Revert "[SimplifyCFG] propagate branch metadata when creating select"

MemorySanitizer: use-of-uninitialized-value
0x4910e47 in count /mnt/b/sanitizer-buildbot2/sanitizer-x86_64-linux-bootstrap/build/llvm/include/llvm/Support/MathExtras.h:159:12
0x4910e47 in countLeadingZeros<unsigned long> /mnt/b/sanitizer-buildbot2/sanitizer-x86_64-linux-bootstrap/build/llvm/include/llvm/Support/MathExtras.h:183
0x4910e47 in FitWeights /mnt/b/sanitizer-buildbot2/sanitizer-x86_64-linux-bootstrap/build/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:855
0x4910e47 in SimplifyCondBranchToCondBranch /mnt/b/sanitizer-buildbot2/sanitizer-x86_64-linux-bootstrap/build/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:2895

This reverts commit 609f4dd.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268577 91177308-0d34-0410-b5e6-96231b3b80d8

Author: vitalybuka

lib/Transforms/Utils/SimplifyCFG.cpp

@@ -848,7 +848,7 @@ static void GetBranchWeights(TerminatorInst *TI,
   }
 }
 
-/// Scale each weight so they all fit in uint32_t.
+/// Keep halving the weights until all can fit in uint32_t.
 static void FitWeights(MutableArrayRef<uint64_t> Weights) {
   uint64_t Max = *std::max_element(Weights.begin(), Weights.end());
   if (Max > UINT_MAX) {
@@ -2840,27 +2840,28 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
   PBI->setSuccessor(1, OtherDest);
 
   // Update branch weight for PBI.
-  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);
-  if (HasWeights) {
-    PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
-    PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
-    SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
-    SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
+  bool PredHasWeights =
+      PBI->extractProfMetadata(PredTrueWeight, PredFalseWeight);
+  bool SuccHasWeights =
+      BI->extractProfMetadata(SuccTrueWeight, SuccFalseWeight);
+  if (PredHasWeights && SuccHasWeights) {
+    uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
+    uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight;
+    uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
+    uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
     // The weight to CommonDest should be PredCommon * SuccTotal +
     //                                    PredOther * SuccCommon.
     // The weight to OtherDest should be PredOther * SuccOther.
     uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther) +
                                   PredOther * SuccCommon,
                               PredOther * SuccOther};
+    // Halve the weights if any of them cannot fit in an uint32_t
     FitWeights(NewWeights);
 
     PBI->setMetadata(LLVMContext::MD_prof,
-                     MDB.createBranchWeights(NewWeights[0], NewWeights[1]));
+                     MDBuilder(BI->getContext())
+                         .createBranchWeights(NewWeights[0], NewWeights[1]));
   }
 
   // OtherDest may have phi nodes.  If so, add an entry from PBI's
@@ -2879,24 +2880,9 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
     Value *PBIV = PN->getIncomingValue(PBBIdx);
     if (BIV != PBIV) {
       // Insert a select in PBI to pick the right value.
-      SelectInst *NV = cast<SelectInst>
+      Value *NV = cast<SelectInst>
         (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName() + ".mux"));
       PN->setIncomingValue(PBBIdx, NV);
-      // Although the select has the same condition as PBI, the original branch
-      // weights for PBI do not apply to the new select because the select's
-      // 'logical' edges are incoming edges of the phi that is eliminated, not
-      // the outgoing edges of PBI.
-      if (HasWeights) {
-        // The weight to PredCommonDest should be PredCommon * SuccTotal.
-        // The weight to PredOtherDest should be PredOther * SuccCommon.
-        uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther),
-                                  PredOther * SuccCommon};
-
-        FitWeights(NewWeights);
-
-        NV->setMetadata(LLVMContext::MD_prof,
-                        MDB.createBranchWeights(NewWeights[0], NewWeights[1]));
-      }
     }
   }
 

test/Transforms/SimplifyCFG/preserve-branchweights.ll

@@ -412,48 +412,22 @@ return:
   ret i32 %retval.0
 }
 
-; The selects should have freshly calculated branch weights.
+; The 1st select should have branch weights equal to the 1st branch.
+; The 2nd select should have freshly calculated branch weights.
 
 define i32 @SimplifyCondBranchToCondBranch(i1 %cmpa, i1 %cmpb) {
 ; CHECK-LABEL: @SimplifyCondBranchToCondBranch(
 ; CHECK-NEXT:  block1:
-; CHECK-NEXT:    [[BRMERGE:%.*]] = or i1 %cmpa, %cmpb
-; CHECK-NEXT:    [[DOTMUX:%.*]] = select i1 %cmpa, i32 0, i32 2, !prof !12
-; CHECK-NEXT:    [[OUTVAL:%.*]] = select i1 [[BRMERGE]], i32 [[DOTMUX]], i32 1, !prof !13
+; CHECK-NEXT:    [[BRMERGE:%.*]] = or i1 %cmpb, %cmpa
+; CHECK-NEXT:    [[DOTMUX:%.*]] = select i1 %cmpb, i32 0, i32 2
+; CHECK-NEXT:    [[OUTVAL:%.*]] = select i1 [[BRMERGE]], i32 [[DOTMUX]], i32 1, !prof !12
 ; CHECK-NEXT:    ret i32 [[OUTVAL]]
 ;
 block1:
-  br i1 %cmpa, label %block3, label %block2, !prof !13
+  br i1 %cmpb, label %block3, label %block2, !prof !0
 
 block2:
-  br i1 %cmpb, label %block3, label %exit, !prof !14
-
-block3:
-  %cowval = phi i32 [ 2, %block2 ], [ 0, %block1 ]
-  br label %exit
-
-exit:
-  %outval = phi i32 [ %cowval, %block3 ], [ 1, %block2 ]
-  ret i32 %outval
-}
-
-; Swap the operands of the compares to verify that the weights update correctly.
-
-define i32 @SimplifyCondBranchToCondBranchSwap(i1 %cmpa, i1 %cmpb) {
-; CHECK-LABEL: @SimplifyCondBranchToCondBranchSwap(
-; 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 !14
-; CHECK-NEXT:    [[OUTVAL:%.*]] = select i1 [[BRMERGE]], i32 [[DOTMUX]], i32 1, !prof !15
-; CHECK-NEXT:    ret i32 [[OUTVAL]]
-;
-block1:
-  br i1 %cmpa, label %block2, label %block3, !prof !13
-
-block2:
-  br i1 %cmpb, label %exit, label %block3, !prof !14
+  br i1 %cmpa, label %block3, label %exit, !prof !2
 
 block3:
   %cowval = phi i32 [ 2, %block2 ], [ 0, %block1 ]
@@ -478,8 +452,6 @@ exit:
 !10 = !{!"branch_weights", i32 672646, i32 21604207}
 !11 = !{!"branch_weights", i32 6960, i32 21597248}
 !12 = !{!"these_are_not_the_branch_weights_you_are_looking_for", i32 3, i32 5}
-!13 = !{!"branch_weights", i32 2, i32 3}
-!14 = !{!"branch_weights", i32 4, i32 7}
 
 ; CHECK: !0 = !{!"branch_weights", i32 5, i32 11}
 ; CHECK: !1 = !{!"branch_weights", i32 1, i32 5}
@@ -495,8 +467,5 @@ exit:
 ;; treat the weight as an unsigned integer.
 ; CHECK: !10 = !{!"branch_weights", i32 112017436, i32 -735157296}
 ; CHECK: !11 = !{!"branch_weights", i32 3, i32 5}
-; CHECK: !12 = !{!"branch_weights", i32 22, i32 12}
-; 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: !12 = !{!"branch_weights", i32 14, i32 10}