Fix a bug in which BranchProbabilityInfo wasn't setting branch weight…

…s of basic blocks inside loops correctly.

Previously, BranchProbabilityInfo::calcLoopBranchHeuristics would determine the weights of basic blocks inside loops even when it didn't have enough information to estimate the branch probabilities correctly. This patch fixes the function to exit early if it doesn't see any exit edges or back edges and let the later heuristics determine the weights.

This fixes PR18705 and <rdar://problem/15991090>.

Differential Revision: http://reviews.llvm.org/D3363

llvm-svn: 206194

llvm/lib/Analysis/BranchProbabilityInfo.cpp

@@ -322,6 +322,9 @@ bool BranchProbabilityInfo::calcLoopBranchHeuristics(BasicBlock *BB) {
       InEdges.push_back(I.getSuccessorIndex());
   }
 
+  if (BackEdges.empty() && ExitingEdges.empty())
+    return false;
+
   if (uint32_t numBackEdges = BackEdges.size()) {
     uint32_t backWeight = LBH_TAKEN_WEIGHT / numBackEdges;
     if (backWeight < NORMAL_WEIGHT)

llvm/test/Analysis/BranchProbabilityInfo/loop.ll

@@ -15,7 +15,7 @@ do.body:
   %i.0 = phi i32 [ 0, %entry ], [ %inc3, %do.end ]
   call void @g1()
   br label %do.body1
-; CHECK: edge do.body -> do.body1 probability is 124 / 124 = 100%
+; CHECK: edge do.body -> do.body1 probability is 16 / 16 = 100%
 
 do.body1:
   %j.0 = phi i32 [ 0, %do.body ], [ %inc, %do.body1 ]
@@ -55,8 +55,8 @@ for.body:
   %i.010 = phi i32 [ 0, %for.body.lr.ph ], [ %inc5, %for.end ]
   call void @g1()
   br i1 %cmp27, label %for.body3, label %for.end
-; CHECK: edge for.body -> for.body3 probability is 62 / 124 = 50%
-; CHECK: edge for.body -> for.end probability is 62 / 124 = 50%
+; CHECK: edge for.body -> for.body3 probability is 20 / 32 = 62.5%
+; CHECK: edge for.body -> for.end probability is 12 / 32 = 37.5%
 
 for.body3:
   %j.08 = phi i32 [ %inc, %for.body3 ], [ 0, %for.body ]
@@ -91,8 +91,8 @@ do.body:
   %0 = load i32* %c, align 4
   %cmp = icmp slt i32 %0, 42
   br i1 %cmp, label %do.body1, label %if.end
-; CHECK: edge do.body -> do.body1 probability is 62 / 124 = 50%
-; CHECK: edge do.body -> if.end probability is 62 / 124 = 50%
+; CHECK: edge do.body -> do.body1 probability is 16 / 32 = 50%
+; CHECK: edge do.body -> if.end probability is 16 / 32 = 50%
 
 do.body1:
   %j.0 = phi i32 [ %inc, %do.body1 ], [ 0, %do.body ]
@@ -165,7 +165,7 @@ do.body:
   %i.0 = phi i32 [ 0, %entry ], [ %inc4, %do.end ]
   call void @g1()
   br label %do.body1
-; CHECK: edge do.body -> do.body1 probability is 124 / 124 = 100%
+; CHECK: edge do.body -> do.body1 probability is 16 / 16 = 100%
 
 do.body1:
   %j.0 = phi i32 [ 0, %do.body ], [ %inc, %if.end ]
@@ -209,7 +209,7 @@ do.body:
   %i.0 = phi i32 [ 0, %entry ], [ %inc4, %do.end ]
   call void @g1()
   br label %do.body1
-; CHECK: edge do.body -> do.body1 probability is 124 / 124 = 100%
+; CHECK: edge do.body -> do.body1 probability is 16 / 16 = 100%
 
 do.body1:
   %j.0 = phi i32 [ 0, %do.body ], [ %inc, %do.cond ]
@@ -261,14 +261,14 @@ for.body:
   %0 = load i32* %c, align 4
   %cmp1 = icmp eq i32 %0, %i.011
   br i1 %cmp1, label %for.inc5, label %if.end
-; CHECK: edge for.body -> for.inc5 probability is 62 / 124 = 50%
-; CHECK: edge for.body -> if.end probability is 62 / 124 = 50%
+; CHECK: edge for.body -> for.inc5 probability is 16 / 32 = 50%
+; CHECK: edge for.body -> if.end probability is 16 / 32 = 50%
 
 if.end:
   call void @g1()
   br i1 %cmp38, label %for.body4, label %for.end
-; CHECK: edge if.end -> for.body4 probability is 62 / 124 = 50%
-; CHECK: edge if.end -> for.end probability is 62 / 124 = 50%
+; CHECK: edge if.end -> for.body4 probability is 20 / 32 = 62.5%
+; CHECK: edge if.end -> for.end probability is 12 / 32 = 37.5%
 
 for.body4:
   %j.09 = phi i32 [ %inc, %for.body4 ], [ 0, %if.end ]
@@ -282,7 +282,7 @@ for.body4:
 for.end:
   call void @g3()
   br label %for.inc5
-; CHECK: edge for.end -> for.inc5 probability is 124 / 124 = 100%
+; CHECK: edge for.end -> for.inc5 probability is 16 / 16 = 100%
 
 for.inc5:
   %inc6 = add nsw i32 %i.011, 1
@@ -314,35 +314,35 @@ for.body:
   %i.019 = phi i32 [ 0, %for.body.lr.ph ], [ %inc14, %for.end ]
   call void @g1()
   br i1 %cmp216, label %for.body3, label %for.end
-; CHECK: edge for.body -> for.body3 probability is 62 / 124 = 50%
-; CHECK: edge for.body -> for.end probability is 62 / 124 = 50%
+; CHECK: edge for.body -> for.body3 probability is 20 / 32 = 62.5%
+; CHECK: edge for.body -> for.end probability is 12 / 32 = 37.5%
 
 for.body3:
   %j.017 = phi i32 [ 0, %for.body ], [ %inc, %for.inc ]
   %0 = load i32* %c, align 4
   %cmp4 = icmp eq i32 %0, %j.017
   br i1 %cmp4, label %for.inc, label %if.end
-; CHECK: edge for.body3 -> for.inc probability is 62 / 124 = 50%
-; CHECK: edge for.body3 -> if.end probability is 62 / 124 = 50%
+; CHECK: edge for.body3 -> for.inc probability is 16 / 32 = 50%
+; CHECK: edge for.body3 -> if.end probability is 16 / 32 = 50%
 
 if.end:
   %1 = load i32* %arrayidx5, align 4
   %cmp6 = icmp eq i32 %1, %j.017
   br i1 %cmp6, label %for.inc, label %if.end8
-; CHECK: edge if.end -> for.inc probability is 62 / 124 = 50%
-; CHECK: edge if.end -> if.end8 probability is 62 / 124 = 50%
+; CHECK: edge if.end -> for.inc probability is 16 / 32 = 50%
+; CHECK: edge if.end -> if.end8 probability is 16 / 32 = 50%
 
 if.end8:
   %2 = load i32* %arrayidx9, align 4
   %cmp10 = icmp eq i32 %2, %j.017
   br i1 %cmp10, label %for.inc, label %if.end12
-; CHECK: edge if.end8 -> for.inc probability is 62 / 124 = 50%
-; CHECK: edge if.end8 -> if.end12 probability is 62 / 124 = 50%
+; CHECK: edge if.end8 -> for.inc probability is 16 / 32 = 50%
+; CHECK: edge if.end8 -> if.end12 probability is 16 / 32 = 50%
 
 if.end12:
   call void @g2()
   br label %for.inc
-; CHECK: edge if.end12 -> for.inc probability is 124 / 124 = 100%
+; CHECK: edge if.end12 -> for.inc probability is 16 / 16 = 100%
 
 for.inc:
   %inc = add nsw i32 %j.017, 1

llvm/test/Analysis/BranchProbabilityInfo/pr18705.ll

@@ -0,0 +1,58 @@
+; RUN: opt < %s -analyze -branch-prob | FileCheck %s
+
+; Since neither of while.body's out-edges is an exit or a back edge,
+; calcLoopBranchHeuristics should return early without setting the weights.
+; calcFloatingPointHeuristics, which is run later, sets the weights.
+;
+; CHECK: edge while.body -> if.then probability is 20 / 32 = 62.5%
+; CHECK: edge while.body -> if.else probability is 12 / 32 = 37.5%
+
+define void @foo1(i32 %n, i32* nocapture %b, i32* nocapture %c, i32* nocapture %d, float* nocapture readonly %f0, float* nocapture readonly %f1) {
+entry:
+  %tobool8 = icmp eq i32 %n, 0
+  br i1 %tobool8, label %while.end, label %while.body.lr.ph
+
+while.body.lr.ph:
+  %0 = sext i32 %n to i64
+  br label %while.body
+
+while.body:
+  %indvars.iv = phi i64 [ %0, %while.body.lr.ph ], [ %indvars.iv.next, %if.end ]
+  %b.addr.011 = phi i32* [ %b, %while.body.lr.ph ], [ %b.addr.1, %if.end ]
+  %d.addr.010 = phi i32* [ %d, %while.body.lr.ph ], [ %incdec.ptr4, %if.end ]
+  %c.addr.09 = phi i32* [ %c, %while.body.lr.ph ], [ %c.addr.1, %if.end ]
+  %indvars.iv.next = add nsw i64 %indvars.iv, -1
+  %arrayidx = getelementptr inbounds float* %f0, i64 %indvars.iv.next
+  %1 = load float* %arrayidx, align 4
+  %arrayidx2 = getelementptr inbounds float* %f1, i64 %indvars.iv.next
+  %2 = load float* %arrayidx2, align 4
+  %cmp = fcmp une float %1, %2
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %incdec.ptr = getelementptr inbounds i32* %b.addr.011, i64 1
+  %3 = load i32* %b.addr.011, align 4
+  %add = add nsw i32 %3, 12
+  store i32 %add, i32* %b.addr.011, align 4
+  br label %if.end
+
+if.else:
+  %incdec.ptr3 = getelementptr inbounds i32* %c.addr.09, i64 1
+  %4 = load i32* %c.addr.09, align 4
+  %sub = add nsw i32 %4, -13
+  store i32 %sub, i32* %c.addr.09, align 4
+  br label %if.end
+
+if.end:
+  %c.addr.1 = phi i32* [ %c.addr.09, %if.then ], [ %incdec.ptr3, %if.else ]
+  %b.addr.1 = phi i32* [ %incdec.ptr, %if.then ], [ %b.addr.011, %if.else ]
+  %incdec.ptr4 = getelementptr inbounds i32* %d.addr.010, i64 1
+  store i32 14, i32* %d.addr.010, align 4
+  %5 = trunc i64 %indvars.iv.next to i32
+  %tobool = icmp eq i32 %5, 0
+  br i1 %tobool, label %while.end, label %while.body
+
+while.end:
+  ret void
+}
+

llvm/test/CodeGen/ARM/ifcvt-branch-weight-bug.ll

@@ -24,7 +24,7 @@ entry:
 ; CHECK: BB#1: derived from LLVM BB %for.body
 ; CHECK: Successors according to CFG: BB#2(130023362) BB#4(62)
 for.body:
-  br i1 undef, label %for.cond.backedge, label %lor.lhs.false.i
+  br i1 undef, label %for.cond.backedge, label %lor.lhs.false.i, !prof !1
 
 for.cond.backedge:
   %tobool = icmp eq %classL* undef, null
@@ -60,3 +60,4 @@ declare void @_ZN1F10handleMoveEb(%classF*, i1 zeroext)
 declare void @_Z3fn1v()
 
 !0 = metadata !{metadata !"clang version 3.5"}
+!1 = metadata !{metadata !"branch_weights", i32 62, i32 62}