[PATCH] D60395: [InstCombine] canonicalize sdiv with NEG operand

[ChenZheng via Phabricator via llvm-commits]

shchenz created this revision.
shchenz added reviewers: spatel, lebedev.ri, RKSimon.
Herald added a subscriber: hiraditya.
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  int foo(int i, int j)
  {
  int res = -( i / j);
  int res2 = -i / j;
  return res + res2;
  }

`clang -O3 -Ofast a.c -c`

  0: d0 00 a3 7c neg r5,r3
  4: d6 23 63 7c divw r3,r3,r4
  8: d6 23 85 7d divw r12,r5,r4
  c: 50 60 63 7c subf r3,r3,r12
  10: b4 07 63 7c extsw r3,r3
  14: 20 00 80 4e blr

We should commonning the two `divw`.

https://rise4fun.com/Alive/9G4


https://reviews.llvm.org/D60395

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
  llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
  llvm/test/Transforms/InstCombine/sdiv-canonicalize.ll


Index: llvm/test/Transforms/InstCombine/sdiv-canonicalize.ll
===================================================================
--- llvm/test/Transforms/InstCombine/sdiv-canonicalize.ll
+++ llvm/test/Transforms/InstCombine/sdiv-canonicalize.ll
@@ -3,8 +3,8 @@
 
 define i32 @test_sdiv_canonicalize_op0(i32 %x, i32 %y) {
 ; CHECK-LABEL: @test_sdiv_canonicalize_op0(
-; CHECK-NEXT:    [[NEG:%.*]] = sub nsw i32 0, [[X:%.*]]
-; CHECK-NEXT:    [[SDIV:%.*]] = sdiv i32 [[NEG]], [[Y:%.*]]
+; CHECK-NEXT:    [[NEG:%.*]] = sdiv i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[SDIV:%.*]] = sub i32 0, [[NEG]]
 ; CHECK-NEXT:    ret i32 [[SDIV]]
 ;
   %neg = sub nsw i32 0, %x
@@ -15,8 +15,8 @@
 define i32 @test_sdiv_canonicalize_op1(i32 %x, i32 %z) {
 ; CHECK-LABEL: @test_sdiv_canonicalize_op1(
 ; CHECK-NEXT:    [[Y:%.*]] = mul i32 [[Z:%.*]], 3
-; CHECK-NEXT:    [[NEG:%.*]] = sub nsw i32 0, [[X:%.*]]
-; CHECK-NEXT:    [[SDIV:%.*]] = sdiv i32 [[Y]], [[NEG]]
+; CHECK-NEXT:    [[NEG:%.*]] = sdiv i32 [[Y]], [[X:%.*]]
+; CHECK-NEXT:    [[SDIV:%.*]] = sub i32 0, [[NEG]]
 ; CHECK-NEXT:    ret i32 [[SDIV]]
 ;
   %y = mul i32 %z, 3
@@ -38,8 +38,8 @@
 
 define <2 x i32> @test_sdiv_canonicalize_vec(<2 x i32> %x, <2 x i32> %y) {
 ; CHECK-LABEL: @test_sdiv_canonicalize_vec(
-; CHECK-NEXT:    [[NEG:%.*]] = sub nsw <2 x i32> zeroinitializer, [[X:%.*]]
-; CHECK-NEXT:    [[SDIV:%.*]] = sdiv <2 x i32> [[NEG]], [[Y:%.*]]
+; CHECK-NEXT:    [[NEG:%.*]] = sdiv <2 x i32> [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[SDIV:%.*]] = sub <2 x i32> zeroinitializer, [[NEG]]
 ; CHECK-NEXT:    ret <2 x i32> [[SDIV]]
 ;
   %neg = sub nsw <2 x i32> <i32 0, i32 0>, %x
Index: llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1021,6 +1021,14 @@
       return new SExtInst(NarrowOp, Op0->getType());
     }
   }
+  
+  // -X / Y --> -(X / Y)
+  // X / -Y --> -(X / Y)
+  Value *Y;
+  if (match(&I, m_SDiv(m_OneUse(m_NSWSub(m_Zero(), m_Value(X))), m_Value(Y))) ||
+    match(&I, m_SDiv(m_Value(X), m_OneUse(m_NSWSub(m_Zero(), m_Value(Y))))))
+    return BinaryOperator::CreateNeg(
+        Builder.CreateSDiv(X, Y, I.getName(), I.isExact()));
 
   if (Constant *RHS = dyn_cast<Constant>(Op1)) {
     // X/INT_MIN -> X == INT_MIN
Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1693,8 +1693,11 @@
 
     // 0 - (X sdiv C)  -> (X sdiv -C)  provided the negation doesn't overflow.
     if (match(Op1, m_SDiv(m_Value(X), m_Constant(C))) && match(Op0, m_Zero()) &&
-        C->isNotMinSignedValue() && !C->isOneValue())
-      return BinaryOperator::CreateSDiv(X, ConstantExpr::getNeg(C));
+        C->isNotMinSignedValue() && !C->isOneValue()) {
+      auto *BO = BinaryOperator::CreateSDiv(X, ConstantExpr::getNeg(C));
+      BO->setIsExact(cast<BinaryOperator>(Op1)->isExact());
+      return BO;
+    }
 
     // 0 - (X << Y)  -> (-X << Y)   when X is freely negatable.
     if (match(Op1, m_Shl(m_Value(X), m_Value(Y))) && match(Op0, m_Zero()))


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