[llvm] [InstCombine] simplify `(X * C0) / (X * C1)` into `C0 / C1`. (PR #73204)

[via llvm-commits]

https://github.com/Z572 updated https://github.com/llvm/llvm-project/pull/73204

>From 6a4b73675ea03e85ff2ba1f46620b9f2da8a0381 Mon Sep 17 00:00:00 2001
From: Zheng Junjie <zhengjunjie at iscas.ac.cn>
Date: Thu, 23 Nov 2023 11:30:54 +0800
Subject: [PATCH] [InstCombine] Simplify `(X * C0) / (X * C1)` into `C0 / C1`.

proof: https://alive2.llvm.org/ce/z/IIEKgf
---
 .../InstCombine/InstCombineMulDivRem.cpp      | 12 +++
 llvm/test/Transforms/InstCombine/div.ll       | 93 +++++++++++++++++++
 2 files changed, 105 insertions(+)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 40156726c7038b9..0032422cd3ce7c7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1207,6 +1207,18 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
     }
   }
 
+  // (X * C0) / (X * C1) --> C0 / C1
+  Constant *C0, *C1;
+  if (match(Op0, m_c_Mul(m_Value(X), m_Constant(C0))) &&
+      match(Op1, m_c_Mul(m_Specific(X), m_Constant(C1)))) {
+    auto OB0HasNSW = cast<OverflowingBinaryOperator>(Op0)->hasNoSignedWrap();
+    auto OB0HasNUW = cast<OverflowingBinaryOperator>(Op0)->hasNoUnsignedWrap();
+    if ((IsSigned && OB0HasNSW) || (!IsSigned && OB0HasNUW)) {
+      replaceOperand(I, 0, C0);
+      replaceOperand(I, 1, C1);
+      return &I;
+    };
+  }
   return nullptr;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/div.ll b/llvm/test/Transforms/InstCombine/div.ll
index cd17d10d0e1de07..2fb4873c72f5832 100644
--- a/llvm/test/Transforms/InstCombine/div.ll
+++ b/llvm/test/Transforms/InstCombine/div.ll
@@ -1432,6 +1432,99 @@ define <2 x i8> @sdiv_sdiv_mul_nsw(<2 x i8> %x, <2 x i8> %y, <2 x i8> %z) {
   ret <2 x i8> %r
 }
 
+; (X * C0) / (X * C1) --> C0 / C1
+define i8 @sdiv_mul_nsw_mul(i8 %x) {
+; CHECK-LABEL: @sdiv_mul_nsw_mul(
+; CHECK-NEXT:    ret i8 2
+;
+  %add4 = mul i8 %x, 6
+  %add5 = mul nsw i8 %x, 12
+  %div = sdiv i8 %add5, %add4
+  ret i8 %div
+}
+
+define i8 @sdiv_mul_nsw_mul_nsw(i8 %x) {
+; CHECK-LABEL: @sdiv_mul_nsw_mul_nsw(
+; CHECK-NEXT:    ret i8 2
+;
+  %add4 = mul nsw i8 %x, 5
+  %add5 = mul nsw i8 %x, 10
+  %div = sdiv i8 %add5, %add4
+  ret i8 %div
+}
+
+define i8 @sdiv_mul_mul_nsw(i8 %x) {
+; CHECK-LABEL: @sdiv_mul_mul_nsw(
+; CHECK-NEXT:    [[ADD4:%.*]] = mul nsw i8 [[X:%.*]], 10
+; CHECK-NEXT:    [[ADD5:%.*]] = mul i8 [[X]], 20
+; CHECK-NEXT:    [[DIV:%.*]] = sdiv i8 [[ADD5]], [[ADD4]]
+; CHECK-NEXT:    ret i8 [[DIV]]
+;
+  %add4 = mul nsw i8 %x, 10
+  %add5 = mul i8 %x, 20
+  %div = sdiv i8 %add5, %add4
+  ret i8 %div
+}
+
+define i8 @sdiv_mul_mul(i8 %x) {
+; CHECK-LABEL: @sdiv_mul_mul(
+; CHECK-NEXT:    [[ADD4:%.*]] = mul i8 [[X:%.*]], 10
+; CHECK-NEXT:    [[ADD5:%.*]] = mul i8 [[X]], 20
+; CHECK-NEXT:    [[DIV:%.*]] = sdiv i8 [[ADD5]], [[ADD4]]
+; CHECK-NEXT:    ret i8 [[DIV]]
+;
+  %add4 = mul i8 %x, 10
+  %add5 = mul i8 %x, 20
+  %div = sdiv i8 %add5, %add4
+  ret i8 %div
+}
+
+define i8 @udiv_mul_mul(i8 %x) {
+; CHECK-LABEL: @udiv_mul_mul(
+; CHECK-NEXT:    [[ADD4:%.*]] = mul i8 [[X:%.*]], 10
+; CHECK-NEXT:    [[ADD5:%.*]] = mul i8 [[X]], 20
+; CHECK-NEXT:    [[DIV:%.*]] = udiv i8 [[ADD5]], [[ADD4]]
+; CHECK-NEXT:    ret i8 [[DIV]]
+;
+  %add4 = mul i8 %x, 10
+  %add5 = mul i8 %x, 20
+  %div = udiv i8 %add5, %add4
+  ret i8 %div
+}
+
+define i8 @udiv_mul_nuw_mul_nuw(i8 %x) {
+; CHECK-LABEL: @udiv_mul_nuw_mul_nuw(
+; CHECK-NEXT:    ret i8 1
+;
+  %add4 = mul nuw i8 %x, 10
+  %add5 = mul nuw i8 %x, 10
+  %div = udiv i8 %add5, %add4
+  ret i8 %div
+}
+
+define i8 @udiv_mul_mul_nuw(i8 %x) {
+; CHECK-LABEL: @udiv_mul_mul_nuw(
+; CHECK-NEXT:    [[ADD4:%.*]] = mul nuw i8 [[X:%.*]], 10
+; CHECK-NEXT:    [[ADD5:%.*]] = mul i8 [[X]], 20
+; CHECK-NEXT:    [[DIV:%.*]] = udiv i8 [[ADD5]], [[ADD4]]
+; CHECK-NEXT:    ret i8 [[DIV]]
+;
+  %add4 = mul nuw i8 %x, 10
+  %add5 = mul i8 %x, 20
+  %div = udiv i8 %add5, %add4
+  ret i8 %div
+}
+
+define i8 @udiv_mul_nuw_mul(i8 %x) {
+; CHECK-LABEL: @udiv_mul_nuw_mul(
+; CHECK-NEXT:    ret i8 2
+;
+  %add4 = mul i8 %x, 10
+  %add5 = mul nuw i8 %x, 20
+  %div = udiv i8 %add5, %add4
+  ret i8 %div
+}
+
 define i32 @sdiv_sub1(i32 %arg) {
 ; CHECK-LABEL: @sdiv_sub1(
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[ARG:%.*]], -2147483648