[llvm] r256028 - Enhance BranchProbabilityInfo::calcUnreachableHeuristics for InvokeInst

[Jun Bum Lim via llvm-commits]

Author: junbuml
Date: Fri Dec 18 14:53:47 2015
New Revision: 256028

URL: http://llvm.org/viewvc/llvm-project?rev=256028&view=rev
Log:
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.

Modified:
    llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp
    llvm/trunk/test/Analysis/BranchProbabilityInfo/noreturn.ll
    llvm/trunk/test/CodeGen/X86/catchret-empty-fallthrough.ll

Modified: llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp?rev=256028&r1=256027&r2=256028&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp (original)
+++ llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp Fri Dec 18 14:53:47 2015
@@ -147,6 +147,16 @@ bool BranchProbabilityInfo::calcUnreacha
   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(),

Modified: llvm/trunk/test/Analysis/BranchProbabilityInfo/noreturn.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BranchProbabilityInfo/noreturn.ll?rev=256028&r1=256027&r2=256028&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/BranchProbabilityInfo/noreturn.ll (original)
+++ llvm/trunk/test/Analysis/BranchProbabilityInfo/noreturn.ll Fri Dec 18 14:53:47 2015
@@ -77,3 +77,48 @@ abort:
 exit:
   ret i32 %b
 }
+
+ at _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
+}
+
+ at 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*)

Modified: llvm/trunk/test/CodeGen/X86/catchret-empty-fallthrough.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/catchret-empty-fallthrough.ll?rev=256028&r1=256027&r2=256028&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/catchret-empty-fallthrough.ll (original)
+++ llvm/trunk/test/CodeGen/X86/catchret-empty-fallthrough.ll Fri Dec 18 14:53:47 2015
@@ -34,12 +34,14 @@ return:
 
 ; 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