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InstCombine: Optimize x/INT_MIN to x==INT_MIN

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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
This commit is contained in:
David Majnemer
2014-07-02 06:42:13 +00:00
parent 5f8c844dc8
commit 3e01ae9f8f
2 changed files with 10 additions and 6 deletions
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4
lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@@ -993,6 +993,10 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
} }
if (Constant *RHS = dyn_cast<Constant>(Op1)) { 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. // -X/C --> X/-C provided the negation doesn't overflow.
if (SubOperator *Sub = dyn_cast<SubOperator>(Op0)) if (SubOperator *Sub = dyn_cast<SubOperator>(Op0))
if (match(Sub->getOperand(0), m_Zero()) && Sub->hasNoSignedWrap()) if (match(Sub->getOperand(0), m_Zero()) && Sub->hasNoSignedWrap())

12
test/Transforms/InstCombine/sub.ll
View File

@@ -450,9 +450,9 @@ define <2 x i32> @test37(<2 x i32> %A) {
%sub = sub nsw <2 x i32> zeroinitializer, %div %sub = sub nsw <2 x i32> zeroinitializer, %div
ret <2 x i32> %sub ret <2 x i32> %sub
; CHECK-LABEL: @test37( ; CHECK-LABEL: @test37(
; CHECK-NEXT: [[DIV:%.*]] = sdiv <2 x i32> %A, <i32 -2147483648, i32 -2147483648> ; CHECK-NEXT: [[ICMP:%.*]] = icmp eq <2 x i32> %A, <i32 -2147483648, i32 -2147483648>
; CHECK-NEXT: [[SUB:%.*]] = sub nsw <2 x i32> zeroinitializer, %div ; CHECK-NEXT: [[SEXT:%.*]] = sext <2 x i1> [[ICMP]] to <2 x i32>
; CHECK-NEXT: ret <2 x i32> [[SUB]] ; CHECK-NEXT: ret <2 x i32> [[SEXT]]
} }
define i32 @test38(i32 %A) { define i32 @test38(i32 %A) {
@@ -460,7 +460,7 @@ define i32 @test38(i32 %A) {
%sub = sub nsw i32 0, %div %sub = sub nsw i32 0, %div
ret i32 %sub ret i32 %sub
; CHECK-LABEL: @test38( ; CHECK-LABEL: @test38(
; CHECK-NEXT: [[DIV:%.*]] = sdiv i32 %A, -2147483648 ; CHECK-NEXT: [[ICMP:%.*]] = icmp eq i32 %A, -2147483648
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i32 0, [[DIV]] ; CHECK-NEXT: [[SEXT:%.*]] = sext i1 [[ICMP]] to i32
; CHECK-NEXT: ret i32 [[SUB]] ; CHECK-NEXT: ret i32 [[SEXT]]
} }