[PATCH] D40649: [InstCombine] Don't crash on out of bounds shifts

[Igor Laevsky via Phabricator via llvm-commits]

igor-laevsky created this revision.

This is branched from the https://reviews.llvm.org/D40390.

We can't crash instcombine when we encounter shift by unreasonable amount. Even though it's an undefined behaviour, compiler crash is incorrect.


https://reviews.llvm.org/D40649

Files:
  lib/Analysis/ValueTracking.cpp
  test/Transforms/InstCombine/out-of-bounds-indexes.ll


Index: test/Transforms/InstCombine/out-of-bounds-indexes.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/out-of-bounds-indexes.ll
@@ -0,0 +1,13 @@
+; RUN: opt < %s -instcombine -disable-output
+; Check that we don't crash on unreasonable constant indexes
+
+define i32 @test(i32 %a, i1 %x, i1 %y) {
+entry:
+  %and1 = and i32 %a, 3
+  %B = lshr i32 %and1, -2147483648
+  %cmp = icmp eq i32 %B, 1
+  tail call void @llvm.assume(i1 %cmp)
+  ret i32 %and1
+}
+
+declare void @llvm.assume(i1)
Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -650,7 +650,8 @@
     } else if (match(Arg, m_c_ICmp(Pred, m_Shl(m_V, m_ConstantInt(C)),
                                    m_Value(A))) &&
                Pred == ICmpInst::ICMP_EQ &&
-               isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
+               isValidAssumeForContext(I, Q.CxtI, Q.DT) &&
+               C->getZExtValue() < BitWidth) {
       KnownBits RHSKnown(BitWidth);
       computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I));
       // For those bits in RHS that are known, we can propagate them to known
@@ -663,7 +664,8 @@
     } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_Shl(m_V, m_ConstantInt(C))),
                                    m_Value(A))) &&
                Pred == ICmpInst::ICMP_EQ &&
-               isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
+               isValidAssumeForContext(I, Q.CxtI, Q.DT) &&
+               C->getZExtValue() < BitWidth) {
       KnownBits RHSKnown(BitWidth);
       computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I));
       // For those bits in RHS that are known, we can propagate them inverted
@@ -677,7 +679,8 @@
                      m_c_ICmp(Pred, m_Shr(m_V, m_ConstantInt(C)),
                               m_Value(A))) &&
                Pred == ICmpInst::ICMP_EQ &&
-               isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
+               isValidAssumeForContext(I, Q.CxtI, Q.DT) &&
+               C->getZExtValue() < BitWidth) {
       KnownBits RHSKnown(BitWidth);
       computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I));
       // For those bits in RHS that are known, we can propagate them to known
@@ -688,7 +691,8 @@
     } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_Shr(m_V, m_ConstantInt(C))),
                                    m_Value(A))) &&
                Pred == ICmpInst::ICMP_EQ &&
-               isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
+               isValidAssumeForContext(I, Q.CxtI, Q.DT) &&
+               C->getZExtValue() < BitWidth) {
       KnownBits RHSKnown(BitWidth);
       computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I));
       // For those bits in RHS that are known, we can propagate them inverted


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