[PatternMatch][InstCombine] match a vector with constant expression element(s) as a constant expression

[spatel]

Summary

The InstCombine test is reduced from issue #56601. Without the more liberal match for ConstantExpr, we try to rearrange constants in Negator forever.

Alternatively, we could adjust the definition of m_ImmConstant to be more conservative, but that's probably a larger patch, and I don't see any downside to changing m_ConstantExpr. We never capture and modify a ConstantExpr; transforms just want to avoid it.

[nikic]

LGTM. You can also drop an explicit contrainsConstantExpression() call in InstCombineCalls.

[spatel]

In D130286#3669603, @nikic wrote:

LGTM. You can also drop an explicit contrainsConstantExpression() call in InstCombineCalls.

Thanks - will update with that change.

[spatel]

Updated:
Drop an explicit call to containsConstantExpression() since the matcher covers it now.

llvm/include/llvm/IR/PatternMatch.h

inline class_match<ConstantInt> m_ConstantInt() {
   return class_match<ConstantInt>();
 }
 
 /// Match an arbitrary ConstantFP and ignore it.
 inline class_match<ConstantFP> m_ConstantFP() {
   return class_match<ConstantFP>();
 }
 
-/// Match an arbitrary ConstantExpr and ignore it.
-inline class_match<ConstantExpr> m_ConstantExpr() {
-  return class_match<ConstantExpr>();
+struct constantexpr_match {
+  template <typename ITy> bool match(ITy *V) {
+    auto *C = dyn_cast<Constant>(V);
+    return C && (isa<ConstantExpr>(C) || C->containsConstantExpression());
   }
+};
+
+/// Match a constant expression or a constant that contains a constant
+/// expression.
+inline constantexpr_match m_ConstantExpr() { return constantexpr_match(); }
 
 /// Match an arbitrary basic block value and ignore it.
 inline class_match<BasicBlock> m_BasicBlock() {
   return class_match<BasicBlock>();
 }
 
 /// Inverting matcher
 template <typename Ty> struct match_unless {

 /// Match a basic block value, capturing it if we match.
 inline bind_ty<BasicBlock> m_BasicBlock(BasicBlock *&V) { return V; }
 inline bind_ty<const BasicBlock> m_BasicBlock(const BasicBlock *&V) {
   return V;
 }
 
 /// Match an arbitrary immediate Constant and ignore it.
 inline match_combine_and<class_match<Constant>,
-                         match_unless<class_match<ConstantExpr>>>
+                         match_unless<constantexpr_match>>
 m_ImmConstant() {
   return m_CombineAnd(m_Constant(), m_Unless(m_ConstantExpr()));
 }
 
 /// Match an immediate Constant, capturing the value if we match.
 inline match_combine_and<bind_ty<Constant>,
-                         match_unless<class_match<ConstantExpr>>>
+                         match_unless<constantexpr_match>>
 m_ImmConstant(Constant *&C) {
   return m_CombineAnd(m_Constant(C), m_Unless(m_ConstantExpr()));
 }
 
 /// Match a specified Value*.
 struct specificval_ty {
   const Value *Val;
 

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

case Intrinsic::ctpop:
     break;
 
   case Intrinsic::fshl:
   case Intrinsic::fshr: {
     Value *Op0 = II->getArgOperand(0), *Op1 = II->getArgOperand(1);
     Type *Ty = II->getType();
     unsigned BitWidth = Ty->getScalarSizeInBits();
     Constant *ShAmtC;
-    if (match(II->getArgOperand(2), m_ImmConstant(ShAmtC)) &&
-        !ShAmtC->containsConstantExpression()) {
+    if (match(II->getArgOperand(2), m_ImmConstant(ShAmtC))) {
       // Canonicalize a shift amount constant operand to modulo the bit-width.
       Constant *WidthC = ConstantInt::get(Ty, BitWidth);
       Constant *ModuloC =
           ConstantFoldBinaryOpOperands(Instruction::URem, ShAmtC, WidthC, DL);
       if (!ModuloC)
         return nullptr;
       if (ModuloC != ShAmtC)
         return replaceOperand(*II, 2, ModuloC);

llvm/test/Transforms/InstCombine/sub-of-negatible.ll

if.end:
   %e.0 = phi i32 [ undef, %entry ], [ %div, %if.end ]
   %conv = trunc i32 %e.0 to i16
   %mul.i = mul nsw i16 -1, %conv
   %conv1 = sext i16 %mul.i to i32
   %div = sub nsw i32 0, %conv1
   br label %if.end
 }
 
+; This would infinite loop because we failed to match a
+; vector constant with constant expression elements as
+; a constant expression.
+
+@g = external hidden global [1 x [1 x double]]
+
+define <1 x i64> @PR56601(<1 x i64> %x, <1 x i64> %y) {
+; CHECK-LABEL: @PR56601(
+; CHECK-NEXT:    [[M1:%.*]] = mul nsw <1 x i64> [[X:%.*]], <i64 42>
+; CHECK-NEXT:    [[M2:%.*]] = mul nsw <1 x i64> [[Y:%.*]], <i64 12>
+; CHECK-NEXT:    [[A1:%.*]] = add <1 x i64> [[M1]], <i64 add (i64 ptrtoint (ptr @g to i64), i64 -4)>
+; CHECK-NEXT:    [[A2:%.*]] = add <1 x i64> [[M2]], <i64 add (i64 ptrtoint (ptr @g to i64), i64 -3)>
+; CHECK-NEXT:    [[R:%.*]] = sub <1 x i64> [[A1]], [[A2]]
+; CHECK-NEXT:    ret <1 x i64> [[R]]
+;
+  %m1 = mul nsw <1 x i64> %x, <i64 42>
+  %m2 = mul nsw <1 x i64> %y, <i64 12>
+  %a1 = add <1 x i64> %m1, <i64 add (i64 ptrtoint (ptr @g to i64), i64 -4)>
+  %a2 = add <1 x i64> %m2, <i64 add (i64 ptrtoint (ptr @g to i64), i64 -3)>
+  %r = sub <1 x i64> %a1, %a2
+  ret <1 x i64> %r
+}
+
 ; CHECK: !0 = !{!"branch_weights", i32 40, i32 1}
 !0 = !{!"branch_weights", i32 40, i32 1}

llvm/unittests/IR/PatternMatch.cpp

 TEST_F(PatternMatchTest, ConstExpr) {
   Constant *G =
       M->getOrInsertGlobal("dummy", PointerType::getUnqual(IRB.getInt32Ty()));
   Constant *S = ConstantExpr::getPtrToInt(G, IRB.getInt32Ty());
   Type *VecTy = FixedVectorType::get(IRB.getInt32Ty(), 2);
   PoisonValue *P = PoisonValue::get(VecTy);
   Constant *V = ConstantExpr::getInsertElement(P, S, IRB.getInt32(0));
 
+  // The match succeeds on a constant that is a constant expression itself
+  // or a constant that contains a constant expression.
   EXPECT_TRUE(match(S, m_ConstantExpr()));
-  EXPECT_FALSE(match(V, m_ConstantExpr()));
+  EXPECT_TRUE(match(V, m_ConstantExpr()));
 }
 
 } // anonymous namespace.