From: Sanjay Patel <spatel@rotateright.com>
Date: Thu, 26 Jul 2018 19:22:41 +0000 (+0000)
Subject: [InstCombine] fold udiv with common factor from muls with nuw
X-Git-Tag: llvmorg-7.0.0-rc1~489
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=6d6eab66e0f76c8bb908492dcc863308b66f7771;p=platform%2Fupstream%2Fllvm.git

[InstCombine] fold udiv with common factor from muls with nuw

Unfortunately, sdiv isn't as simple because of UB due to overflow.

This fold is mentioned in PR38239:
https://bugs.llvm.org/show_bug.cgi?id=38239

llvm-svn: 338059
---

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index d6adbec..63761d42 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -973,6 +973,21 @@ Instruction *InstCombiner::visitUDiv(BinaryOperator &I) {
   if (Instruction *NarrowDiv = narrowUDivURem(I, Builder))
     return NarrowDiv;
 
+  // If the udiv operands are non-overflowing multiplies with a common operand,
+  // then eliminate the common factor:
+  // (A * B) / (A * X) --> B / X (and commuted variants)
+  // TODO: The code would be reduced if we had m_c_NUWMul pattern matching.
+  // TODO: If -reassociation handled this generally, we could remove this.
+  Value *A, *B;
+  if (match(Op0, m_NUWMul(m_Value(A), m_Value(B)))) {
+    if (match(Op1, m_NUWMul(m_Specific(A), m_Value(X))) ||
+        match(Op1, m_NUWMul(m_Value(X), m_Specific(A))))
+      return BinaryOperator::CreateUDiv(B, X);
+    if (match(Op1, m_NUWMul(m_Specific(B), m_Value(X))) ||
+        match(Op1, m_NUWMul(m_Value(X), m_Specific(B))))
+      return BinaryOperator::CreateUDiv(A, X);
+  }
+
   // (LHS udiv (select (select (...)))) -> (LHS >> (select (select (...))))
   SmallVector<UDivFoldAction, 6> UDivActions;
   if (visitUDivOperand(Op0, Op1, I, UDivActions))
diff --git a/llvm/test/Transforms/InstCombine/div.ll b/llvm/test/Transforms/InstCombine/div.ll
index a35ebed..2bfa549 100644
--- a/llvm/test/Transforms/InstCombine/div.ll
+++ b/llvm/test/Transforms/InstCombine/div.ll
@@ -688,9 +688,7 @@ define <2 x i8> @div_factor_unsigned_vec(<2 x i8> %x, <2 x i8> %y) {
 
 define i8 @udiv_common_factor(i8 %x, i8 %y, i8 %z) {
 ; CHECK-LABEL: @udiv_common_factor(
-; CHECK-NEXT:    [[A:%.*]] = mul nuw i8 [[Z:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[B:%.*]] = mul nuw i8 [[Z]], [[Y:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = udiv i8 [[A]], [[B]]
+; CHECK-NEXT:    [[C:%.*]] = udiv i8 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    ret i8 [[C]]
 ;
   %a = mul nuw i8 %z, %x
@@ -701,9 +699,7 @@ define i8 @udiv_common_factor(i8 %x, i8 %y, i8 %z) {
 
 define <2 x i8> @udiv_common_factor_commute1_vec(<2 x i8> %x, <2 x i8> %y, <2 x i8> %z) {
 ; CHECK-LABEL: @udiv_common_factor_commute1_vec(
-; CHECK-NEXT:    [[A:%.*]] = mul nuw <2 x i8> [[X:%.*]], [[Z:%.*]]
-; CHECK-NEXT:    [[B:%.*]] = mul nuw <2 x i8> [[Z]], [[Y:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = udiv <2 x i8> [[A]], [[B]]
+; CHECK-NEXT:    [[C:%.*]] = udiv <2 x i8> [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    ret <2 x i8> [[C]]
 ;
   %a = mul nuw <2 x i8> %x, %z
@@ -714,9 +710,7 @@ define <2 x i8> @udiv_common_factor_commute1_vec(<2 x i8> %x, <2 x i8> %y, <2 x
 
 define i8 @udiv_common_factor_commute2(i8 %x, i8 %y, i8 %z) {
 ; CHECK-LABEL: @udiv_common_factor_commute2(
-; CHECK-NEXT:    [[A:%.*]] = mul nuw i8 [[X:%.*]], [[Z:%.*]]
-; CHECK-NEXT:    [[B:%.*]] = mul nuw i8 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[C:%.*]] = udiv i8 [[A]], [[B]]
+; CHECK-NEXT:    [[C:%.*]] = udiv i8 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    ret i8 [[C]]
 ;
   %a = mul nuw i8 %x, %z
@@ -727,9 +721,7 @@ define i8 @udiv_common_factor_commute2(i8 %x, i8 %y, i8 %z) {
 
 define i8 @udiv_common_factor_commute3(i8 %x, i8 %y, i8 %z) {
 ; CHECK-LABEL: @udiv_common_factor_commute3(
-; CHECK-NEXT:    [[A:%.*]] = mul nuw i8 [[Z:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[B:%.*]] = mul nuw i8 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[C:%.*]] = udiv i8 [[A]], [[B]]
+; CHECK-NEXT:    [[C:%.*]] = udiv i8 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    ret i8 [[C]]
 ;
   %a = mul nuw i8 %z, %x