<div dir="ltr">This has regressed on our internal build, I'll send you the details off the list.</div><div class="gmail_extra"><br><div class="gmail_quote">2014-10-14 1:48 GMT+04:00 David Majnemer <span dir="ltr"><<a href="mailto:david.majnemer@gmail.com" target="_blank">david.majnemer@gmail.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: majnemer<br>
Date: Mon Oct 13 16:48:30 2014<br>
New Revision: 219634<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=219634&view=rev" target="_blank">http://llvm.org/viewvc/llvm-project?rev=219634&view=rev</a><br>
Log:<br>
InstCombine: Don't miscompile (x lshr C1) udiv C2<br>
<br>
We have a transform that changes:<br>
(x lshr C1) udiv C2<br>
into:<br>
x udiv (C2 << C1)<br>
<br>
However, it is unsafe to do so if C2 << C1 discards any of C2's bits.<br>
<br>
This fixes PR21255.<br>
<br>
Modified:<br>
llvm/trunk/include/llvm/ADT/APInt.h<br>
llvm/trunk/lib/Support/APInt.cpp<br>
llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp<br>
llvm/trunk/test/Transforms/InstCombine/div.ll<br>
<br>
Modified: llvm/trunk/include/llvm/ADT/APInt.h<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/APInt.h?rev=219634&r1=219633&r2=219634&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/APInt.h?rev=219634&r1=219633&r2=219634&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/include/llvm/ADT/APInt.h (original)<br>
+++ llvm/trunk/include/llvm/ADT/APInt.h Mon Oct 13 16:48:30 2014<br>
@@ -945,7 +945,8 @@ public:<br>
APInt sdiv_ov(const APInt &RHS, bool &Overflow) const;<br>
APInt smul_ov(const APInt &RHS, bool &Overflow) const;<br>
APInt umul_ov(const APInt &RHS, bool &Overflow) const;<br>
- APInt sshl_ov(unsigned Amt, bool &Overflow) const;<br>
+ APInt sshl_ov(const APInt &Amt, bool &Overflow) const;<br>
+ APInt ushl_ov(const APInt &Amt, bool &Overflow) const;<br>
<br>
/// \brief Array-indexing support.<br>
///<br>
<br>
Modified: llvm/trunk/lib/Support/APInt.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/APInt.cpp?rev=219634&r1=219633&r2=219634&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/APInt.cpp?rev=219634&r1=219633&r2=219634&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/lib/Support/APInt.cpp (original)<br>
+++ llvm/trunk/lib/Support/APInt.cpp Mon Oct 13 16:48:30 2014<br>
@@ -2064,19 +2064,29 @@ APInt APInt::umul_ov(const APInt &RHS, b<br>
return Res;<br>
}<br>
<br>
-APInt APInt::sshl_ov(unsigned ShAmt, bool &Overflow) const {<br>
- Overflow = ShAmt >= getBitWidth();<br>
+APInt APInt::sshl_ov(const APInt &ShAmt, bool &Overflow) const {<br>
+ Overflow = ShAmt.uge(getBitWidth());<br>
if (Overflow)<br>
- ShAmt = getBitWidth()-1;<br>
+ return APInt(BitWidth, 0);<br>
<br>
if (isNonNegative()) // Don't allow sign change.<br>
- Overflow = ShAmt >= countLeadingZeros();<br>
+ Overflow = ShAmt.uge(countLeadingZeros());<br>
else<br>
- Overflow = ShAmt >= countLeadingOnes();<br>
+ Overflow = ShAmt.uge(countLeadingOnes());<br>
<br>
return *this << ShAmt;<br>
}<br>
<br>
+APInt APInt::ushl_ov(const APInt &ShAmt, bool &Overflow) const {<br>
+ Overflow = ShAmt.uge(getBitWidth());<br>
+ if (Overflow)<br>
+ return APInt(BitWidth, 0);<br>
+<br>
+ Overflow = ShAmt.ugt(countLeadingZeros());<br>
+<br>
+ return *this << ShAmt;<br>
+}<br>
+<br>
<br>
<br>
<br>
<br>
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp?rev=219634&r1=219633&r2=219634&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp?rev=219634&r1=219633&r2=219634&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp (original)<br>
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp Mon Oct 13 16:48:30 2014<br>
@@ -965,11 +965,17 @@ Instruction *InstCombiner::visitUDiv(Bin<br>
return Common;<br>
<br>
// (x lshr C1) udiv C2 --> x udiv (C2 << C1)<br>
- if (Constant *C2 = dyn_cast<Constant>(Op1)) {<br>
+ {<br>
Value *X;<br>
- Constant *C1;<br>
- if (match(Op0, m_LShr(m_Value(X), m_Constant(C1))))<br>
- return BinaryOperator::CreateUDiv(X, ConstantExpr::getShl(C2, C1));<br>
+ const APInt *C1, *C2;<br>
+ if (match(Op0, m_LShr(m_Value(X), m_APInt(C1))) &&<br>
+ match(Op1, m_APInt(C2))) {<br>
+ bool Overflow;<br>
+ APInt C2ShlC1 = C2->ushl_ov(*C1, Overflow);<br>
+ if (!Overflow)<br>
+ return BinaryOperator::CreateUDiv(<br>
+ X, ConstantInt::get(X->getType(), C2ShlC1));<br>
+ }<br>
}<br>
<br>
// (zext A) udiv (zext B) --> zext (A udiv B)<br>
<br>
Modified: llvm/trunk/test/Transforms/InstCombine/div.ll<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/div.ll?rev=219634&r1=219633&r2=219634&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/div.ll?rev=219634&r1=219633&r2=219634&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/test/Transforms/InstCombine/div.ll (original)<br>
+++ llvm/trunk/test/Transforms/InstCombine/div.ll Mon Oct 13 16:48:30 2014<br>
@@ -132,11 +132,11 @@ define i32 @test15(i32 %a, i32 %b) nounw<br>
}<br>
<br>
define <2 x i64> @test16(<2 x i64> %x) nounwind {<br>
- %shr = lshr <2 x i64> %x, <i64 3, i64 5><br>
- %div = udiv <2 x i64> %shr, <i64 4, i64 6><br>
+ %shr = lshr <2 x i64> %x, <i64 5, i64 5><br>
+ %div = udiv <2 x i64> %shr, <i64 6, i64 6><br>
ret <2 x i64> %div<br>
; CHECK-LABEL: @test16(<br>
-; CHECK-NEXT: udiv <2 x i64> %x, <i64 32, i64 192><br>
+; CHECK-NEXT: udiv <2 x i64> %x, <i64 192, i64 192><br>
; CHECK-NEXT: ret <2 x i64><br>
}<br>
<br>
@@ -264,3 +264,13 @@ define i32 @test30(i32 %a) {<br>
; CHECK-LABEL: @test30(<br>
; CHECK-NEXT: ret i32 %a<br>
}<br>
+<br>
+define <2 x i32> @test31(<2 x i32> %x) nounwind {<br>
+ %shr = lshr <2 x i32> %x, <i32 31, i32 31><br>
+ %div = udiv <2 x i32> %shr, <i32 2147483647, i32 2147483647><br>
+ ret <2 x i32> %div<br>
+; CHECK-LABEL: @test31(<br>
+; CHECK-NEXT: %[[shr:.*]] = lshr <2 x i32> %x, <i32 31, i32 31><br>
+; CHECK-NEXT: udiv <2 x i32> %[[shr]], <i32 2147483647, i32 2147483647><br>
+; CHECK-NEXT: ret <2 x i32><br>
+}<br>
<br>
<br>
_______________________________________________<br>
llvm-commits mailing list<br>
<a href="mailto:llvm-commits@cs.uiuc.edu">llvm-commits@cs.uiuc.edu</a><br>
<a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits" target="_blank">http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits</a><br>
</blockquote></div><br></div>