InstCombine: Optimize x/INT_MIN to x==INT_MIN

The result of x/INT_MIN is either 0 or 1, we can just use an icmp
instead.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212167 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 497c0b49ab3fcecf61be08e7cc87f9ebd0e515cc..6c6e7d8151634b37bbce43ff4ec7977a0ef67ec0 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -993,6 +993,10 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
   }
 
   if (Constant *RHS = dyn_cast<Constant>(Op1)) {
+    // X/INT_MIN -> X == INT_MIN
+    if (RHS->isMinSignedValue())
+      return new ZExtInst(Builder->CreateICmpEQ(Op0, Op1), I.getType());
+
     // -X/C  -->  X/-C  provided the negation doesn't overflow.
     if (SubOperator *Sub = dyn_cast<SubOperator>(Op0))
       if (match(Sub->getOperand(0), m_Zero()) && Sub->hasNoSignedWrap())

diff --git a/test/Transforms/InstCombine/sub.ll b/test/Transforms/InstCombine/sub.ll
index 5ff0ed5b40c1211c1bef29c728722964a853e776..67b7c4996b075fce5b29b98d012120a84bd93027 100644 (file)
--- a/test/Transforms/InstCombine/sub.ll
+++ b/test/Transforms/InstCombine/sub.ll
@@ -450,9 +450,9 @@ define <2 x i32> @test37(<2 x i32> %A) {
   %sub = sub nsw <2 x i32> zeroinitializer, %div
   ret <2 x i32> %sub
 ; CHECK-LABEL: @test37(
-; CHECK-NEXT: [[DIV:%.*]] = sdiv <2 x i32> %A, <i32 -2147483648, i32 -2147483648>
-; CHECK-NEXT: [[SUB:%.*]] = sub nsw <2 x i32> zeroinitializer, %div
-; CHECK-NEXT: ret <2 x i32> [[SUB]]
+; CHECK-NEXT: [[ICMP:%.*]] = icmp eq <2 x i32> %A, <i32 -2147483648, i32 -2147483648>
+; CHECK-NEXT: [[SEXT:%.*]] = sext <2 x i1> [[ICMP]] to <2 x i32>
+; CHECK-NEXT: ret <2 x i32> [[SEXT]]
 }
 
 define i32 @test38(i32 %A) {
@@ -460,7 +460,7 @@ define i32 @test38(i32 %A) {
   %sub = sub nsw i32 0, %div
   ret i32 %sub
 ; CHECK-LABEL: @test38(
-; CHECK-NEXT: [[DIV:%.*]] = sdiv i32 %A, -2147483648
-; CHECK-NEXT: [[SUB:%.*]] = sub nsw i32 0, [[DIV]]
-; CHECK-NEXT: ret i32 [[SUB]]
+; CHECK-NEXT: [[ICMP:%.*]] = icmp eq i32 %A, -2147483648
+; CHECK-NEXT: [[SEXT:%.*]] = sext i1 [[ICMP]] to i32
+; CHECK-NEXT: ret i32 [[SEXT]]
 }