RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2024-10-19 11:02:59 +02:00
Code Issues Projects Releases Wiki Activity

Revert "[ValueTracking] Improve ValueTracking on left shift with nsw flag"

Browse Source 
This reverts commit r278172.  It causes PR28946.

llvm-svn: 278740
This commit is contained in:
Sanjoy Das 2016-08-15 21:01:31 +00:00
parent f5eb9d9d6a
commit 2169ec7470
2 changed files with 4 additions and 37 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
lib/Analysis/ValueTracking.cpp
View File

@ -1064,22 +1064,13 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
}
case Instruction::Shl: {
// (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
auto KZF = [BitWidth, NSW](const APInt &KnownZero, unsigned ShiftAmt) {
APInt KZResult = (KnownZero << ShiftAmt) |
auto KZF = [BitWidth](const APInt &KnownZero, unsigned ShiftAmt) {
return (KnownZero << ShiftAmt) |
APInt::getLowBitsSet(BitWidth, ShiftAmt); // Low bits known 0.
// If this shift has "nsw" keyword, then the result is either a poison
// value or has the same sign bit as the first operand.
if (NSW && KnownZero.isNegative())
KZResult.setBit(BitWidth - 1);
return KZResult;
};
auto KOF = [BitWidth, NSW](const APInt &KnownOne, unsigned ShiftAmt) {
APInt KOResult = KnownOne << ShiftAmt;
if (NSW && KnownOne.isNegative())
KOResult.setBit(BitWidth - 1);
return KOResult;
auto KOF = [BitWidth](const APInt &KnownOne, unsigned ShiftAmt) {
return KnownOne << ShiftAmt;
};
computeKnownBitsFromShiftOperator(I, KnownZero, KnownOne,

24
test/Analysis/ValueTracking/known-signbit-shift.ll
View File

@ -1,24 +0,0 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
; Result of left shifting a non-negative integer
; with nsw flag should also be non-negative
define i1 @test_shift_nonnegative(i32 %a) {
; CHECK-LABEL: @test_shift_nonnegative(
; CHECK: ret i1 true
%b = lshr i32 %a, 2
%shift = shl nsw i32 %b, 3
%cmp = icmp sge i32 %shift, 0
ret i1 %cmp
}
; Result of left shifting a negative integer with
; nsw flag should also be negative
define i1 @test_shift_negative(i32 %a, i32 %b) {
; CHECK-LABEL: @test_shift_negative(
; CHECK: ret i1 true
%c = or i32 %a, -2147483648
%d = and i32 %b, 7
%shift = shl nsw i32 %c, %d
%cmp = icmp slt i32 %shift, 0
ret i1 %cmp
}