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Lower llvm.expect intrinsic correctly for i1 

LowerExpectIntrinsic previously only understood the idiom of an expect
intrinsic followed by a comparison with zero. For llvm.expect.i1, the
comparison would be stripped by the early-cse pass.

Patch by Daniel Micay.

llvm-svn: 200664
This commit is contained in:
Duncan P. N. Exon Smith 2014-02-02 22:43:55 +00:00
parent d11c478ac3
commit 1ff08e389f
3 changed files with 51 additions and 5 deletions
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4
llvm/docs/LangRef.rst
View File

@ -8975,8 +8975,12 @@ on the ``min`` argument).
Syntax:
"""""""
This is an overloaded intrinsic. You can use ``llvm.expect`` on any
integer bit width.
::
declare i1 @llvm.expect.i1(i1 <val>, i1 <expected_val>)
declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>)
declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>)

19
llvm/lib/Transforms/Utils/LowerExpectIntrinsic.cpp
View File

@ -94,15 +94,25 @@ bool LowerExpectIntrinsic::HandleIfExpect(BranchInst *BI) {
return false;
// Handle non-optimized IR code like:
// %expval = call i64 @llvm.expect.i64.i64(i64 %conv1, i64 1)
// %expval = call i64 @llvm.expect.i64(i64 %conv1, i64 1)
// %tobool = icmp ne i64 %expval, 0
// br i1 %tobool, label %if.then, label %if.end
//
// Or the following simpler case:
// %expval = call i1 @llvm.expect.i1(i1 %cmp, i1 1)
// br i1 %expval, label %if.then, label %if.end
CallInst *CI;
ICmpInst *CmpI = dyn_cast<ICmpInst>(BI->getCondition());
if (!CmpI || CmpI->getPredicate() != CmpInst::ICMP_NE)
if (!CmpI) {
CI = dyn_cast<CallInst>(BI->getCondition());
} else {
if (CmpI->getPredicate() != CmpInst::ICMP_NE)
return false;
CI = dyn_cast<CallInst>(CmpI->getOperand(0));
}
CallInst *CI = dyn_cast<CallInst>(CmpI->getOperand(0));
if (!CI)
return false;
@ -127,7 +137,10 @@ bool LowerExpectIntrinsic::HandleIfExpect(BranchInst *BI) {
BI->setMetadata(LLVMContext::MD_prof, Node);
if (CmpI)
CmpI->setOperand(0, ArgValue);
else
BI->setCondition(ArgValue);
return true;
}

29
llvm/test/Transforms/LowerExpectIntrinsic/basic.ll
View File

@ -245,6 +245,35 @@ return: ; preds = %if.end, %if.then
declare i32 @llvm.expect.i32(i32, i32) nounwind readnone
; CHECK-LABEL: @test9(
define i32 @test9(i32 %x) nounwind uwtable ssp {
entry:
%retval = alloca i32, align 4
%x.addr = alloca i32, align 4
store i32 %x, i32* %x.addr, align 4
%tmp = load i32* %x.addr, align 4
%cmp = icmp sgt i32 %tmp, 1
%expval = call i1 @llvm.expect.i1(i1 %cmp, i1 1)
; CHECK: !prof !0
; CHECK-NOT: @llvm.expect
br i1 %expval, label %if.then, label %if.end
if.then: ; preds = %entry
%call = call i32 (...)* @f()
store i32 %call, i32* %retval
br label %return
if.end: ; preds = %entry
store i32 1, i32* %retval
br label %return
return: ; preds = %if.end, %if.then
%0 = load i32* %retval
ret i32 %0
}
declare i1 @llvm.expect.i1(i1, i1) nounwind readnone
; CHECK: !0 = metadata !{metadata !"branch_weights", i32 64, i32 4}
; CHECK: !1 = metadata !{metadata !"branch_weights", i32 4, i32 64}
; CHECK: !2 = metadata !{metadata !"branch_weights", i32 4, i32 64, i32 4}