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[BPI] Look through bitcasts in calcZeroHeuristic 

Constant hoisting may have hidden a constant behind a bitcast so that
it isn't folded into its users. However, this prevents BPI from
calculating some of its heuristics that are based upon constant
values. So, I've added a simple helper function to look through these
casts.

Differential Revision: https://reviews.llvm.org/D58166

llvm-svn: 354119
This commit is contained in:
Sam Parker 2019-02-15 11:50:21 +00:00
parent 136f09bea1
commit 0b53e8454b
2 changed files with 110 additions and 1 deletions
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8
llvm/lib/Analysis/BranchProbabilityInfo.cpp
View File

@ -660,8 +660,14 @@ bool BranchProbabilityInfo::calcZeroHeuristics(const BasicBlock *BB,
if (!CI)
return false;
auto GetConstantInt = [](Value *V) {
if (auto *I = dyn_cast<BitCastInst>(V))
return dyn_cast<ConstantInt>(I->getOperand(0));
return dyn_cast<ConstantInt>(V);
};
Value *RHS = CI->getOperand(1);
ConstantInt *CV = dyn_cast<ConstantInt>(RHS);
ConstantInt *CV = GetConstantInt(RHS);
if (!CV)
return false;

103
llvm/test/Analysis/BranchProbabilityInfo/zero_heuristics.ll Normal file
View File

@ -0,0 +1,103 @@
; RUN: opt < %s -analyze -branch-prob | FileCheck %s
@A = global i32 0, align 4
@B = global i32 0, align 4
; CHECK-LABEL: eq_opaque_minus_one
define void @eq_opaque_minus_one(i32* %base) {
entry:
%const = bitcast i32 -1 to i32
%tmp1 = load i32, i32* @B, align 4
br label %for.body
; CHECK: edge for.body -> if.then probability is 0x30000000 / 0x80000000 = 37.50%
; CHECK: edge for.body -> for.inc probability is 0x50000000 / 0x80000000 = 62.50%
for.body:
%tmp4 = phi i32 [ %tmp1, %entry ], [ %tmp7, %for.inc ]
%inc.iv = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
%storemerge176.in = getelementptr inbounds i32, i32* %base, i32 %inc.iv
%storemerge176 = load i32, i32* %storemerge176.in, align 4
store i32 %storemerge176, i32* @A, align 4
%cmp20 = icmp eq i32 %storemerge176, %const
br i1 %cmp20, label %if.then, label %for.inc
if.then:
%lnot.ext = zext i1 %cmp20 to i32
store i32 %lnot.ext, i32* @B, align 4
br label %for.inc
for.inc:
%tmp7 = phi i32 [ %tmp4, %for.body ], [ %lnot.ext, %if.then ]
%inc = add nuw nsw i32 %inc.iv, 1
%cmp9 = icmp ult i32 %inc, 401
br i1 %cmp9, label %for.body, label %exit
exit:
ret void
}
; CHECK-LABEL: ne_opaque_minus_one
define void @ne_opaque_minus_one(i32* %base) {
entry:
%const = bitcast i32 -1 to i32
%tmp1 = load i32, i32* @B, align 4
br label %for.body
; CHECK: edge for.body -> if.then probability is 0x50000000 / 0x80000000 = 62.50%
; CHECK: edge for.body -> for.inc probability is 0x30000000 / 0x80000000 = 37.50%
for.body:
%tmp4 = phi i32 [ %tmp1, %entry ], [ %tmp7, %for.inc ]
%inc.iv = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
%storemerge176.in = getelementptr inbounds i32, i32* %base, i32 %inc.iv
%storemerge176 = load i32, i32* %storemerge176.in, align 4
store i32 %storemerge176, i32* @A, align 4
%cmp20 = icmp ne i32 %storemerge176, %const
br i1 %cmp20, label %if.then, label %for.inc
if.then:
%lnot.ext = zext i1 %cmp20 to i32
store i32 %lnot.ext, i32* @B, align 4
br label %for.inc
for.inc:
%tmp7 = phi i32 [ %tmp4, %for.body ], [ %lnot.ext, %if.then ]
%inc = add nuw nsw i32 %inc.iv, 1
%cmp9 = icmp ult i32 %inc, 401
br i1 %cmp9, label %for.body, label %exit
exit:
ret void
}
; CHECK-LABEL: sgt_opaque_minus_one
define void @sgt_opaque_minus_one(i32* %base) {
entry:
%const = bitcast i32 -1 to i32
%tmp1 = load i32, i32* @B, align 4
br label %for.body
; CHECK: edge for.body -> if.then probability is 0x50000000 / 0x80000000 = 62.50%
; CHECK: edge for.body -> for.inc probability is 0x30000000 / 0x80000000 = 37.50%
for.body:
%tmp4 = phi i32 [ %tmp1, %entry ], [ %tmp7, %for.inc ]
%inc.iv = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
%storemerge176.in = getelementptr inbounds i32, i32* %base, i32 %inc.iv
%storemerge176 = load i32, i32* %storemerge176.in, align 4
store i32 %storemerge176, i32* @A, align 4
%cmp20 = icmp sgt i32 %storemerge176, %const
br i1 %cmp20, label %if.then, label %for.inc
if.then:
%lnot.ext = zext i1 %cmp20 to i32
store i32 %lnot.ext, i32* @B, align 4
br label %for.inc
for.inc:
%tmp7 = phi i32 [ %tmp4, %for.body ], [ %lnot.ext, %if.then ]
%inc = add nuw nsw i32 %inc.iv, 1
%cmp9 = icmp ult i32 %inc, 401
br i1 %cmp9, label %for.body, label %exit
exit:
ret void
}