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

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160058 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp
index 6a74883803c8776b7283f67356b021c6263bd71c..38cfaed9d217a10142871f099b86fb979e6246f1 100644 (file)
--- a/lib/Support/APInt.cpp
+++ b/lib/Support/APInt.cpp
@@ -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)

diff --git a/test/CodeGen/X86/divide-by-constant.ll b/test/CodeGen/X86/divide-by-constant.ll
index e577ecb85aa83f582e3b4cae797f3d0814afa9e5..8e7c13d8efa9cdc706e8db05e5a6aed7482c1e18 100644 (file)
--- a/test/CodeGen/X86/divide-by-constant.ll
+++ b/test/CodeGen/X86/divide-by-constant.ll
@@ -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
+}