[InstCombine] Fold (X << Z) / (X * Y) -> (1 << Z) / Y

Alive2: https://alive2.llvm.org/ce/z/CBJLeP

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 6eb7a6622686578ebce5860f677007d78f6f3d13..1a113d7f340be3275947ed2a3ea8456eda60fe2d 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1057,6 +1057,18 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
     }
   }
 
+  // (X << Z) / (X * Y) -> (1 << Z) / Y
+  // TODO: Handle sdiv.
+  if (!IsSigned && Op1->hasOneUse() &&
+      match(Op0, m_NUWShl(m_Value(X), m_Value(Z))) &&
+      match(Op1, m_c_Mul(m_Specific(X), m_Value(Y))))
+    if (cast<OverflowingBinaryOperator>(Op1)->hasNoUnsignedWrap()) {
+      Instruction *NewDiv = BinaryOperator::CreateUDiv(
+          Builder.CreateShl(ConstantInt::get(Ty, 1), Z, "", /*NUW*/ true), Y);
+      NewDiv->setIsExact(I.isExact());
+      return NewDiv;
+    }
+
   if (Instruction *R = foldIDivShl(I, Builder))
     return R;
 

diff --git a/llvm/test/Transforms/InstCombine/div-shift.ll b/llvm/test/Transforms/InstCombine/div-shift.ll
index 4e8f0fcaa22cbfa33092db43cddd6c9e53e75502..b87ace5a630ef11ccdc9701d1b024dd019c8ed4b 100644 (file)
--- a/llvm/test/Transforms/InstCombine/div-shift.ll
+++ b/llvm/test/Transforms/InstCombine/div-shift.ll
@@ -528,13 +528,12 @@ define i8 @udiv_mul_shl_nsw_use3(i8 %x, i8 %y, i8 %z) {
   ret i8 %d
 }
 
-; TODO: This can fold to (1<<z) / y
+; (X << Z) / (X * Y) -> (1 << Z) / Y
 
 define i5 @udiv_shl_mul_nuw(i5 %x, i5 %y, i5 %z) {
 ; CHECK-LABEL: @udiv_shl_mul_nuw(
-; CHECK-NEXT:    [[M1:%.*]] = shl nuw i5 [[X:%.*]], [[Z:%.*]]
-; CHECK-NEXT:    [[M2:%.*]] = mul nuw i5 [[X]], [[Y:%.*]]
-; CHECK-NEXT:    [[D:%.*]] = udiv i5 [[M1]], [[M2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shl nuw i5 1, [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = udiv i5 [[TMP1]], [[Y:%.*]]
 ; CHECK-NEXT:    ret i5 [[D]]
 ;
   %m1 = shl nuw i5 %x, %z
@@ -545,9 +544,8 @@ define i5 @udiv_shl_mul_nuw(i5 %x, i5 %y, i5 %z) {
 
 define i5 @udiv_shl_mul_nuw_swap(i5 %x, i5 %y, i5 %z) {
 ; CHECK-LABEL: @udiv_shl_mul_nuw_swap(
-; CHECK-NEXT:    [[M1:%.*]] = shl nuw i5 [[X:%.*]], [[Z:%.*]]
-; CHECK-NEXT:    [[M2:%.*]] = mul nuw i5 [[Y:%.*]], [[X]]
-; CHECK-NEXT:    [[D:%.*]] = udiv i5 [[M1]], [[M2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shl nuw i5 1, [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = udiv i5 [[TMP1]], [[Y:%.*]]
 ; CHECK-NEXT:    ret i5 [[D]]
 ;
   %m1 = shl nuw i5 %x, %z
@@ -558,9 +556,8 @@ define i5 @udiv_shl_mul_nuw_swap(i5 %x, i5 %y, i5 %z) {
 
 define i5 @udiv_shl_mul_nuw_exact(i5 %x, i5 %y, i5 %z) {
 ; CHECK-LABEL: @udiv_shl_mul_nuw_exact(
-; CHECK-NEXT:    [[M1:%.*]] = shl nuw i5 [[X:%.*]], [[Z:%.*]]
-; CHECK-NEXT:    [[M2:%.*]] = mul nuw i5 [[X]], [[Y:%.*]]
-; CHECK-NEXT:    [[D:%.*]] = udiv exact i5 [[M1]], [[M2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shl nuw i5 1, [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = udiv exact i5 [[TMP1]], [[Y:%.*]]
 ; CHECK-NEXT:    ret i5 [[D]]
 ;
   %m1 = shl nuw i5 %x, %z
@@ -571,9 +568,8 @@ define i5 @udiv_shl_mul_nuw_exact(i5 %x, i5 %y, i5 %z) {
 
 define <2 x i4> @udiv_shl_mul_nuw_vec(<2 x i4> %x, <2 x i4> %y, <2 x i4> %z) {
 ; CHECK-LABEL: @udiv_shl_mul_nuw_vec(
-; CHECK-NEXT:    [[M1:%.*]] = shl nuw <2 x i4> [[X:%.*]], [[Z:%.*]]
-; CHECK-NEXT:    [[M2:%.*]] = mul nuw <2 x i4> [[Y:%.*]], [[X]]
-; CHECK-NEXT:    [[D:%.*]] = udiv <2 x i4> [[M1]], [[M2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shl nuw <2 x i4> <i4 1, i4 1>, [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = udiv <2 x i4> [[TMP1]], [[Y:%.*]]
 ; CHECK-NEXT:    ret <2 x i4> [[D]]
 ;
   %m1 = shl nuw <2 x i4> %x, %z
@@ -582,8 +578,38 @@ define <2 x i4> @udiv_shl_mul_nuw_vec(<2 x i4> %x, <2 x i4> %y, <2 x i4> %z) {
   ret <2 x i4> %d
 }
 
+define i8 @udiv_shl_mul_nuw_extra_use_of_shl(i8 %x, i8 %y, i8 %z) {
+; CHECK-LABEL: @udiv_shl_mul_nuw_extra_use_of_shl(
+; CHECK-NEXT:    [[M1:%.*]] = shl nuw i8 [[X:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    call void @use(i8 [[M1]])
+; CHECK-NEXT:    [[TMP1:%.*]] = shl nuw i8 1, [[Z]]
+; CHECK-NEXT:    [[D:%.*]] = udiv i8 [[TMP1]], [[Y:%.*]]
+; CHECK-NEXT:    ret i8 [[D]]
+;
+  %m1 = shl nuw i8 %x, %z
+  call void @use(i8 %m1)
+  %m2 = mul nuw i8 %y, %x
+  %d = udiv i8 %m1, %m2
+  ret i8 %d
+}
+
 ; negative test - extra use
 
+define i8 @udiv_shl_mul_nuw_extra_use_of_mul(i8 %x, i8 %y, i8 %z) {
+; CHECK-LABEL: @udiv_shl_mul_nuw_extra_use_of_mul(
+; CHECK-NEXT:    [[M1:%.*]] = shl nuw i8 [[X:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[M2:%.*]] = mul nuw i8 [[Y:%.*]], [[X]]
+; CHECK-NEXT:    call void @use(i8 [[M2]])
+; CHECK-NEXT:    [[D:%.*]] = udiv i8 [[M1]], [[M2]]
+; CHECK-NEXT:    ret i8 [[D]]
+;
+  %m1 = shl nuw i8 %x, %z
+  %m2 = mul nuw i8 %y, %x
+  call void @use(i8 %m2)
+  %d = udiv i8 %m1, %m2
+  ret i8 %d
+}
+
 define i8 @udiv_shl_mul_nuw_extra_use(i8 %x, i8 %y, i8 %z) {
 ; CHECK-LABEL: @udiv_shl_mul_nuw_extra_use(
 ; CHECK-NEXT:    [[M1:%.*]] = shl nuw i8 [[X:%.*]], [[Z:%.*]]