[llvm] r312329 - [SCEV] Add URem support to SCEV
Alexandre Isoard via llvm-commits
llvm-commits at lists.llvm.org
Fri Sep 1 07:59:59 PDT 2017
Author: aisoard
Date: Fri Sep 1 07:59:59 2017
New Revision: 312329
URL: http://llvm.org/viewvc/llvm-project?rev=312329&view=rev
Log:
[SCEV] Add URem support to SCEV
In LLVM IR the following code:
%r = urem <ty> %t, %b
is equivalent to
%q = udiv <ty> %t, %b
%s = mul <ty> nuw %q, %b
%r = sub <ty> nuw %t, %q ; (t / b) * b + (t % b) = t
As UDiv, Mul and Sub are already supported by SCEV, URem can be implemented
with minimal effort using that relation:
%r --> (-%b * (%t /u %b)) + %t
We implement two special cases:
- if %b is 1, the result is always 0
- if %b is a power-of-two, we produce a zext/trunc based expression instead
That is, the following code:
%r = urem i32 %t, 65536
Produces:
%r --> (zext i16 (trunc i32 %a to i16) to i32)
Note that while this helps get a tighter bound on the range analysis and the
known-bits analysis, this exposes some normalization shortcoming of SCEVs:
%div = udim i32 %a, 65536
%mul = mul i32 %div, 65536
%rem = urem i32 %a, 65536
%add = add i32 %mul, %rem
Will usually not be reduced.
Added:
llvm/trunk/test/Analysis/ScalarEvolution/flattened-0.ll
llvm/trunk/test/Analysis/ScalarEvolution/urem-0.ll
- copied, changed from r306722, llvm/trunk/test/Analysis/ScalarEvolution/urem-0.ll
Modified:
llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
llvm/trunk/lib/Analysis/ScalarEvolution.cpp
Modified: llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ScalarEvolution.h?rev=312329&r1=312328&r2=312329&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/ScalarEvolution.h (original)
+++ llvm/trunk/include/llvm/Analysis/ScalarEvolution.h Fri Sep 1 07:59:59 2017
@@ -1269,6 +1269,7 @@ public:
}
const SCEV *getUDivExpr(const SCEV *LHS, const SCEV *RHS);
const SCEV *getUDivExactExpr(const SCEV *LHS, const SCEV *RHS);
+ const SCEV *getURemExpr(const SCEV *LHS, const SCEV *RHS);
const SCEV *getAddRecExpr(const SCEV *Start, const SCEV *Step, const Loop *L,
SCEV::NoWrapFlags Flags);
const SCEV *getAddRecExpr(SmallVectorImpl<const SCEV *> &Operands,
Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=312329&r1=312328&r2=312329&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Fri Sep 1 07:59:59 2017
@@ -2981,6 +2981,34 @@ const SCEV *ScalarEvolution::getMulExpr(
return getOrCreateMulExpr(Ops, Flags);
}
+/// Represents an unsigned remainder expression based on unsigned division.
+const SCEV *ScalarEvolution::getURemExpr(const SCEV *LHS,
+ const SCEV *RHS) {
+ assert(getEffectiveSCEVType(LHS->getType()) ==
+ getEffectiveSCEVType(RHS->getType()) &&
+ "SCEVURemExpr operand types don't match!");
+
+ // Short-circuit easy cases
+ if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
+ // If constant is one, the result is trivial
+ if (RHSC->getValue()->isOne())
+ return getZero(LHS->getType()); // X urem 1 --> 0
+
+ // If constant is a power of two, fold into a zext(trunc(LHS)).
+ if (RHSC->getAPInt().isPowerOf2()) {
+ Type *FullTy = LHS->getType();
+ Type *TruncTy =
+ IntegerType::get(getContext(), RHSC->getAPInt().logBase2());
+ return getZeroExtendExpr(getTruncateExpr(LHS, TruncTy), FullTy);
+ }
+ }
+
+ // Fallback to %a == %x urem %y == %x -<nuw> ((%x udiv %y) *<nuw> %y)
+ const SCEV *UDiv = getUDivExpr(LHS, RHS);
+ const SCEV *Mult = getMulExpr(UDiv, RHS, SCEV::FlagNUW);
+ return getMinusSCEV(LHS, Mult, SCEV::FlagNUW);
+}
+
/// Get a canonical unsigned division expression, or something simpler if
/// possible.
const SCEV *ScalarEvolution::getUDivExpr(const SCEV *LHS,
@@ -4144,6 +4172,7 @@ static Optional<BinaryOp> MatchBinaryOp(
case Instruction::Sub:
case Instruction::Mul:
case Instruction::UDiv:
+ case Instruction::URem:
case Instruction::And:
case Instruction::Or:
case Instruction::AShr:
@@ -5782,6 +5811,8 @@ const SCEV *ScalarEvolution::createSCEV(
}
case Instruction::UDiv:
return getUDivExpr(getSCEV(BO->LHS), getSCEV(BO->RHS));
+ case Instruction::URem:
+ return getURemExpr(getSCEV(BO->LHS), getSCEV(BO->RHS));
case Instruction::Sub: {
SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap;
if (BO->Op)
Added: llvm/trunk/test/Analysis/ScalarEvolution/flattened-0.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/flattened-0.ll?rev=312329&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/flattened-0.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/flattened-0.ll Fri Sep 1 07:59:59 2017
@@ -0,0 +1,22 @@
+; RUN: opt < %s -scalar-evolution -analyze | FileCheck %s
+
+define void @foo([7 x i8]* %a) {
+; CHECK-LABEL: @foo
+entry:
+ br label %bb
+
+bb:
+ %idx = phi i64 [ 0, %entry ], [ %idx.incr, %bb ]
+ %i = udiv i64 %idx, 7
+ %j = urem i64 %idx, 7
+ %a.ptr = getelementptr [7 x i8], [7 x i8]* %a, i64 %i, i64 %j
+; CHECK: %a.ptr = getelementptr [7 x i8], [7 x i8]* %a, i64 %i, i64 %j
+; CHECK-NEXT: --> {%a,+,1}<nw><%bb>
+ %val = load i8, i8* %a.ptr
+ %idx.incr = add i64 %idx, 1
+ %test = icmp ne i64 %idx.incr, 35
+ br i1 %test, label %bb, label %exit
+
+exit:
+ ret void
+}
Copied: llvm/trunk/test/Analysis/ScalarEvolution/urem-0.ll (from r306722, llvm/trunk/test/Analysis/ScalarEvolution/urem-0.ll)
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/urem-0.ll?p2=llvm/trunk/test/Analysis/ScalarEvolution/urem-0.ll&p1=llvm/trunk/test/Analysis/ScalarEvolution/urem-0.ll&r1=306722&r2=312329&rev=312329&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/urem-0.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/urem-0.ll Fri Sep 1 07:59:59 2017
@@ -1,15 +1,33 @@
; RUN: opt < %s -scalar-evolution -analyze | FileCheck %s
define i8 @foo(i8 %a) {
+; CHECK-LABEL: @foo
%t0 = urem i8 %a, 27
-; CHECK: %t0
+; CHECK: %t0 = urem i8 %a, 27
; CHECK-NEXT: --> ((-27 * (%a /u 27)) + %a)
ret i8 %t0
}
define i8 @bar(i8 %a) {
+; CHECK-LABEL: @bar
%t1 = urem i8 %a, 1
-; CHECK: %t1
+; CHECK: %t1 = urem i8 %a, 1
; CHECK-NEXT: --> 0
ret i8 %t1
}
+
+define i8 @baz(i8 %a) {
+; CHECK-LABEL: @baz
+ %t2 = urem i8 %a, 32
+; CHECK: %t2 = urem i8 %a, 32
+; CHECK-NEXT: --> (zext i5 (trunc i8 %a to i5) to i8)
+ ret i8 %t2
+}
+
+define i8 @qux(i8 %a) {
+; CHECK-LABEL: @qux
+ %t3 = urem i8 %a, 2
+; CHECK: %t3 = urem i8 %a, 2
+; CHECK-NEXT: --> (zext i1 (trunc i8 %a to i1) to i8)
+ ret i8 %t3
+}
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