[llvm] 703423c - [InstCombine] relax constraint on udiv fold

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2023-02-20T15:08:32-05:00
New Revision: 703423c26965cd2e5b331e587d87f8ee291d956a

URL: https://github.com/llvm/llvm-project/commit/703423c26965cd2e5b331e587d87f8ee291d956a
DIFF: https://github.com/llvm/llvm-project/commit/703423c26965cd2e5b331e587d87f8ee291d956a.diff

LOG: [InstCombine] relax constraint on udiv fold

The pair of div folds was just added with:
4966d8ebe1bbe5bd6a4d28

But as noted in the post-commit review, we don't actually need
the no-remainder requirement for an unsigned division (still
need the no-unsigned-wrap though):
https://alive2.llvm.org/ce/z/qHjK3Q

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 8ca99db8f476..57e90076e187 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1027,16 +1027,20 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
 
     // Distribute div over add to eliminate a matching div/mul pair:
     // ((X * C2) + C1) / C2 --> X + C1/C2
+    // We need a multiple of the divisor for a signed add constant, but
+    // unsigned is fine with any constant pair.
     if (IsSigned &&
         match(Op0, m_NSWAdd(m_NSWMul(m_Value(X), m_SpecificInt(*C2)),
                             m_APInt(C1))) &&
-        isMultiple(*C1, *C2, Quotient, IsSigned))
+        isMultiple(*C1, *C2, Quotient, IsSigned)) {
       return BinaryOperator::CreateNSWAdd(X, ConstantInt::get(Ty, Quotient));
+    }
     if (!IsSigned &&
         match(Op0, m_NUWAdd(m_NUWMul(m_Value(X), m_SpecificInt(*C2)),
-                            m_APInt(C1))) &&
-        isMultiple(*C1, *C2, Quotient, IsSigned))
-      return BinaryOperator::CreateNUWAdd(X, ConstantInt::get(Ty, Quotient));
+                            m_APInt(C1)))) {
+      return BinaryOperator::CreateNUWAdd(X,
+                                          ConstantInt::get(Ty, C1->udiv(*C2)));
+    }
 
     if (!C2->isZero()) // avoid X udiv 0
       if (Instruction *FoldedDiv = foldBinOpIntoSelectOrPhi(I))

diff  --git a/llvm/test/Transforms/InstCombine/div.ll b/llvm/test/Transforms/InstCombine/div.ll
index 3f0b593d8581..59871f51b929 100644
--- a/llvm/test/Transforms/InstCombine/div.ll
+++ b/llvm/test/Transforms/InstCombine/div.ll
@@ -1552,13 +1552,11 @@ define i6 @sdiv_distribute_mul_nsw_add_nsw_not_multiple_offset(i6 %x) {
   ret i6 %div
 }
 
-; negative test - constants must be evenly divisible
+; constants do not have to be evenly divisible with unsigned division
 
 define i6 @udiv_distribute_mul_nuw_add_nuw_not_multiple_offset(i6 %x) {
 ; CHECK-LABEL: @udiv_distribute_mul_nuw_add_nuw_not_multiple_offset(
-; CHECK-NEXT:    [[MUL:%.*]] = mul nuw i6 [[X:%.*]], 3
-; CHECK-NEXT:    [[ADD:%.*]] = add nuw i6 [[MUL]], 7
-; CHECK-NEXT:    [[DIV:%.*]] = udiv i6 [[ADD]], 3
+; CHECK-NEXT:    [[DIV:%.*]] = add nuw i6 [[X:%.*]], 2
 ; CHECK-NEXT:    ret i6 [[DIV]]
 ;
   %mul = mul nuw i6 %x, 3