From ec63ff81dd85fcb1731ccfb07980a259cc974ee8 Mon Sep 17 00:00:00 2001
From: Jun Bum Lim <junbuml@codeaurora.org>
Date: Fri, 18 Dec 2015 20:53:47 +0000
Subject: [PATCH] Enhance BranchProbabilityInfo::calcUnreachableHeuristics for
 InvokeInst

When identifying blocks post-dominated by an unreachable-terminated block
in BranchProbabilityInfo, consider only the edge to the normal destination
block if the terminator is InvokeInst and let calcInvokeHeuristics() decide
edge weights for the InvokeInst.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256028 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/BranchProbabilityInfo.cpp        | 10 +++++
 .../BranchProbabilityInfo/noreturn.ll         | 45 +++++++++++++++++++
 .../CodeGen/X86/catchret-empty-fallthrough.ll |  6 ++-
 3 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/lib/Analysis/BranchProbabilityInfo.cpp b/lib/Analysis/BranchProbabilityInfo.cpp
index 6cdf43a06a9..a0d6123b583 100644
--- a/lib/Analysis/BranchProbabilityInfo.cpp
+++ b/lib/Analysis/BranchProbabilityInfo.cpp
@@ -147,6 +147,16 @@ bool BranchProbabilityInfo::calcUnreachableHeuristics(BasicBlock *BB) {
   if (TI->getNumSuccessors() == 1 || UnreachableEdges.empty())
     return false;
 
+  // If the terminator is an InvokeInst, check only the normal destination block
+  // as the unwind edge of InvokeInst is also very unlikely taken.
+  if (auto *II = dyn_cast<InvokeInst>(TI))
+    if (PostDominatedByUnreachable.count(II->getNormalDest())) {
+      PostDominatedByUnreachable.insert(BB);
+      // Return false here so that edge weights for InvokeInst could be decided
+      // in calcInvokeHeuristics().
+      return false;
+    }
+
   uint32_t UnreachableWeight =
     std::max(UR_TAKEN_WEIGHT / (unsigned)UnreachableEdges.size(), MIN_WEIGHT);
   for (SmallVectorImpl<unsigned>::iterator I = UnreachableEdges.begin(),
diff --git a/test/Analysis/BranchProbabilityInfo/noreturn.ll b/test/Analysis/BranchProbabilityInfo/noreturn.ll
index 63926370cda..513818d8da6 100644
--- a/test/Analysis/BranchProbabilityInfo/noreturn.ll
+++ b/test/Analysis/BranchProbabilityInfo/noreturn.ll
@@ -77,3 +77,48 @@ abort:
 exit:
   ret i32 %b
 }
+
+@_ZTIi = external global i8*
+
+; CHECK-LABEL: throwSmallException
+; CHECK-NOT: invoke i32 @smallFunction
+define i32 @throwSmallException(i32 %idx, i32 %limit) #0 personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+entry:
+  %cmp = icmp sge i32 %idx, %limit
+  br i1 %cmp, label %if.then, label %if.end
+; CHECK: edge entry -> if.then probability is 0x00000800 / 0x80000000 = 0.00%
+; CHECK: edge entry -> if.end probability is 0x7ffff800 / 0x80000000 = 100.00% [HOT edge]
+
+if.then:                                          ; preds = %entry
+  %exception = call i8* @__cxa_allocate_exception(i64 1) #0
+  invoke i32 @smallFunction(i32 %idx)
+          to label %invoke.cont unwind label %lpad
+; CHECK: edge if.then -> invoke.cont probability is 0x7ffff800 / 0x80000000 = 100.00% [HOT edge]
+; CHECK: edge if.then -> lpad probability is 0x00000800 / 0x80000000 = 0.00%
+
+invoke.cont:                                      ; preds = %if.then
+  call void @__cxa_throw(i8* %exception, i8* bitcast (i8** @_ZTIi  to i8*), i8* null) #1
+  unreachable
+
+lpad:                                             ; preds = %if.then
+  %ll = landingpad { i8*, i32 }
+          cleanup
+  ret i32 %idx
+
+if.end:                                           ; preds = %entry
+  ret i32 %idx
+}
+
+@a = global i32 4
+define i32 @smallFunction(i32 %a) {
+entry:
+  %r = load volatile i32, i32* @a
+  ret i32 %r
+}
+
+attributes #0 = { nounwind }
+attributes #1 = { noreturn }
+
+declare i8* @__cxa_allocate_exception(i64)
+declare i32 @__gxx_personality_v0(...)
+declare void @__cxa_throw(i8*, i8*, i8*)
diff --git a/test/CodeGen/X86/catchret-empty-fallthrough.ll b/test/CodeGen/X86/catchret-empty-fallthrough.ll
index 5405d570b15..7ad10330317 100644
--- a/test/CodeGen/X86/catchret-empty-fallthrough.ll
+++ b/test/CodeGen/X86/catchret-empty-fallthrough.ll
@@ -34,12 +34,14 @@ return:                                           ; preds = %catch, %entry
 
 ; CHECK-LABEL: foo: # @foo
 ; CHECK: testb $1, %cl
-; CHECK: jne .LBB0_[[return:[0-9]+]]
+; CHECK: je .LBB0_[[try:[0-9]+]]
+; CHECK: .LBB0_[[return:[0-9]+]]:
+; CHECK: retq
+; CHECK: .LBB0_[[try]]:
 ; CHECK: .Ltmp0:
 ; CHECK: callq bar
 ; CHECK: .Ltmp1:
 ; CHECK: .LBB0_[[catch:[0-9]+]]:
-; CHECK: .LBB0_[[return]]:
 
 ; CHECK: .seh_handlerdata
 ; CHECK-NEXT: .Lfoo$parent_frame_offset = 32
-- 
2.34.1