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LVI: Recognize the form instcombine canonicalizes range checks into when forming constant ranges.

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This could probably be made a lot smarter, but this is a common case and doesn't require LVI to scan a lot
of code. With this change CVP can optimize away the "shift == 0" case in Hashing.h that only gets hit when
"shift" is in a range not containing 0.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151919 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2012-03-02 15:34:43 +00:00
parent 0c7374d87e
commit 8979e5f372
2 changed files with 59 additions and 4 deletions
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20
lib/Analysis/LazyValueInfo.cpp
View File

@ -24,6 +24,7 @@
#include "llvm/Support/CFG.h"
#include "llvm/Support/ConstantRange.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/PatternMatch.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/ADT/DenseSet.h"
@ -31,6 +32,7 @@
#include <map>
#include <stack>
using namespace llvm;
using namespace PatternMatch;
char LazyValueInfo::ID = 0;
INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info",
@ -795,9 +797,8 @@ bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
// If the condition of the branch is an equality comparison, we may be
// able to infer the value.
ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
if (ICI && ICI->getOperand(0) == Val &&
isa<Constant>(ICI->getOperand(1))) {
if (ICI->isEquality()) {
if (ICI && isa<Constant>(ICI->getOperand(1))) {
if (ICI->isEquality() && ICI->getOperand(0) == Val) {
// We know that V has the RHS constant if this is a true SETEQ or
// false SETNE.
if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
@ -807,12 +808,23 @@ bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
return true;
}
if (ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1))) {
// Recognize the range checking idiom that InstCombine produces.
// (X-C1) u< C2 --> [C1, C1+C2)
ConstantInt *NegOffset = 0;
if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
match(ICI->getOperand(0), m_Add(m_Specific(Val),
m_ConstantInt(NegOffset)));
ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
// Calculate the range of values that would satisfy the comparison.
ConstantRange CmpRange(CI->getValue(), CI->getValue()+1);
ConstantRange TrueValues =
ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);
if (NegOffset) // Apply the offset from above.
TrueValues = TrueValues.subtract(NegOffset->getValue());
// If we're interested in the false dest, invert the condition.
if (!isTrueDest) TrueValues = TrueValues.inverse();

43
test/Transforms/CorrelatedValuePropagation/range.ll Normal file
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@ -0,0 +1,43 @@
; RUN: opt -correlated-propagation -S < %s | FileCheck %s
declare i32 @foo()
define i32 @test1(i32 %a) nounwind {
%a.off = add i32 %a, -8
%cmp = icmp ult i32 %a.off, 8
br i1 %cmp, label %then, label %else
then:
%dead = icmp eq i32 %a, 7
br i1 %dead, label %end, label %else
else:
ret i32 1
end:
ret i32 2
; CHECK: @test1
; CHECK: then:
; CHECK-NEXT: br i1 false, label %end, label %else
}
define i32 @test2(i32 %a) nounwind {
%a.off = add i32 %a, -8
%cmp = icmp ult i32 %a.off, 8
br i1 %cmp, label %then, label %else
then:
%dead = icmp ugt i32 %a, 15
br i1 %dead, label %end, label %else
else:
ret i32 1
end:
ret i32 2
; CHECK: @test2
; CHECK: then:
; CHECK-NEXT: br i1 false, label %end, label %else
}