<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On 14 May 2014 16:42, David Majnemer <span dir="ltr"><<a href="mailto:david.majnemer@gmail.com" target="_blank">david.majnemer@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">Hi nicholas,<br>
<br>
This gets rid of a sub instruction by moving the negation to the<br>
constant when valid.<br>
<br>
<a href="http://reviews.llvm.org/D3773" target="_blank">http://reviews.llvm.org/D3773</a><br>
<br>
Files:<br>
lib/Transforms/InstCombine/InstCombineCompares.cpp<br>
test/Transforms/InstCombine/icmp.ll<br>
<br>
Index: lib/Transforms/InstCombine/InstCombineCompares.cpp<br>
===================================================================<br>
--- lib/Transforms/InstCombine/InstCombineCompares.cpp<br>
+++ lib/Transforms/InstCombine/InstCombineCompares.cpp<br>
@@ -2971,6 +2971,15 @@<br>
BO0->hasOneUse() && BO1->hasOneUse())<br>
return new ICmpInst(Pred, D, B);<br>
<br>
+ // icmp (0-X) < cst --> -cst < x<br></blockquote><div><br></div><div>We canonicalize constants on the right. This should be "icmp -x < cst --> icmp x > -cst".</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
+ if (NoOp0WrapProblem && ICmpInst::isSigned(Pred)) {<br>
+ Value *X;<br>
+ if (match(BO0, m_Neg(m_Value(X))))<br>
+ if (ConstantInt *RHSC = dyn_cast<ConstantInt>(Op1))<br>
+ if (!RHSC->isMinValue(/*isSigned=*/true))<br>
+ return new ICmpInst(I.getPredicate(), ConstantExpr::getNeg(RHSC), X);<br></blockquote><div><br></div><div>return new ICmpInst(I.getSwappedPredicate(), X, ConstantExpr::getNeg(RHSC));</div><div><br></div><div>
LGTM</div><div><br></div><div><br></div><div>Can you do something similar for m_Not and ICmpInst::isUnsigned?</div><div><br></div><div>Nick</div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
+ }<br>
+<br>
BinaryOperator *SRem = nullptr;<br>
// icmp (srem X, Y), Y<br>
if (BO0 && BO0->getOpcode() == Instruction::SRem &&<br>
Index: test/Transforms/InstCombine/icmp.ll<br>
===================================================================<br>
--- test/Transforms/InstCombine/icmp.ll<br>
+++ test/Transforms/InstCombine/icmp.ll<br>
@@ -1356,3 +1356,12 @@<br>
%z = icmp ne i32 %x, %y<br>
ret i1 %z<br>
}<br>
+<br>
+; CHECK-LABEL: @icmp_neg_cst_slt<br>
+; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp sgt i32 %a, 10<br>
+; CHECK-NEXT: ret i1 [[CMP]]<br>
+define i1 @icmp_neg_cst_slt(i32 %a) {<br>
+ %1 = sub nsw i32 0, %a<br>
+ %2 = icmp slt i32 %1, -10<br>
+ ret i1 %2<br>
+}<br>
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