[llvm] bff1f8c - [InstCombine] complete (X << Z) / (Y << Z) --> X / Y

[Ben Shi via llvm-commits]

Author: Chenbing Zheng
Date: 2022-12-23T11:56:52+08:00
New Revision: bff1f8c79beeb8f83b37be1fb23fa44330799250

URL: https://github.com/llvm/llvm-project/commit/bff1f8c79beeb8f83b37be1fb23fa44330799250
DIFF: https://github.com/llvm/llvm-project/commit/bff1f8c79beeb8f83b37be1fb23fa44330799250.diff

LOG: [InstCombine] complete (X << Z) / (Y << Z) --> X / Y

Add one more situations for this fold.
For unsigned div, 'nsw' on both shifts + 'nuw' on the dividend.

Alive2: https://alive2.llvm.org/ce/z/sELF76

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D139997

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
    llvm/test/Transforms/InstCombine/div-shift.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 96275302e86d9..6eb7a66226865 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -888,9 +888,13 @@ static Instruction *foldIDivShl(BinaryOperator &I,
     auto *Shl0 = cast<OverflowingBinaryOperator>(Op0);
     auto *Shl1 = cast<OverflowingBinaryOperator>(Op1);
 
-    // For unsigned div, we need 'nuw' on both shifts.
+    // For unsigned div, we need 'nuw' on both shifts or
+    // 'nsw' on both shifts + 'nuw' on the dividend.
     // (X << Z) / (Y << Z) --> X / Y
-    if (!IsSigned && Shl0->hasNoUnsignedWrap() && Shl1->hasNoUnsignedWrap())
+    if (!IsSigned &&
+        ((Shl0->hasNoUnsignedWrap() && Shl1->hasNoUnsignedWrap()) ||
+         (Shl0->hasNoUnsignedWrap() && Shl0->hasNoSignedWrap() &&
+          Shl1->hasNoSignedWrap())))
       Ret = BinaryOperator::CreateUDiv(X, Y);
 
     // For signed div, we need 'nsw' on both shifts + 'nuw' on the divisor.

diff  --git a/llvm/test/Transforms/InstCombine/div-shift.ll b/llvm/test/Transforms/InstCombine/div-shift.ll
index b35d8bd3175cd..4e8f0fcaa22cb 100644
--- a/llvm/test/Transforms/InstCombine/div-shift.ll
+++ b/llvm/test/Transforms/InstCombine/div-shift.ll
@@ -951,13 +951,9 @@ define i8 @udiv_shl_shl_nsw_nuw(i8 %x, i8 %y, i8 %z) {
   ret i8 %d
 }
 
-; TODO: This could fold.
-
 define i8 @udiv_shl_shl_nuw_nsw2(i8 %x, i8 %y, i8 %z) {
 ; CHECK-LABEL: @udiv_shl_shl_nuw_nsw2(
-; CHECK-NEXT:    [[XZ:%.*]] = shl nuw nsw i8 [[X:%.*]], [[Z:%.*]]
-; CHECK-NEXT:    [[YZ:%.*]] = shl nsw i8 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = udiv i8 [[XZ]], [[YZ]]
+; CHECK-NEXT:    [[D:%.*]] = udiv i8 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    ret i8 [[D]]
 ;
   %xz = shl nuw nsw i8 %x, %z