[PATCH] D79369: [InstCombine] "X - (X / C) * C == 0" to "X & C-1 == 0"

[Egor Bogatov via Phabricator via llvm-commits]

EgorBo updated this revision to Diff 262062.
EgorBo added a comment.

Moved to InstCombiner::visitAdd


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D79369/new/

https://reviews.llvm.org/D79369

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
  llvm/test/Transforms/InstCombine/icmp-div-constant.ll


Index: llvm/test/Transforms/InstCombine/icmp-div-constant.ll
===================================================================
--- llvm/test/Transforms/InstCombine/icmp-div-constant.ll
+++ llvm/test/Transforms/InstCombine/icmp-div-constant.ll
@@ -38,6 +38,19 @@
   ret i1 %r
 }
 
+define i1 @is_rem32_pos_decomposed_i8(i8 %x) {
+; CHECK-LABEL: @is_rem32_pos_decomposed_i8(
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[X:%.*]], -97
+; CHECK-NEXT:    [[R:%.*]] = icmp sgt i8 [[TMP1]], 0
+; CHECK-NEXT:    ret i1 [[R]]
+;
+  %d = sdiv i8 %x, 32
+  %m = mul nsw i8 %d, 32
+  %s = sub nsw i8 %x, %m
+  %r = icmp eq i8 %s, 0
+  ret i1 %r
+}
+
 ; i16 -32765 == 32771 == 0b1000000000000011
 
 define i1 @is_rem4_neg_i16(i16 %x) {
Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1306,6 +1306,19 @@
   // X % C0 + (( X / C0 ) % C1) * C0 => X % (C0 * C1)
   if (Value *V = SimplifyAddWithRemainder(I)) return replaceInstUsesWith(I, V);
 
+  // ((X / C1) << C2) + X => X % C1
+  // where C1 = 1 << C2
+  const APInt *C1, *C2;
+  if (match(LHS, m_Shl(m_SDiv(m_Value(A), m_APInt(C1)), m_APInt(C2)))) {
+    if ((RHS == A) && C1->abs().isPowerOf2() && C1->isNegative()) {
+      APInt one(C2->getBitWidth(), 1);
+      if ((C1->abs() == one.shl(*C2)) && C2->sgt(one)) {
+        Constant *NewRHS = ConstantInt::get(RHS->getType(), C1->abs());
+        return replaceInstUsesWith(I, Builder.CreateSRem(RHS, NewRHS, "srem"));
+      }
+    }
+  }
+
   // A+B --> A|B iff A and B have no bits set in common.
   if (haveNoCommonBitsSet(LHS, RHS, DL, &AC, &I, &DT))
     return BinaryOperator::CreateOr(LHS, RHS);


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