[llvm] r334318 - [SCEV] Look through zero-extends in howFarToZero
Krzysztof Parzyszek via llvm-commits
llvm-commits at lists.llvm.org
Fri Jun 8 13:43:07 PDT 2018
Author: kparzysz
Date: Fri Jun 8 13:43:07 2018
New Revision: 334318
URL: http://llvm.org/viewvc/llvm-project?rev=334318&view=rev
Log:
[SCEV] Look through zero-extends in howFarToZero
An expression like
(zext i2 {(trunc i32 (1 + %B) to i2),+,1}<%while.body> to i32)
will become zero exactly when the nested value becomes zero in its type.
Strip injective operations from the input value in howFarToZero to make
the value simpler.
Differential Revision: https://reviews.llvm.org/D47951
Added:
llvm/trunk/test/Analysis/ScalarEvolution/strip-injective-zext.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=334318&r1=334317&r2=334318&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/ScalarEvolution.h (original)
+++ llvm/trunk/include/llvm/Analysis/ScalarEvolution.h Fri Jun 8 13:43:07 2018
@@ -1833,6 +1833,9 @@ private:
const SCEV *getOrCreateMulExpr(SmallVectorImpl<const SCEV *> &Ops,
SCEV::NoWrapFlags Flags);
+ /// Return x if \p Val is f(x) where f is a 1-1 function.
+ const SCEV *stripInjectiveFunctions(const SCEV *Val) const;
+
/// Find all of the loops transitively used in \p S, and fill \p LoopsUsed.
/// A loop is considered "used" by an expression if it contains
/// an add rec on said loop.
Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=334318&r1=334317&r2=334318&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Fri Jun 8 13:43:07 2018
@@ -8150,6 +8150,14 @@ const SCEV *ScalarEvolution::getSCEVAtSc
return getSCEVAtScope(getSCEV(V), L);
}
+const SCEV *ScalarEvolution::stripInjectiveFunctions(const SCEV *S) const {
+ if (const SCEVZeroExtendExpr *ZExt = dyn_cast<SCEVZeroExtendExpr>(S))
+ return stripInjectiveFunctions(ZExt->getOperand());
+ if (const SCEVSignExtendExpr *SExt = dyn_cast<SCEVSignExtendExpr>(S))
+ return stripInjectiveFunctions(SExt->getOperand());
+ return S;
+}
+
/// Finds the minimum unsigned root of the following equation:
///
/// A * X = B (mod N)
@@ -8279,7 +8287,9 @@ ScalarEvolution::howFarToZero(const SCEV
return getCouldNotCompute(); // Otherwise it will loop infinitely.
}
- const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(V);
+ const SCEVAddRecExpr *AddRec =
+ dyn_cast<SCEVAddRecExpr>(stripInjectiveFunctions(V));
+
if (!AddRec && AllowPredicates)
// Try to make this an AddRec using runtime tests, in the first X
// iterations of this loop, where X is the SCEV expression found by the
Added: llvm/trunk/test/Analysis/ScalarEvolution/strip-injective-zext.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/strip-injective-zext.ll?rev=334318&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/strip-injective-zext.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/strip-injective-zext.ll Fri Jun 8 13:43:07 2018
@@ -0,0 +1,45 @@
+; RUN: opt -analyze -scalar-evolution < %s | FileCheck %s
+
+; The initial SCEV for the backedge count is
+; (zext i2 {(trunc i32 (1 + %a1) to i2),+,1}<%b2> to i32).
+; In howFarToZero, this was further converted to an add-rec, the complexity
+; of which defeated the calculation of the backedge taken count.
+; Since such zero-extensions preserve the values being extended, strip
+; them in howFarToZero to simplify the input SCEV.
+
+; Check that the backedge taken count was actually computed:
+; CHECK: Determining loop execution counts for: @f0
+; CHECK-NEXT: Loop %b2: backedge-taken count is (-1 * (trunc i32 (1 + %a1) to i2))
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64"
+
+define i32 @f0(i32 %a0, i32 %a1, i32* nocapture %a2) #0 {
+b0:
+ %v0 = and i32 %a1, 3
+ %v1 = icmp eq i32 %v0, 0
+ br i1 %v1, label %b4, label %b1
+
+b1: ; preds = %b0
+ %v2 = shl i32 %a0, 7
+ %v3 = add i32 %v2, -128
+ br label %b2
+
+b2: ; preds = %b2, %b1
+ %v4 = phi i32 [ %a1, %b1 ], [ %v9, %b2 ]
+ %v5 = phi i32* [ %a2, %b1 ], [ %v8, %b2 ]
+ %v6 = getelementptr inbounds i32, i32* %v5, i32 0
+ store i32 %v3, i32* %v6, align 4
+ %v8 = getelementptr inbounds i32, i32* %v5, i32 1
+ %v9 = add nsw i32 %v4, 1
+ %v10 = and i32 %v9, 3
+ %v11 = icmp eq i32 %v10, 0
+ br i1 %v11, label %b3, label %b2
+
+b3: ; preds = %b2
+ br label %b4
+
+b4: ; preds = %b3, %b0
+ ret i32 0
+}
+
+attributes #0 = { norecurse nounwind }
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