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Chijun Sima 28625d59d9 [TailCallElim] Preserve DT and PDT
Summary:
Previously, in the NewPM pipeline, TailCallElim recalculates the DomTree when it modifies any instruction in the Function.
For example,
```
CallInst *CI = dyn_cast<CallInst>(&I);
...
CI->setTailCall();
Modified = true;
...
if (!Modified || ...)
  return PreservedAnalyses::all();
```
After applying this patch, the DomTree only recalculates if needed (plus an extra insertEdge() + an extra deleteEdge() call).

When optimizing SQLite with `-passes="default<O3>"` pipeline of the newPM, the number of DomTree recalculation decreases by 6.2%, the number of nodes visited by DFS decreases by 2.9%. The time used by DomTree will decrease approximately 1%~2.5% after applying the patch.
 
Statistics:
```
Before the patch:
 23010 dom-tree-stats               - Number of DomTree recalculations
489264 dom-tree-stats               - Number of nodes visited by DFS -- DomTree
After the patch:
 21581 dom-tree-stats               - Number of DomTree recalculations
475088 dom-tree-stats               - Number of nodes visited by DFS -- DomTree
```

Reviewers: kuhar, dmgreen, brzycki, grosser, davide

Reviewed By: kuhar, brzycki

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D49982

llvm-svn: 338954
2018-08-04 08:13:47 +00:00

30 lines
564 B
LLVM

; RUN: opt < %s -tailcallelim -verify-dom-info -S | FileCheck %s
; Test that we don't tail call in a functions that calls returns_twice
; functions.
declare void @bar()
; CHECK: foo1
; CHECK-NOT: tail call void @bar()
define void @foo1(i32* %x) {
bb:
%tmp75 = tail call i32 @setjmp(i32* %x)
call void @bar()
ret void
}
declare i32 @setjmp(i32*) returns_twice
; CHECK: foo2
; CHECK-NOT: tail call void @bar()
define void @foo2(i32* %x) {
bb:
%tmp75 = tail call i32 @zed2(i32* %x)
call void @bar()
ret void
}
declare i32 @zed2(i32*) returns_twice