[llvm-commits] [llvm] r160058 - in /llvm/trunk: lib/Support/APInt.cpp test/CodeGen/X86/divide-by-constant.ll

[Benjamin Kramer]

Author: d0k
Date: Wed Jul 11 13:31:59 2012
New Revision: 160058

URL: http://llvm.org/viewvc/llvm-project?rev=160058&view=rev
Log:
PR13326: Fix a subtle edge case in the udiv -> magic multiply generator.

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

Modified:
    llvm/trunk/lib/Support/APInt.cpp
    llvm/trunk/test/CodeGen/X86/divide-by-constant.ll

Modified: llvm/trunk/lib/Support/APInt.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/APInt.cpp?rev=160058&r1=160057&r2=160058&view=diff
==============================================================================
--- llvm/trunk/lib/Support/APInt.cpp (original)
+++ llvm/trunk/lib/Support/APInt.cpp Wed Jul 11 13:31:59 2012
@@ -1446,7 +1446,7 @@
   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)

Modified: llvm/trunk/test/CodeGen/X86/divide-by-constant.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/divide-by-constant.ll?rev=160058&r1=160057&r2=160058&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/divide-by-constant.ll (original)
+++ llvm/trunk/test/CodeGen/X86/divide-by-constant.ll Wed Jul 11 13:31:59 2012
@@ -71,3 +71,24 @@
 ; 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
+}