[PATCH] D41554: [InstSimplify] Missed optimization in math expression: (x+x)/x == 2

[Dmitry Venikov via Phabricator via llvm-commits]

Quolyk created this revision.
Quolyk added reviewers: eli.friedman, hfinkel, RKSimon, davide, spatel.

Motivation: https://bugs.llvm.org/show_bug.cgi?id=35709. I'm not sure how do I need to handle NSWSHL, NUWSHL, SHL


https://reviews.llvm.org/D41554

Files:
  lib/Analysis/InstructionSimplify.cpp
  test/Transforms/InstSimplify/div.ll


Index: test/Transforms/InstSimplify/div.ll
===================================================================
--- test/Transforms/InstSimplify/div.ll
+++ test/Transforms/InstSimplify/div.ll
@@ -1,3 +1,4 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -instsimplify -S | FileCheck %s
 
 ; Division-by-zero is undef. UB in any vector lane means the whole op is undef.
@@ -134,4 +135,22 @@
   ret i32 %urem
 }
 
+define i32 @sdiv_nsw_doublex_x(i32 %x) {
+; CHECK-LABEL: @sdiv_nsw_doublex_x(
+; CHECK-NEXT:    ret i32 2
+;
+  %add = shl nsw i32 %x, 1
+  %div = sdiv i32 %add, %x
+  ret i32 %div
+}
+
+define i32 @udiv_doublex_x(i32 %x) {
+; CHECK-LABEL: @udiv_doublex_x(
+; CHECK-NEXT:    ret i32 2
+;
+  %add = shl i32 %x, 1
+  %div = udiv i32 %add, %x
+  ret i32 %div
+}
+
 !0 = !{i32 0, i32 3}
Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -992,6 +992,12 @@
         return X;
   }
 
+  // (X << 1) / X -> 2
+  if ((IsSigned && match(Op0, m_NSWShl(m_Specific(Op1), m_One()))) ||
+      (!IsSigned && match(Op0, m_Shl(m_Specific(Op1), m_One())))) {
+    return ConstantInt::get(Op0->getType(), 2);
+  }
+
   // (X rem Y) / Y -> 0
   if ((IsSigned && match(Op0, m_SRem(m_Value(), m_Specific(Op1)))) ||
       (!IsSigned && match(Op0, m_URem(m_Value(), m_Specific(Op1)))))


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