[llvm] [InstCombine] Simplify fractions when there is no overflow (PR #92949)

[via llvm-commits]

https://github.com/AtariDreams updated https://github.com/llvm/llvm-project/pull/92949

>From b7c5a8e108bb0dc669ee8857de91a4f9908dd431 Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Tue, 21 May 2024 14:09:05 -0400
Subject: [PATCH] [InstCombine] Simplify fractions when there is no overlap

https://alive2.llvm.org/ce/z/-36zkQ
---
 .../InstCombine/InstCombineMulDivRem.cpp      | 39 +++++++++++++
 llvm/test/Transforms/InstCombine/div.ll       | 56 +++++++++++++++++++
 2 files changed, 95 insertions(+)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index ca1b1921404d8..4d554f21d77e3 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1176,6 +1176,45 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
         Mul->setHasNoSignedWrap(OBO->hasNoSignedWrap());
         return Mul;
       }
+
+      // We can reduce expressions of things like * 150 / 100 to * 3 / 2
+      if (Op0->hasOneUse() && !C2->isZero() &&
+          !(IsSigned && C1->isMinSignedValue() && C2->isAllOnes())) {
+        assert(!C2->isMinSignedValue() &&
+               "This should have been folded away by InstSimplify");
+        APInt GCD = APIntOps::GreatestCommonDivisor(C1->abs(), C2->abs());
+        if (!GCD.isOne() && !GCD.isZero()) {
+          APInt NewC1;
+          APInt NewC2;
+          if (IsSigned && C1->isNegative() && C2->isNegative()) {
+            NewC1 = C1->abs().udiv(GCD);
+            NewC2 = C2->abs().udiv(GCD);
+          } else if (IsSigned) {
+            NewC1 = C1->sdiv(GCD);
+            NewC2 = C2->sdiv(GCD);
+          } else {
+            NewC1 = C1->udiv(GCD);
+            NewC2 = C2->udiv(GCD);
+          }
+
+          auto *NewMul = Builder.CreateMul(
+              X, ConstantInt::get(Ty, NewC1), "",
+              /*NUW*/ cast<OverflowingBinaryOperator>(Op0)->hasNoUnsignedWrap(),
+              /*NSW*/ true);
+
+          if (IsSigned) {
+            auto *NewDiv =
+                BinaryOperator::CreateSDiv(NewMul, ConstantInt::get(Ty, NewC2));
+            NewDiv->setIsExact(I.isExact());
+            return NewDiv;
+          }
+
+          auto *NewDiv =
+              BinaryOperator::CreateUDiv(NewMul, ConstantInt::get(Ty, NewC2));
+          NewDiv->setIsExact(I.isExact());
+          return NewDiv;
+        }
+      }
     }
 
     if ((IsSigned && match(Op0, m_NSWShl(m_Value(X), m_APInt(C1))) &&
diff --git a/llvm/test/Transforms/InstCombine/div.ll b/llvm/test/Transforms/InstCombine/div.ll
index e8a25ff44d029..e2e03f635b1d9 100644
--- a/llvm/test/Transforms/InstCombine/div.ll
+++ b/llvm/test/Transforms/InstCombine/div.ll
@@ -1678,6 +1678,62 @@ define i32 @sdiv_sdiv_mul_nsw_exact_use(i32 %x, i32 %y, i32 %z) {
   ret i32 %r
 }
 
+define i32 @x_times_150_over_100(i32 %x) {
+; CHECK-LABEL: @x_times_150_over_100(
+; CHECK-NEXT:    [[TMP1:%.*]] = mul nuw nsw i32 [[X:%.*]], 3
+; CHECK-NEXT:    [[D1:%.*]] = lshr i32 [[TMP1]], 1
+; CHECK-NEXT:    ret i32 [[D1]]
+;
+  %m = mul nuw nsw i32 %x, 150
+  %d = udiv i32 %m, 100
+  ret i32 %d
+}
+
+define i32 @x_times_150_over_100_sdiv(i32 %x) {
+; CHECK-LABEL: @x_times_150_over_100_sdiv(
+; CHECK-NEXT:    [[TMP1:%.*]] = mul nuw nsw i32 [[X:%.*]], 3
+; CHECK-NEXT:    [[D:%.*]] = sdiv i32 [[TMP1]], 2
+; CHECK-NEXT:    ret i32 [[D]]
+;
+  %m = mul nuw nsw i32 %x, 150
+  %d = sdiv i32 %m, 100
+  ret i32 %d
+}
+
+define i32 @x_times_150_over_100_sdiv_negative(i32 %x) {
+; CHECK-LABEL: @x_times_150_over_100_sdiv_negative(
+; CHECK-NEXT:    [[TMP1:%.*]] = mul nuw nsw i32 [[X:%.*]], -3
+; CHECK-NEXT:    [[D:%.*]] = sdiv i32 [[TMP1]], 2
+; CHECK-NEXT:    ret i32 [[D]]
+;
+  %m = mul nuw nsw i32 %x, -150
+  %d = sdiv i32 %m, 100
+  ret i32 %d
+}
+
+define i32 @x_times_150_over_100_sdiv_negative_2(i32 %x) {
+; CHECK-LABEL: @x_times_150_over_100_sdiv_negative_2(
+; CHECK-NEXT:    [[TMP1:%.*]] = mul nuw nsw i32 [[X:%.*]], 3
+; CHECK-NEXT:    [[D:%.*]] = sdiv i32 [[TMP1]], -2
+; CHECK-NEXT:    ret i32 [[D]]
+;
+  %m = mul nuw nsw i32 %x, 150
+  %d = sdiv i32 %m, -100
+  ret i32 %d
+}
+
+define i32 @x_times_150_over_100_sdiv_double_negative(i32 %x) {
+; CHECK-LABEL: @x_times_150_over_100_sdiv_double_negative(
+; CHECK-NEXT:    [[TMP1:%.*]] = mul nuw nsw i32 [[X:%.*]], 3
+; CHECK-NEXT:    [[D:%.*]] = sdiv i32 [[TMP1]], 2
+; CHECK-NEXT:    ret i32 [[D]]
+;
+  %m = mul nuw nsw i32 %x, -150
+  %d = sdiv i32 %m, -100
+  ret i32 %d
+}
+
+
 ; negative test - must have nsw
 
 define i8 @sdiv_sdiv_mul_nuw(i8 %x, i8 %y, i8 %z) {