[PATCH] D19948: Propagate branch metadata when some branch probability is missing.

[Dehao Chen via llvm-commits]

danielcdh created this revision.
danielcdh added reviewers: davidxl, spatel, hfinkel.
danielcdh added a subscriber: llvm-commits.

In sample profile, some branches may have profile missing due to profile inaccuracy. We want existing branch probability still valid after propagation.

http://reviews.llvm.org/D19948

Files:
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/Transforms/SimplifyCFG/preserve-branchweights.ll

Index: test/Transforms/SimplifyCFG/preserve-branchweights.ll
===================================================================
--- test/Transforms/SimplifyCFG/preserve-branchweights.ll
+++ test/Transforms/SimplifyCFG/preserve-branchweights.ll
@@ -464,6 +464,30 @@
   ret i32 %outval
 }
 
+define i32 @SimplifyCondBranchToCondBranchSwapMissingWeight(i1 %cmpa, i1 %cmpb) {
+; CHECK-LABEL: @SimplifyCondBranchToCondBranchSwapMissingWeight(
+; CHECK-NEXT:  block1:
+; CHECK-NEXT:    [[CMPA_NOT:%.*]] = xor i1 %cmpa, true 
+; CHECK-NEXT:    [[CMPB_NOT:%.*]] = xor i1 %cmpb, true
+; CHECK-NEXT:    [[BRMERGE:%.*]] = or i1 [[CMPA_NOT]], [[CMPB_NOT]]
+; CHECK-NEXT:    [[DOTMUX:%.*]] = select i1 [[CMPA_NOT]], i32 0, i32 2, !prof !16
+; CHECK-NEXT:    [[OUTVAL:%.*]] = select i1 [[BRMERGE]], i32 [[DOTMUX]], i32 1, !prof !17
+; CHECK-NEXT:    ret i32 [[OUTVAL]]
+;
+block1:
+  br i1 %cmpa, label %block2, label %block3, !prof !13
+
+block2:
+  br i1 %cmpb, label %exit, label %block3
+
+block3:
+  %cowval = phi i32 [ 2, %block2 ], [ 0, %block1 ]
+  br label %exit
+
+exit:
+  %outval = phi i32 [ %cowval, %block3 ], [ 1, %block2 ]
+  ret i32 %outval
+}
 
 !0 = !{!"branch_weights", i32 3, i32 5}
 !1 = !{!"branch_weights", i32 1, i32 1}
@@ -499,4 +523,6 @@
 ; CHECK: !13 = !{!"branch_weights", i32 34, i32 21}
 ; CHECK: !14 = !{!"branch_weights", i32 33, i32 14}
 ; CHECK: !15 = !{!"branch_weights", i32 47, i32 8}
+; CHECK: !16 = !{!"branch_weights", i32 6, i32 2}
+; CHECK: !17 = !{!"branch_weights", i32 8, i32 2}
 
Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2843,10 +2843,18 @@
   MDBuilder MDB(BI->getContext());
   uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
   uint64_t PredCommon, PredOther, SuccCommon, SuccOther;
-  bool HasWeights = PBI->extractProfMetadata(PredTrueWeight, PredFalseWeight);
-  if (HasWeights)
-    HasWeights = BI->extractProfMetadata(SuccTrueWeight, SuccFalseWeight);
+  bool PredHasWeights =
+      PBI->extractProfMetadata(PredTrueWeight, PredFalseWeight);
+  bool SuccHasWeights =
+      BI->extractProfMetadata(SuccTrueWeight, SuccFalseWeight);
+  bool HasWeights = PredHasWeights || SuccHasWeights;
   if (HasWeights) {
+    if (!PredHasWeights) {
+      PredFalseWeight = PredTrueWeight = 1;
+    }
+    if (!SuccHasWeights) {
+      SuccFalseWeight = SuccTrueWeight = 1;
+    }
     PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
     PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
     SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;


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