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Teach ComputeNumSignBits about signed divisions.

Browse Source 
http://reviews.llvm.org/D8028
rdar://20023136



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231140 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nadav Rotem 2015-03-03 21:39:02 +00:00
parent fdba200203
commit 10faa1b211
2 changed files with 40 additions and 0 deletions
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17
lib/Analysis/ValueTracking.cpp
View File

@ -1723,6 +1723,23 @@ unsigned ComputeNumSignBits(Value *V, const DataLayout *TD,
Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits();
return ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q) + Tmp;
case Instruction::SDiv:
const APInt *Denominator;
// sdiv X, C -> adds log(C) sign bits.
if (match(U->getOperand(1), m_APInt(Denominator))) {
// Ignore non-positive denominator.
if (!Denominator->isStrictlyPositive())
break;
// Calculate the incoming numerator bits.
unsigned NumBits = ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q);
// Add floor(log(C)) bits to the numerator bits.
return std::min(TyBits, NumBits + Denominator->logBase2());
}
break;
case Instruction::AShr: {
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q);
// ashr X, C -> adds C sign bits. Vectors too.

23
test/Transforms/InstCombine/intrinsics.ll
View File

@ -363,3 +363,26 @@ define i32 @cttz_select(i32 %Value) nounwind {
; CHECK-NEXT: call i32 @llvm.cttz.i32(i32 %Value, i1 false)
; CHECK-NEXT: ret i32
}
; CHECK-LABEL: @overflow_div_add(
; CHECK: ret i1 false
define i1 @overflow_div_add(i32 %v1, i32 %v2) nounwind {
entry:
%div = sdiv i32 %v1, 2
%t = call %ov.result.32 @llvm.sadd.with.overflow.i32(i32 %div, i32 1)
%obit = extractvalue %ov.result.32 %t, 1
ret i1 %obit
}
; CHECK-LABEL: @overflow_div_sub(
; CHECK: ret i1 false
define i1 @overflow_div_sub(i32 %v1, i32 %v2) nounwind {
entry:
; Check cases where the known sign bits are larger than the word size.
%a = ashr i32 %v1, 18
%div = sdiv i32 %a, 65536
%t = call %ov.result.32 @llvm.ssub.with.overflow.i32(i32 %div, i32 1)
%obit = extractvalue %ov.result.32 %t, 1
ret i1 %obit
}