[JumpThreading] make jump threading respect convergent annotation.

Summary:
JumpThreading shouldn't duplicate a convergent call, because that would move a convergent call into a control-inequivalent location. For example,
  if (cond) {
    ...
  } else {
    ...
  }
  convergent_call();
  if (cond) {
    ...
  } else {
    ...
  }
should not be optimized to
  if (cond) {
    ...
    convergent_call();
    ...
  } else {
    ...
    convergent_call();
    ...
  }

Test Plan: test/Transforms/JumpThreading/basic.ll

Patch by Xuetian Weng.

Reviewers: resistor, arsenm, jingyue

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D12484

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@246415 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/IR/Instructions.h b/include/llvm/IR/Instructions.h
index 7037d898fddcc7e1749117e73d81edfe2946072b..f9dce102787f575f3714628e2ac8e3a80653d50e 100644 (file)
--- a/include/llvm/IR/Instructions.h
+++ b/include/llvm/IR/Instructions.h
@@ -1634,6 +1634,12 @@ public:
     addAttribute(AttributeSet::FunctionIndex, Attribute::NoDuplicate);
   }
 
+  /// \brief Determine if the call is convergent
+  bool isConvergent() const { return hasFnAttr(Attribute::Convergent); }
+  void setConvergent() {
+    addAttribute(AttributeSet::FunctionIndex, Attribute::Convergent);
+  }
+
   /// \brief Determine if the call returns a structure through first
   /// pointer argument.
   bool hasStructRetAttr() const {

diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index b87f4766e8dc94ea0bd980e0543d7d4fab0afe25..2d5aef88470634824208f7cc62850eab0a412927 100644 (file)
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -273,7 +273,7 @@ static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB,
     // as having cost of 2 total, and if they are a vector intrinsic, we model
     // them as having cost 1.
     if (const CallInst *CI = dyn_cast<CallInst>(I)) {
-      if (CI->cannotDuplicate())
+      if (CI->cannotDuplicate() || CI->isConvergent())
         // Blocks with NoDuplicate are modelled as having infinite cost, so they
         // are never duplicated.
         return ~0U;

diff --git a/test/Transforms/JumpThreading/basic.ll b/test/Transforms/JumpThreading/basic.ll
index 32cc4de9285a212aa12a8e5f3095e01e84ccecac..46c92bc1f577a7161bf64c14547d16885f2e4803 100644 (file)
--- a/test/Transforms/JumpThreading/basic.ll
+++ b/test/Transforms/JumpThreading/basic.ll
@@ -483,7 +483,7 @@ declare void @g()
 declare void @j()
 declare void @k()
 
-; CHECK: define void @h(i32 %p) {
+; CHECK-LABEL: define void @h(i32 %p) {
 define void @h(i32 %p) {
   %x = icmp ult i32 %p, 5
   br i1 %x, label %l1, label %l2
@@ -513,4 +513,36 @@ l5:
 ; CHECK: }
 }
 
+; CHECK-LABEL: define void @h_con(i32 %p) {
+define void @h_con(i32 %p) {
+  %x = icmp ult i32 %p, 5
+  br i1 %x, label %l1, label %l2
+
+l1:
+  call void @j()
+  br label %l3
+
+l2:
+  call void @k()
+  br label %l3
+
+l3:
+; CHECK: call void @g() [[CON:#[0-9]+]]
+; CHECK-NOT: call void @g() [[CON]]
+  call void @g() convergent
+  %y = icmp ult i32 %p, 5
+  br i1 %y, label %l4, label %l5
+
+l4:
+  call void @j()
+  ret void
+
+l5:
+  call void @k()
+  ret void
+; CHECK: }
+}
+
+
 ; CHECK: attributes [[NOD]] = { noduplicate }
+; CHECK: attributes [[CON]] = { convergent }