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[JumpThreading] make jump threading respect convergent annotation.

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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

llvm-svn: 246415
This commit is contained in:
Jingyue Wu 2015-08-31 06:10:27 +00:00
parent 3827771c05
commit 02e7637de1
3 changed files with 40 additions and 2 deletions
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6
include/llvm/IR/Instructions.h
View File

@ -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 {

2
lib/Transforms/Scalar/JumpThreading.cpp
View File

@ -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;

34
test/Transforms/JumpThreading/basic.ll
View File

@ -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 }