[InstCombine] improve efficiency of isFreeToInvert

This is NFC-intended when viewed from outside the pass.
I was trying to make sure that we don't infinite loop
in subtract combines and noticed that we handle the
non-canonical forms of add/sub here, but it should
not be necessary. Coding it this way seems slightly
clearer than mixing all 4 patterns as before.

diff --git a/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h b/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h
index 3f13df7..f763612 100644 (file)
--- a/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h
+++ b/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h
@@ -246,12 +246,13 @@ public:
 
     // If `V` is of the form `A + Constant` then `-1 - V` can be folded into
     // `(-1 - Constant) - A` if we are willing to invert all of the uses.
-    if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V))
-      if (BO->getOpcode() == Instruction::Add ||
-          BO->getOpcode() == Instruction::Sub)
-        if (match(BO, PatternMatch::m_c_BinOp(PatternMatch::m_Value(),
-                                              PatternMatch::m_ImmConstant())))
-          return WillInvertAllUses;
+    if (match(V, m_Add(PatternMatch::m_Value(), PatternMatch::m_ImmConstant())))
+      return WillInvertAllUses;
+
+    // If `V` is of the form `Constant - A` then `-1 - V` can be folded into
+    // `A + (-1 - Constant)` if we are willing to invert all of the uses.
+    if (match(V, m_Sub(PatternMatch::m_ImmConstant(), PatternMatch::m_Value())))
+      return WillInvertAllUses;
 
     // Selects with invertible operands are freely invertible
     if (match(V,