RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2025-02-01 05:01:59 +01:00
Code Issues Projects Releases Wiki Activity

PR13326: Fix a subtle edge case in the udiv -> magic multiply generator.

Browse Source 
This caused 6 of 65k possible 8 bit udivs to be wrong.

llvm-svn: 160058
This commit is contained in:
Benjamin Kramer 2012-07-11 18:31:59 +00:00
parent 0f2aecdfe8
commit e4bd0cdfa8
2 changed files with 22 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
lib/Support/APInt.cpp
View File

@ -1446,7 +1446,7 @@ APInt::mu APInt::magicu(unsigned LeadingZeros) const {
APInt signedMin = APInt::getSignedMinValue(d.getBitWidth());
APInt signedMax = APInt::getSignedMaxValue(d.getBitWidth());
nc = allOnes - (-d).urem(d);
nc = allOnes - (allOnes - d).urem(d);
p = d.getBitWidth() - 1; // initialize p
q1 = signedMin.udiv(nc); // initialize q1 = 2p/nc
r1 = signedMin - q1*nc; // initialize r1 = rem(2p,nc)

21
test/CodeGen/X86/divide-by-constant.ll
View File

@ -71,3 +71,24 @@ define i32 @test7(i32 %x) nounwind {
; CHECK-NOT: shrl
; CHECK: ret
}
; PR13326
define i8 @test8(i8 %x) nounwind {
%div = udiv i8 %x, 78
ret i8 %div
; CHECK: test8:
; CHECK: shrb %
; CHECK: imull $211
; CHECK: shrl $13
; CHECK: ret
}
define i8 @test9(i8 %x) nounwind {
%div = udiv i8 %x, 116
ret i8 %div
; CHECK: test9:
; CHECK: shrb $2
; CHECK: imull $71
; CHECK: shrl $11
; CHECK: ret
}