6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-09-26 09:18:56 +00:00
Code Issues Projects Releases Wiki Activity

InstCombine: Don't miscompile (x lshr C1) udiv C2

Browse Source 
We have a transform that changes:
  (x lshr C1) udiv C2
into:
  x udiv (C2 << C1)

However, it is unsafe to do so if C2 << C1 discards any of C2's bits.

This fixes PR21255.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219634 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2014-10-13 21:48:30 +00:00
parent 2061a56b8a
commit dfe81adbce
4 changed files with 40 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
lib/Support/APInt.cpp
View File

@@ -2064,19 +2064,29 @@ APInt APInt::umul_ov(const APInt &RHS, bool &Overflow) const {
return Res;
}
APInt APInt::sshl_ov(unsigned ShAmt, bool &Overflow) const {
Overflow = ShAmt >= getBitWidth();
APInt APInt::sshl_ov(const APInt &ShAmt, bool &Overflow) const {
Overflow = ShAmt.uge(getBitWidth());
if (Overflow)
ShAmt = getBitWidth()-1;
return APInt(BitWidth, 0);
if (isNonNegative()) // Don't allow sign change.
Overflow = ShAmt >= countLeadingZeros();
Overflow = ShAmt.uge(countLeadingZeros());
else
Overflow = ShAmt >= countLeadingOnes();
Overflow = ShAmt.uge(countLeadingOnes());
return *this << ShAmt;
}
APInt APInt::ushl_ov(const APInt &ShAmt, bool &Overflow) const {
Overflow = ShAmt.uge(getBitWidth());
if (Overflow)
return APInt(BitWidth, 0);
Overflow = ShAmt.ugt(countLeadingZeros());
return *this << ShAmt;
}