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[JumpThreading] Consider freeze as a zero-cost instruction 

This is a simple patch that makes freeze as a zero-cost instruction, as bitcast already is.

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D85023
This commit is contained in:
Juneyoung Lee 2020-08-04 17:22:36 +09:00
parent 3401f9706b
commit e0d99e9aaf
2 changed files with 14 additions and 9 deletions
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4
llvm/lib/Transforms/Scalar/JumpThreading.cpp
View File

@ -535,6 +535,10 @@ static unsigned getJumpThreadDuplicationCost(BasicBlock *BB,
if (isa<BitCastInst>(I) && I->getType()->isPointerTy())
continue;
// Freeze instruction is free, too.
if (isa<FreezeInst>(I))
continue;
// Bail out if this instruction gives back a token type, it is not possible
// to duplicate it if it is used outside this BB.
if (I->getType()->isTokenTy() && I->isUsedOutsideOfBlock(BB))

19
llvm/test/Transforms/JumpThreading/thread-two-bbs-threshold.ll
View File

@ -6,30 +6,31 @@ target triple = "x86_64-unknown-linux-gnu"
@a = global i32 0, align 4
; Show that freeze is not counted when comparing the cost with the threshold
define void @foo(i32 %cond1, i32 %cond2) {
; CHECK-LABEL: @foo(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TOBOOL:%.*]] = icmp eq i32 [[COND1:%.*]], 0
; CHECK-NEXT: br i1 [[TOBOOL]], label [[BB_COND2:%.*]], label [[BB_F1:%.*]]
; CHECK: bb.f1:
; CHECK-NEXT: call void @f1()
; CHECK-NEXT: br label [[BB_COND2]]
; CHECK-NEXT: br i1 [[TOBOOL]], label [[BB_COND2_THREAD:%.*]], label [[BB_COND2:%.*]]
; CHECK: bb.cond2:
; CHECK-NEXT: [[PTR:%.*]] = phi i32* [ null, [[BB_F1]] ], [ @a, [[ENTRY:%.*]] ]
; CHECK-NEXT: call void @f1()
; CHECK-NEXT: [[COND2_FR:%.*]] = freeze i32 [[COND2:%.*]]
; CHECK-NEXT: [[X:%.*]] = add i32 [[COND2_FR]], 1
; CHECK-NEXT: [[TOBOOL1:%.*]] = icmp eq i32 [[X]], 0
; CHECK-NEXT: br i1 [[TOBOOL1]], label [[BB_FILE:%.*]], label [[BB_F2:%.*]]
; CHECK-NEXT: br i1 [[TOBOOL1]], label [[BB_F4:%.*]], label [[BB_F2:%.*]]
; CHECK: bb.cond2.thread:
; CHECK-NEXT: [[COND2_FR2:%.*]] = freeze i32 [[COND2]]
; CHECK-NEXT: [[X3:%.*]] = add i32 [[COND2_FR2]], 1
; CHECK-NEXT: [[TOBOOL14:%.*]] = icmp eq i32 [[X3]], 0
; CHECK-NEXT: br i1 [[TOBOOL14]], label [[BB_F3:%.*]], label [[BB_F2]]
; CHECK: bb.f2:
; CHECK-NEXT: call void @f2()
; CHECK-NEXT: br label [[EXIT:%.*]]
; CHECK: bb.file:
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32* [[PTR]], null
; CHECK-NEXT: br i1 [[CMP]], label [[BB_F4:%.*]], label [[BB_F3:%.*]]
; CHECK: bb.f3:
; CHECK-NEXT: call void @f3()
; CHECK-NEXT: br label [[EXIT]]
; CHECK: bb.f4:
; CHECK-NEXT: [[PTR5:%.*]] = phi i32* [ null, [[BB_COND2]] ]
; CHECK-NEXT: call void @f4()
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit: