From 4d4c54d29ff911f59fe2be1a31331dbcbb741f5f Mon Sep 17 00:00:00 2001
From: Shuxin Yang <shuxin.llvm@gmail.com>
Date: Sat, 27 Apr 2013 18:02:12 +0000
Subject: [PATCH] Fix a XOR reassociation bug.
When Reassociator optimize "(x | C1)" ^ "(X & C2)", it may swap the two
subexpressions, however, it forgot to swap cached constants (of C1 and C2)
accordingly.
rdar://13739160
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180676 91177308-0d34-0410-b5e6-96231b3b80d8
---
lib/Transforms/Scalar/Reassociate.cpp | 9 +++++---
test/Transforms/Reassociate/xor_reassoc.ll | 27 ++++++++++++++++++++++
2 files changed, 33 insertions(+), 3 deletions(-)
diff --git a/lib/Transforms/Scalar/Reassociate.cpp b/lib/Transforms/Scalar/Reassociate.cpp
index fc3b38ee53b..a3c241dc0f2 100644
--- a/lib/Transforms/Scalar/Reassociate.cpp
+++ b/lib/Transforms/Scalar/Reassociate.cpp
@@ -1195,9 +1195,6 @@ bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
if (X != Opnd2->getSymbolicPart())
return false;
- const APInt &C1 = Opnd1->getConstPart();
- const APInt &C2 = Opnd2->getConstPart();
-
// This many instruction become dead.(At least "Opnd1 ^ Opnd2" will die.)
int DeadInstNum = 1;
if (Opnd1->getValue()->hasOneUse())
@@ -1215,6 +1212,8 @@ bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
if (Opnd2->isOrExpr())
std::swap(Opnd1, Opnd2);
+ const APInt &C1 = Opnd1->getConstPart();
+ const APInt &C2 = Opnd2->getConstPart();
APInt C3((~C1) ^ C2);
// Do not increase code size!
@@ -1230,6 +1229,8 @@ bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
} else if (Opnd1->isOrExpr()) {
// Xor-Rule 3: (x | c1) ^ (x | c2) = (x & c3) ^ c3 where c3 = c1 ^ c2
//
+ const APInt &C1 = Opnd1->getConstPart();
+ const APInt &C2 = Opnd2->getConstPart();
APInt C3 = C1 ^ C2;
// Do not increase code size
@@ -1244,6 +1245,8 @@ bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
} else {
// Xor-Rule 4: (x & c1) ^ (x & c2) = (x & (c1^c2))
//
+ const APInt &C1 = Opnd1->getConstPart();
+ const APInt &C2 = Opnd2->getConstPart();
APInt C3 = C1 ^ C2;
Res = createAndInstr(I, X, C3);
}
diff --git a/test/Transforms/Reassociate/xor_reassoc.ll b/test/Transforms/Reassociate/xor_reassoc.ll
index d371a9b5b68..b9353c7f81f 100644
--- a/test/Transforms/Reassociate/xor_reassoc.ll
+++ b/test/Transforms/Reassociate/xor_reassoc.ll
@@ -164,3 +164,30 @@ define void @xor_bug1() {
%3 = and i64 undef, %2
ret void
}
+
+; The bug was that when the compiler optimize "(x | c1)" ^ "(x & c2)", it may
+; swap the two xor-subexpressions if they are not in canoninical order; however,
+; when optimizer swaps two sub-expressions, if forgot to swap the cached value
+; of c1 and c2 accordingly, hence cause the problem.
+;
+define i32 @xor_bug2(i32, i32, i32, i32) {
+ %5 = mul i32 %0, 123
+ %6 = add i32 %2, 24
+ %7 = add i32 %1, 8
+ %8 = and i32 %1, 3456789
+ %9 = or i32 %8, 4567890
+ %10 = and i32 %1, 543210987
+ %11 = or i32 %1, 891034567
+ %12 = and i32 %2, 255
+ %13 = xor i32 %9, %10
+ %14 = xor i32 %11, %13
+ %15 = xor i32 %5, %14
+ %16 = and i32 %3, 255
+ %17 = xor i32 %16, 42
+ %18 = add i32 %6, %7
+ %19 = add i32 %18, %12
+ %20 = add i32 %19, %15
+ ret i32 %20
+;CHECK: @xor_bug2
+;CHECK: xor i32 %5, 891034567
+}