[PATCH] D42341: [LLVM][PASSES][InstSimplify] Add (X << Y) % X -> 0

[Anton Bikineev via Phabricator via llvm-commits]

AntonBikineev created this revision.
AntonBikineev added reviewers: spatel, lebedev.ri.

@spatel
I've added that missing fold you mentioned in https://reviews.llvm.org/D42032. I'll also quickly add new tests in a separated patch and rebase this patch as soon as those tests get committed.


Repository:
  rL LLVM

https://reviews.llvm.org/D42341

Files:
  lib/Analysis/InstructionSimplify.cpp


Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -1040,6 +1040,13 @@
        match(Op0, m_URem(m_Value(), m_Specific(Op1)))))
     return Op0;
 
+  // (X << Y) % X -> 0
+  if ((Opcode == Instruction::SRem &&
+       match(Op0, m_NSWShl(m_Specific(Op1), m_Value()))) ||
+      (Opcode == Instruction::URem &&
+       match(Op0, m_NUWShl(m_Specific(Op1), m_Value()))))
+    return Constant::getNullValue(Op0->getType());
+
   // If the operation is with the result of a select instruction, check whether
   // operating on either branch of the select always yields the same value.
   if (isa<SelectInst>(Op0) || isa<SelectInst>(Op1))


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