[PATCH] D56679: [InstCombine] Avoid undoing 0 - (X * Y) canonicalization when combining subs.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: spatel, lebedev.ri, hfinkel, shchenz.

Otherwise instcombine gets stuck in a cycle. The canonicalization was
added in D55691 <https://reviews.llvm.org/D55691>.

This patch fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=12400


https://reviews.llvm.org/D56679

Files:
  lib/Transforms/InstCombine/InstCombineAddSub.cpp
  test/Transforms/InstCombine/mul.ll


Index: test/Transforms/InstCombine/mul.ll
===================================================================
--- test/Transforms/InstCombine/mul.ll
+++ test/Transforms/InstCombine/mul.ll
@@ -501,3 +501,17 @@
   %mul2 = mul i32 %mul, %neg
   ret i32 %mul2
 }
+
+ at X = global i32 5
+
+define i64 @test_mul_canonicalize_neg_is_not_undone(i64 %L1) {
+; CHECK-LABEL: @test_mul_canonicalize_neg_is_not_undone(
+; CHECK-NEXT:    [[TMP1:%.*]] = mul i64 [[L1:%.*]], ptrtoint (i32* @X to i64)
+; CHECK-NEXT:    [[B4:%.*]] = sub i64 0, [[TMP1]]
+; CHECK-NEXT:    ret i64 [[B4]]
+;
+  %v1 = ptrtoint i32* @X to i64
+  %B8 = sub i64 0, %v1
+  %B4 = mul i64 %B8, %L1
+  ret i64 %B4
+}
Index: lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1654,9 +1654,10 @@
       return BinaryOperator::CreateAdd(Op0, Builder.CreateMul(A, B));
 
     // X - A*CI -> X + A*-CI
+    // We have to make sure we do not undo the 0 - (X * Y) canonicalization.
     // No need to handle commuted multiply because multiply handling will
     // ensure constant will be move to the right hand side.
-    if (match(Op1, m_Mul(m_Value(A), m_Constant(CI)))) {
+    if (!match(Op0, m_ZeroInt()) && match(Op1, m_Mul(m_Value(A), m_Constant(CI)))) {
       Value *NewMul = Builder.CreateMul(A, ConstantExpr::getNeg(CI));
       return BinaryOperator::CreateAdd(Op0, NewMul);
     }


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