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[LVI] Add select handling 

Teach LVI to handle select instructions in the exact same way it handles PHI nodes.  This is useful since various parts of the optimizer convert PHI nodes into selects and we don't want these transformations to cause inferior optimization.  

Note that this patch does nothing to exploit the implied constraint on the inputs represented by the select condition itself.  That will be a later patch and is blocked on http://reviews.llvm.org/D14476

llvm-svn: 259429
This commit is contained in:
Philip Reames 2016-02-01 22:57:53 +00:00
parent c097337493
commit c0bdb0c1e5
2 changed files with 118 additions and 0 deletions
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49
llvm/lib/Analysis/LazyValueInfo.cpp
View File

@ -389,6 +389,8 @@ namespace {
Value *Val, BasicBlock *BB);
bool solveBlockValuePHINode(LVILatticeVal &BBLV,
PHINode *PN, BasicBlock *BB);
bool solveBlockValueSelect(LVILatticeVal &BBLV,
SelectInst *S, BasicBlock *BB);
bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
Instruction *BBI, BasicBlock *BB);
void mergeAssumeBlockValueConstantRange(Value *Val, LVILatticeVal &BBLV,
@ -587,6 +589,13 @@ bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
return true;
}
if (auto *SI = dyn_cast<SelectInst>(BBI)) {
if (!solveBlockValueSelect(Res, SI, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
// If this value is a nonnull pointer, record it's range and bailout.
PointerType *PT = dyn_cast<PointerType>(BBI->getType());
if (PT && isKnownNonNull(BBI)) {
@ -809,6 +818,46 @@ void LazyValueInfoCache::mergeAssumeBlockValueConstantRange(Value *Val,
}
}
bool LazyValueInfoCache::solveBlockValueSelect(LVILatticeVal &BBLV,
SelectInst *SI, BasicBlock *BB) {
// Recurse on our inputs if needed
if (!hasBlockValue(SI->getTrueValue(), BB)) {
if (pushBlockValue(std::make_pair(BB, SI->getTrueValue())))
return false;
BBLV.markOverdefined();
return true;
}
LVILatticeVal TrueVal = getBlockValue(SI->getTrueValue(), BB);
// If we hit overdefined, don't ask more queries. We want to avoid poisoning
// extra slots in the table if we can.
if (TrueVal.isOverdefined()) {
BBLV.markOverdefined();
return true;
}
if (!hasBlockValue(SI->getFalseValue(), BB)) {
if (pushBlockValue(std::make_pair(BB, SI->getFalseValue())))
return false;
BBLV.markOverdefined();
return true;
}
LVILatticeVal FalseVal = getBlockValue(SI->getFalseValue(), BB);
// If we hit overdefined, don't ask more queries. We want to avoid poisoning
// extra slots in the table if we can.
if (FalseVal.isOverdefined()) {
BBLV.markOverdefined();
return true;
}
LVILatticeVal Result; // Start Undefined.
Result.mergeIn(TrueVal, DL);
Result.mergeIn(FalseVal, DL);
assert(!Result.isOverdefined() && "Should have exited previously");
BBLV = Result;
return true;
}
bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
Instruction *BBI,
BasicBlock *BB) {

69
llvm/test/Transforms/CorrelatedValuePropagation/select.ll
View File

@ -73,3 +73,72 @@ if.end:
ret i32 %sel
; CHECK: ret i32 1
}
define i1 @test1(i32* %p, i1 %unknown) {
; CHECK-LABEL: @test1
%pval = load i32, i32* %p
%cmp1 = icmp slt i32 %pval, 255
br i1 %cmp1, label %next, label %exit
next:
%min = select i1 %unknown, i32 %pval, i32 5
;; TODO: This pointless branch shouldn't be neccessary
br label %next2
next2:
; CHECK-LABEL: next2:
; CHECK: ret i1 false
%res = icmp eq i32 %min, 255
ret i1 %res
exit:
; CHECK-LABEL: exit:
; CHECK: ret i1 true
ret i1 true
}
; Check that we take a conservative meet
define i1 @test2(i32* %p, i32 %qval, i1 %unknown) {
; CHECK-LABEL: test2
%pval = load i32, i32* %p
%cmp1 = icmp slt i32 %pval, 255
br i1 %cmp1, label %next, label %exit
next:
%min = select i1 %unknown, i32 %pval, i32 %qval
;; TODO: This pointless branch shouldn't be neccessary
br label %next2
next2:
; CHECK-LABEL: next2
; CHECK: ret i1 %res
%res = icmp eq i32 %min, 255
ret i1 %res
exit:
; CHECK-LABEL: exit:
; CHECK: ret i1 true
ret i1 true
}
; Same as @test2, but for the opposite select input
define i1 @test3(i32* %p, i32 %qval, i1 %unknown) {
; CHECK-LABEL: test3
%pval = load i32, i32* %p
%cmp1 = icmp slt i32 %pval, 255
br i1 %cmp1, label %next, label %exit
next:
%min = select i1 %unknown, i32 %qval, i32 %pval
;; TODO: This pointless branch shouldn't be neccessary
br label %next2
next2:
; CHECK-LABEL: next2
; CHECK: ret i1 %res
%res = icmp eq i32 %min, 255
ret i1 %res
exit:
; CHECK-LABEL: exit:
; CHECK: ret i1 true
ret i1 true
}