbg.declare(metadata double* %x, metadata !51, metadata !17), !dbg !53
@@ -237,3 +239,4 @@ attributes #4 = { nounwind readonly }
 !77 = !DILocation(line: 20, column: 4, scope: !6)
 !78 = !DILocation(line: 21, column: 4, scope: !6)
 !79 = !DILocation(line: 22, column: 2, scope: !6)
+!80 = !{!"branch_weights", i32 90, i32 10}